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Personality correlates of cannabis dependence
Vol. 4. pp, 361 to 371 Pcrgarnon Press Lid 1979. Printed in Great Britain
0306-460379, I 101-0361$02.00/0
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PERSONALITY CORRELATES OF CANNABIS DEPENDENCE* JOHN BACHMAN a n d REESE T . JONES Langley Porter Neuropsychiatric Institute University of California~ San Francisco
Abstract--The personality characteristics of 48 male volunteers were measured with the M M P I and were related to measures of cannabis withdrawal symptoms. Personality variables accounted for 25~; of the variance in these symptoms. Neurotic introversion, a tendency not to deny anxiety, absence of sensation seeking and openness were traits found to relate positively to the intensity of cannabis abstinence symptoms.
In addition to pharmacological and environmental determinants of psychoactive drug effects, individual differences in personality characteristics influence reactions to a variety of psychoactive drugs (Von Felsinger et al., 1955; Kornetsky & Humphries, 1957; Shagass, 1957; Klerman et al., 1959; Claridge & Herrington, 1960; Lindemann & Von Felsinger, 1961; Rodnight & Gooch, 1963; Nash & Stone, 1974; Claridge, 1976; Revelle et al., 1976; and Capone et al., 1976). None of these studies, however, evaluated the effect of personality on reactivity to cannabis (i.e. marijuana, hashish, THC, etc.). Several reports describe correlations between personality and levels of cannabis usage. However, the cannabis literature contains few studies of how personality differences affect the subjective experience associated with cannabis intoxication (Naditch, 1974), and very few studies which report cannabis abstinence symptoms (Jones et al., 1976). The correlational studies relating personality and cannabis usage were conducted during the last decade with students, drug treatment patients, and people in prisons and labor unions (McAree et al., 1969; Hogan et al., 1970; Zinberg & Weil, 1970; Brill et al., 1971; Harmantz et al., 1972; Knecht et al., 1972). Conceptual and methodological inadequacies limit the generalizability and validity of the findings but the results are consistent and support the hypothesis that different patterns of cannabis use are associated with different profiles on personality tests. Frequent users score higher on test scales indicative of psychopathy (i.e. impulsive, antisocial non-conformity), extraversion, sensation seeking and psychopathology. Infrequent and non-users are less antisocial and alienated but more introverted, controlled, neurotic and concerned with social achievement. These data suggest a corollary hypothesis: the personality characteristics associated with frequent cannabis use predict greater levels of cannabis withdrawal symptomatology and dependence in these people. Evidence for dependence on cannabis requires that a clear-cut and consistent withdrawal syndrome follow a period of its regular use. The syndrome may include signs and symptoms of abstinence alone and may or may not include drug-seeking behavior. Physical and psychological withdrawal symptoms occurring after abrupt cessation of prolonged cannabis intoxication have been reported in laboratory animals (Deneau & Kaymakcalan, 1971; Kaymakcalan et al., 1977) and human subjects (Williams et al., 1946; Jones et al., 1976; Nowlan & Cohen, 1977). In our laboratory (Jones et al., 1976), THC was administered orally every 4 hr in doses that were increased to 30 mg and given for 11-12 days. Tolerance developed to many of the drug's initial effects. When the THC was replaced by placebo pills under double-blind conditions, virtually every subject experienced mood changes, disturbed sleep, decreased appetite, restlessness, irritability, perspiration, chills, feverish feelings, nausea, abdominal distress, tremulousness, weight loss, loose bowel movements, hemoconcentration, sleep EEG eye movement *Research supported by funds from Contract No. HSM-42-73-181 and Grant No. DA01696 from the National Institute on Drug Abuse and Research Scientist Award No. DA00053 to Reese T. Jones, M.D., from the National Institute on Drug Abuse. 361
362
JOHN BACHMAN and REESE T. JONES
rebound, waking EEG changes and increased intraocular pressure. This withdrawal syndrome persisted for 72-96hr with most of the changes returning to pre-drug levels after 5 days. The signs and symptoms were eliminated by administration of smoked or oral doses of cannabis. Cannabis dependence was defined by the appearance of this characteristic withdrawal syndrome. This paper reports an attempt to describe the relationship between personality and variation in responses following the abrupt cessation of prolonged cannabis administration. Personality characteristics of subjects were measured by the Minnesota Multiphasic Personality Inventory (MMPI) and by Eysenck's indicators of extraversion and neuroticism. Subjects' self-reports and nurses' observations of their behavior were used to measure abstinence symptoms. METHOD
Subjects Male subjects with prior cannabis experience were recruited by advertisements in newspapers. Each subject gave his informed consent to participate in this experiment which was approved by the Committee on Human Research of the University of California, San Francisco. Subjects were paid S25.00 for each day of their participation. After thorough screening, 64 healthy and cooperative men were hospitalized and tested for 21-42 day periods. Ages ranged from 20 to 31 yr with a mean of 25 yr. Upon admission into the experiment, their mean body weight was 68.6 kg with a range of from 53.6 to 88.2 kg. Subjects had attended school for an average of 14 yr with a range of from 11 to 18 yr. They reported using marijuana regularly for an average of 5 years with a range of from 1 to 15 yr. During the 3 months prior to their participation in the experiment, they reported using marijuana "nearly every day". These men drank beer or wine on the average of "once or twice a week" and drank whiskey or hard liquor on the average of "about once a month". Many of the subjects used nicotine and caffeine daily. Men with more than infrequent and sporadic hallucinogen, stimulant, barbiturate or opiate use were not included in the experiment. One hundred thirty-three applicants completed Minnesota Multiphasic Personality Inventories (MMPIs) as part of the evaluation used to screen potential subjects. Of these 133 applicants, 64 eventually participated in the experiment. Sixty-nine applicants were excluded from participation on a variety of grounds such as physical illness, excessive polydrug use or leaving San Francisco (i.e. they were not excluded just on the basis of aberrant MMPI profiles). The mean MMPI profiles of (1) all 64 subjects, (2) a subset of 48 subjects included in some of the following analyses, and (3) the 69 excluded applicants are presented in Table 1 and Fig. 1. Forty of 64 subjects completed both M E A N M M P I PROFILES FOR ALL SUBJECTS USED IN THE EXPERIMENT (N : 64) A N D EXCLUDED APPLICANTS (N : 69)
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Personality correlates of cannabis dependence
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JOHN BACHMAN and REESE T. JONES Table 2. Mean EPI scale scores for a subset of the subjects in this experiment (N = 40)
Extraversion Neuroticism Lie Scale
M
a
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a*
27.6 13.0 3.6
6,6 6.6 3.0
28.2 21.5 3.6
6.9 8.4 2.4
* Eysenck & Eysenck (1968) sample means and standard deviations for a group of 236 American college students.
forms of the Eysenck Personality Inventory (EPI; see Eysenck & Eysenck, 1968). The mean (combined) EPI "extraversion" and "neuroticism" scale scores are presented in Table 2. Interpretation of the mean M M P I profiles of these 133 men suggests that as a group they demonstrated (1) aesthetic sensitivity and passivity (i.e. the high Mf--masculine/ feminine--scores); (2) an excessive need for stimulation and excitement (i.e. the elevated M a - - h y p o m a n i a - - s c o r e s ) ; (3) alienated and non-conformist sociopathic tendencies (i.e. the elevated Pd--psychopathic deviant--scores); and (4) an ability to cope and adapt successfully (i.e. the elevated Es---ego strength--scores). The scores on the Eysenck Personality Inventory indicate these subjects were not unlike the group of normative American college students, except they possessed considerably lower neuroticism scores.
Setting The subjects lived 24 hr per day for the entire 21-42 day duration of the experiment on a 24 bed general psychiatric unit. The unit was staffed so as to both treat psychotic patients and conduct a variety of clinical research studies. Usually, 4 research subjects lived on the ward at any given time. Subjects were permitted to leave the ward or receive visitors only when supervised by research or nursing staff. Periodic blood and urine analyses were performed to screen for non-experimental drugs. There was no restriction placed on cigarette or coffee use. Subjects participated in an extensive set of biochemical and electrophysiologic tests and performed several behavioral and cognitive tasks daily, primarily between 7:00a.m. and 5:00p.m. At other times, they were free to sleep, read, play their musical instruments, etc. Of the 48 subjects from whom withdrawal symptom data were collected and analyzed, 8 were hospitalized for 21 days, 34 stayed for 30 days and 6 spent between 35 and 42 days in the hospital.
Experimental treatments During the hospitalization, subjects received single, opaque gelatin capsules that contained from zero to 30 mg of delta-9-tetrahydrocannabinol (THC) every 4 hr. The T H C was administered in the form of either pure T H C dissolved in a sesame oil vehicle or a crude cannabis extract of 29~o THC, 2.8~o cannabidiol and 1.5% cannabinol dissolved in 0.2~).4 c m - 3 of 95~o ethanol vehicle. No differences in the effects produced by these 2 preparations were observed. The doses administered to subjects were determined on the basis of the T H C content only, which was equated between the 2 preparations. These drugs were provided by the National Institute on Drug Abuse and were assayed periodically throughout the study to determine their T H C content. The capsules were given orally under double-blind conditions by a nurse. All subjects were evaluated initially during a 3-7 day baseline, pre-drug period of placebo (i.e. vehicle) administration. After an initial 10--30mg dose of THC, the dose level was increased rapidly (i.e. over 2-3 days for 24 subjects) or slowly (i.e. over 4-6 days for the remaining 24 subjects) to the maximum amount of 30 mg every 4 hr. Thirtyfive subjects received an additional 10-30mg dose at bedtime or at noon. Thus, the total daily dose administered was between 180 and 210 mg of T H C which amounted to an average of 3.1 mg/kg per day. A rough, but commonly accepted estimate of the equivalence between oral vs smoked T H C states that smoked doses are 3 times as
Personality correlates of cannabis dependence
365
"potent" as oral doses. Thus, in Mendelson et al.'s (1974) study of marijuana selfadministration, the "heavy" users smoked an average of 6 cigarettes per day. Each contained approximately 1 g of marijuana and between 18-23 mg of THC. These subjects therefore smoked about 20 mg x 6 cigarettes, or 120 mg of THC daily. But, given that about one-half of the THC present in a cigarette is lost to the smoker in side-stream smoke and between puffs, Mendelson et al.'s subjects more realistically consumed about 60mg of THC per day. This dose compares with the 180-210mg of THC consumed daily by subjects in our experiment when the smoked dose (60mg) is multiplied by 3 to convert from smoked to oral potency. The major difference between the 2 studies is the schedule of dosage administration. In our study, the THC was administered in 30mg doses given orally every 4hr around the clock. Forty-five of the 48 subjects were maintained on the fixed maximum dose for at least 8 days. Following the period of THC administration, subjects were given placebo capsules again for between 3 and 9 days and then discharged. Cessation effects
In order to study the cannabis withdrawal syndrome, the signs and symptoms following the abrupt cessation of THC administration were measured and analyzed. Cessation effects are defined operationally in two ways: (1) as the difference between the mean values of subjective and behavioral ratings made during the first 3 days immediately following cessation of THC administration and (i.e. minus) the last 3 days of maximum dose THC administration; and (2) as the difference between the mean values of subjective and behavioral ratings made during the first 3 post-THC days and (i.e. minus) the last 3 days of the pre-THC baseline. These two definitions of the cessation effect are referred to as CEF 1 and CEF 2, respectively, in what follows. The first definition emphasizes changes in a subject's state that are associated with THC withdrawal and may only reflect the disappearance of drug effects. The second definition of cessation effects, CEF 2, is included to determine if the subjective and behavioral changes associated with the end of a period of prolonged THC intoxication represent simply the disappearance of drug effects and/or the emergence of abstinence and dependence. If the drug effects were wearing off, subjects' reports of intoxication would be expected to return to basal level and no additional subjective phenomena would be expected to occur. If abstinence were evident during the post-THC period, subjects would be expected to report symptoms different from those of intoxication and at values different than the basal level. CEF 1 represents the difference in subjects' states just before and just after withdrawal of THC while CEF 2 reflects the difference in subjects' conditions before and after the entire period of THC administration. Dependent variables
Among the many measures used to evaluate the effects of THC, one set obtained daily for each subject consisted of self-reports and nurses' reports. These were recorded on the Symptom Check List (SCL-90), the Profile of Mood States (POMS) and the Nurses' Observation Scale for Inpatient Evaluation (NOSIE) (Guy, 1976). These instruments were used in this experiment because of their demonstrated sensitivity to other psychoactive drugs and because they permitted quantification and between-subject comparison. A set of SCL-90, POMS and NOSIE scales that reflect the changes following cessation of THC administration were selected on the basis of the results of repeated measures analyses of variance that showed the temporal changes before, during and after drug administration to be statistically significant. Those scales whose mean scores changed significantly from the baseline or maximum dose administration stages to the post-drug stage were considered to reflect CEF 1 and CEF 2. The scales selected to reflect the cessation effect included "hostility" and "sleep disturbance" from the SCL-90, "anger-hostility" from the POMS and "irritability" from the NOSIE. A listing of scores on the selected scales from (1) the final 3 pre-THC days, (2) the last 3 maximum dose days and (3) the first 3 post-THC placebo days was prepared
366
JOHN BACHMAN and REESE T. JONES MEAN
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Fig. 2. Mean daily composite z scores for the CEF scales. Abscissa represents days of placebo and drug administration. "BL" refers to the last 3 baseline days. "I" refers to the initial 3 days of drug administration. "M" and "ML" refer to the consecutive days of maximum dose administration, including the last 3 days. "P" refers to the first 3 post-drug or placebo administration days.
for each subject. On the basis of this listing, each of the selected scales' scores for each of the 48 subjects on each of the listed days was standardized and combined to yield daily composite z scores for each subject. Mean daily composite z scores were c o m p u t e d by summing all of the subjects' composite z scores on a particular day and dividing the sum by the number of subjects. The mean daily composite z scores for the C E F scales are presented graphically in Fig. 2.
Personality data To reduce the number of personality variables under consideration, 17 M M P I (K-corrected) scale scores contributed by the 133 applicants to the experiment were factor analyzed (see Table 1 for the scale scores). A principal components analysis was performed and those factors with eigenvalues greater than one were rotated via the varimax procedure to obtain an orthogonal solution. Four factors were so formed. Individual factor scores for each of the 48 subjects were computed. Median factor scores for each factor were computed and subjects scoring above or below each median score were identified. RESULTS
Results of the M M P I factor analysis Given the almost parallel and nearly identical profiles between the men accepted into the study and those excluded (see Fig. 1), we decided to combine data oblaincd from all subjects and use the total sample for the factor analysis. Four factors with eigenvalues greater than one were rotated to simple, orthogonal structure. Together. they accounted for 68~o of the total variance. The rotated factor loadings of each scalc on each factor are presented in Table 3. Factor 1 accounted for 30~o of the total variance. Welch's A or "anxiety" scale, Navran's Dy or "dependency" scale, Barron's Es or "ego strength" scale (which loaded negatively), the Si scale, the F scale, the K scale (which loaded negatively), the Sc scale and the Pt scale all loaded at 0.50 or more on factor 1. This factor is quite similar in composition to others found by factor analysis of M M P I scales and has been referred to as dimension of ego-weakness vs ego-strength by Kasselb a u m et al., (1959). They interpreted the factor as one reflecting " . . . m a l a d j u s t m e n t , general neuroticism, anxiety, d e p e n d e n c y . . , as opposed to healthy non-anxious personality, absence of disorders and a tendency towards leadership and intellectual ability" (p. 233).
Personality correlates of cannabis dependence
367
Factor 2 accounted for 18~ of the total variance and, like factor 1, also reflected distress or psychopathology (indicated by the high loadings of Sc and Pt), but of a kind characterized by the denial of anxiety (high K loadings) and the tendency to express distress and conflict via somatic symptoms (high Hs and Hy loadings) or behavior disorders (high Pd loading). Factor 3 accounted for 12~o of the total variance and consisted primarily of Mac Andrew's Mc or "addiction prone" scale, the Ma scale and the D scale (which loaded negatively). This factor reflects a dimension of sensation seeking where individuals scoring +Mc, + M a and - D are characterized by their high energy level, restlessness, enthusiasm, impatience, hyperactivity, cheerfulness, spontaneity and lack of depression.. They tend to seek out and use psychoactive drugs in their pursuit of excitement. Indi-. viduals scoring - M c , - M a and + D on this factor demonstrate a low energy level, non-competitiveness, a lack of self-confidence, depression, worry and pessimism. They usually abstain from excessive psychoactive drug use. Factor 4 accounted for 8~o of the total variance. The Mf scale loaded positively and the L scale loaded negatively on factor 4. Educated, culturally oriented, interpersonally sensitive males who tend to be socially responsive, passive and able to admit minor faults easily tend to have high scores on this factor. The meaning of these four MMPI factors may be elaborated further by noting their relationship with Eysenck's dimension of extraversion/introversion, neuroticism/stability and the EPI lie validity scale. Correlation coefficients between the MMPI factors and the EPI scales are presented in Table 4. Factor 1 correlated negatively with extraversion (r (38) = -0.428, 19 < 0.01) and positively with neuroticism (r (38) = 0.529, /9 < 0.01) which confirms its identity as a factor reflecting neurotic introversion. Factor 2 correlated negatively with neuroticism (r (38) = -0.338, /9 < 0.05) which suggests that subjects scoring high on factor 2 tend to deny anxiety. Factor 3 correlated positively with extraversion (r (38) = 0.565, P < 0.01) which reflects the social ebullience and impulsivity of high factor 3 subjects. And factor 4 correlated positively with neuroticism (r (38) = 0.345, P < 0.05) which suggests the presence of anxiety in high factor 4 subjects. None of the factors correlated significantly with Eysenck's lie scale which suggests the subjects responded truthfully to the MMPI items.
Personality factors and the cessation effect CEF 1 was determined by computing the difference between the mean composite z score of the first 3 post-THC days and the mean z score of the last 3 maximum Table 3. Factor loadings of 17 M M P 1 scales on four M M P I factors derived from a principal components factor analysis with varimax rotation (N = 133) Scale loadings
Scale loadings
Scale loadings
on
on
on
on
factor 1
factor 2
factor 3
factor 4
A Dy Es Si F K Sc Pt D Pa Hy L Ma Pd Mc Mf Hs
0.89 0.85 -0.77 0.74 0.70 -0.68 0.60 0.57 0.47 0.32 -0.25 -0.17 0.13 0.11 0.08 0.06 0.00
Hs Hy Sc Pt K Pd Pa D L Ma Es Mc Si F Dy Mf A
0.83 0.80 0.61 0.60 0.56 0.54 0.43 0.38 0.30 0.23 -0.19 -0.14 -0.14 0.13 - 0.09 0.08 -0.04
Mc Ma D Si Pd Hy F Mf Pa L Sc K A Hs Es Pt Dy
0.79 0.77 -0.55 -0.44 0.31 -0.22 0.19 -0.14 0.14 - 0.11 0.11 -0.09 0.08 -0.07 - 0.07 0.02 0.01
Scale loadings
Mf L Pa Dy F Pt Hs A Mc Ma K Es Si D Sc Pd Hy
0.78 -0.51 0.36 0.36 -0.31 0.26 -0.24 0.24 -0.22 0.20 -0.19 0.14 -0.09 0.07 - 0.04 0.04 0.03
368
JOHN BACHMANand REESET. JONES Table 4. Simplecorrelations between the four MMPI factors and the three Eysenck personality scales (N = 40) Extraversion Factor Factor Factor Factor
1 2 3 4
Neuroticism
-0.428* 0.172 0.565* 0.123
Lie
0.529* -0.338t -0.108 0.345t
-0.116 -0.148 -0.185 -0.207
* P < 0.01, 38 d.f.
t P < 0.05, 38 d.f.
dose days. C E F 2 was d e t e r m i n e d by c o m p u t i n g the difference b e t w e e n the m e a n z score of the first 3 p o s t - T H C days a n d the m e a n z score of the last 3 p r e - T H C baseline days. T h e influence of the p e r s o n a l i t y factors o n the subjects' responses to the T H C w i t h d r a w a l was e x a m i n e d (1) b y a m u l t i p l e regression analysis a n d (2) by p l o t t i n g the m e a n c o m p o s i t e z scores for the 3-day periods for C E F 1 a n d C E F 2 for subjects scoring a b o v e or b e l o w the four m e d i a n M M P I factor scores (see T a b l e 5 a n d Fig. 3). T a b l e 5 presents a step-by-step s u m m a r y of the d e v e l o p m e n t of the multiple correl a t i o n s b e t w e e n C E F 1 a n d C E F 2 a n d the four p e r s o n a l i t y factors w h e n these latter variables were e n t e r e d first i n t o the regression e q u a t i o n s . T h e y were e n t e r e d into the e q u a t i o n s in such a n order that each o n e a d d e d a c c o u n t e d for m a x i m u m variance. Together, four p e r s o n a l i t y factors a c c o u n t e d for 25~o of the total variance in b o t h C E F 1 a n d C E F 2. This r e p r e s e n t e d a significant p r o p o r t i o n of the variance (i.e. R z = 0.248, F [4,43] = 3 . 5 4 5 , P < 0 . 0 5 for C E F 1 a n d R 2 = 0 . 2 5 0 , F [4,43] = 3 . 5 9 6 , P < 0 . 0 5 for C E F 2). At the fourth e n t r y step (see T a b l e 5), the partial c o r r e l a t i o n s between C E F 1 a n d factors 3 a n d 1 were significant (i.e. B for factor 3 = - 0 . 2 9 3 a n d B for factor 1 = 0.297; P < 0.05 for both). Also, at the fourth e n t r y step, the partial c o r r e l a t i o n s b e t w e e n C E F 2 a n d factors 4 a n d 3 were significant (i.e. B for factor 4 = 0.332 a n d B for factor 3 = - 0 . 2 8 7 ; P < 0.05 for both). T h e partial c o r r e l a t i o n s b e t w e e n factor 2 a n d C E F 1 a n d C E F 2 were negative b u t n o t significant (P > 0.10) Table 5. Summary of the step-by-step development of the multiple correlation between CEF 1, CEF 2 and the four MMPI personality factors Dependent Variable CEF 1
Step
Factor
1 2
3 3 1 3 1 2 3 1 2 4 4 4 3 4 3 1 4 3 1 2
3 4
CEF 2
1 2 3 4
Multiple R
R2
AR2
F test of R2 F= df=
0.305 0.417
0 . 0 9 3 0.093 4.744t 0 . 1 7 4 0.081 4.752t
1,46 2,45
0.465
0 . 2 1 7 0.043 4.068t
3,44
0.498
0 . 2 4 8 0.031
3.545t
4,43
0.323 0.431
0.104 0.104 0 . 1 8 6 0.082
5.374t 5.161t
1,46 2,45
0.473
0 . 2 2 4 0.038 4.234t
3,44
0.500
0 . 2 5 0 0.026
4,43
3.596t
F test of each B at each step B* F= d.f. = -0.305 -0.290 0.284 -0.306 0.275 - 0.207 - 0.293 0.297 -0.212 0.177 0.323 0.304 -0.286 0.328 - 0.274 0.195 0.332 -0.287 0.188 -0.163
4.744+ 4.557+ 4.409# 5.223t 4.248# 2.404 4.862t 4.951¢ 2.551 1.767 5.375+ 5.108+ 4.535+ 6.000+ 4.243+ 2.122 6.224+ 4.662t 1.998 1.529
refers to Beta, the standardized partial regression coefficient calculated on the final step. t P < 0.05 * B
1,46 1,45 1,45 1,44 1.44 1,44 1,43 1,43 1,43 1,43 1,46 1,45 1,45 1,44 1,44 1,44 1,43 1,43 1,43 1,43
Personality correlates of cannabis dependence
369
M E A N DALLY COMPOSITE Z SCORES FOR THREE DAY PERIODS USED T O C O M P U T E THE TWO CESSATION a
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Fig. 3. Mean composite z scores for 3 day periods used to compute the 2 cessation effect scores. "BL'" refers to the last 3 baseline days and "ML'" refers to the last 3 days subjects received the maximum dose of THC. "P" refers to the 3 days immediately post or following THC administration.
These statistical relationships between the personality factors and the cessation effect are represented graphically in Fig. 3. For each of the factors, there was no difference between the high and low groups' mean composite z scores before T H C withdrawal (i.e. at the points labeled "BL" or baseline and " M L " or last maximum dose days in the figure). The regression analyses showed that the partial correlations between CEF 1 and factors 1 and 3 and between CEF 2 and factors 3 and 4 were significant. Figure 3 shows that subjects with low scores on factor 3 and high scores on factors 1 and 4 reported greater symptom intensities following cessation of T H C administration. F r o m Fig. 3 it can be seen also that subjects with low factor 2 scores tended to report greater changes during the post-drug period. DISCUSSION Subjects reporte d experiencing increased feelings of tension, anger and restlessness along with exhibiting insomnia and anorexia when placebo capsules replaced the active T H C pills. Nurses' observations of increased behavioral activity and irritability corroborated the subjective reports. These changes, which occurred after the abrupt termination of a prolonged period of intoxication during which tolerance developed, may have reflected the disappearance of drug effects and/or the emergence of abstinence phenomena. Two measures of the cessation effect were included in the analyses to distinguish these possibilities. The results clearly show that both measures are greater than zero (see Fig. 3). That is, the level of symptomatic and behavioral changes during the 3 days immediately following T H C withdrawal is greater than both the baseline and last 3 maximum dose days' values. Had the post-drug level of changes been greater than the value of the final 3 drug days but equal to the pre-drug baseline value, it would have been necessary to conclude only that the drug effects were wearing off following its withdrawal. The "overshoot" of the basal values suggests the emergence of abstinence phenomena and thus, by definition, the presence of cannabis dependence. An interesting finding involves the relationship between cannabis dependence and personality. The mean M M P I profile of the experienced cannabis users who applied to and participated in this experiment was characterized by elevated scores on the Mf, Pd and Ma scales. These results are consistent with findings reported previously in the literature (Brill et al., 1971; McGuire & Megargee, 1974; Khavari et al., 1976). However, instead of using just these 3 scales (and hence ignoring the remainder of the M M P I data) and instead of using all of the scales, the entire set of scales was submitted to a factor analysis to produce orthogonal (i.e. uncorrelated) personality factor scores. The factor analysis resulted in the separation of the 3 scales associated with
370
JOHN BACHMANand REESET. JONES
marijuana use. They loaded on factors 4, 2 and 3, respectively, not on a single factor as the mean profile would suggest. This separation suggests that reliance on M M P I scale scores and profiles to infer personality characteristics may tend to distort rather than clarify patterns of personality traits by attributing to every individual a single, c o m m o n pattern. The first M M P I factor that reflected anxiety and general maladjustment and which correlated positively with Eysenck's measures of introversion and neuroticism was positively related to the magnitude of the cessation effect. This suggests that neurotic, introverted individuals who tend to complain about their lives and surroundings not surprisingly are likely to complain more intensely about the changes associated with T H C abstinence. The second personality factor that reflected a tendency to deny anxiety and which correlated negatively with Eysenck's measure of neuroticism was negatively related to the intensity of the symptoms associated with cannabis abstinence. This suggests that strong withdrawal symptoms are reported by men who tend n o t to deny anxiety while reporting increased mood and symptom changes. The third M M P I factor that reflected sensation seeking and which correlated positively with Eysenck's measure of extraversion was negatively related to the magnitude of the cessation effect. This implies that individuals who tend to seek arousal and excitement may tend to experience minimal or diminished sensations associated with T H C abstinence, especially when these are negative in feeling-tone (e.g. increased tension, anger and irritabilty). The hypothesis that the personality characteristics associated with frequent cannabis use predict greater withdrawal symptomatology is partially disconfirmed by this finding that sensation-seeking is negatively correlated with the cessation effect. The positive relationship between the cessation effect and the fourth personality factor which reflected sensitivity and openness and which correlated positively with neuroticism suggests that empathic and honest, although neurotic, men are likely to report the symptoms of cannabis abstinence more intensely. The relationships between the measures of personality and the T H C cessation effect may reflect general response tendencies or behavioral sets that determined these peoples' style of reporting subjective estimates of personality traits and mood states. While the independent behavioral observations made by the nurses were consistent with the selfreports and confirmed the occurrence of change following withdrawal of THC, the predictive value of these personality correlates of cannabis dependence are, at present, merely suggestive. The presence of neurotic introversion, a tendency not to deny anxiety, openness and the absence of sensation seeking in conjunction with regular and frequent cannabis use may predict a greater propensity for individuals with these traits to experience more intense withdrawal symptoms during cannabis abstinence. Whether or not these clusters of personality characteristics are predictive of other aspects of cannabis dependence (e.g. compulsive drug-seeking behavior) is a question for further study.
REFERENCES Brill, N., Crumpton, E. & Grayson H. Personality factors in marijuana use. Archires oj General Psychiatry, 1971, 2,t, 163-165. Burke, E. & Eichberg, R. Personality characteristics of adolescent users of dangerous drugs as indicated by the Minnesota Multiphasic Personality Inventory. The Journal of Nervous and. Mental Disease, 1972, 154, 291 298. Capone, T., Brahen, L. & Weichert, V. Personality factors and drug effects in a controlled study of cyclazocine. Journal of Clinical Psychology, 1976, 32, 489 495. Claridge, G. Individual differences in drug response. Journal of Psychosomatic Research, 1976, 20, 351-362. Claridge. G. & Herrington, R. Sedation threshold, personality, and the theory of neurosis. Journal of Mental Science, 1960, 106, 1568 1583. Deneau, G. & Kaymakcalan, S. Physiological and psychological dependence to A9-tetrahydrocannabinol (THC) in rhesus monkeys. Pharmacologist, 1971, 13, 246. Eysenck, H. & Eysenck, S. Manual for the Eysenck Personality Inventory. San Diego, CA: Educational and Industrial Testing Service, 1968. Guy, W. ECDEU Assessment Manual Jot Psychopharmacololqy.~ Rockville, Maryland, U.S. Dept. ~f Health, Education, and Welfare, publication No. (ADM)76-338, 1976.
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Harmantz, J., Shader, R. & Salzman, C. Marijuana users and non-users: Personality test differences, Archives of General Psychiatry, 1972, 26, 108-112. Hogan, R., Mankin, D., Conway, J. & Fox, S. Personality correlates of undergraduate marijuana use. Journal of Consultin 9 and Clinical Psychology, 1970, 35, 58 63. Jones, R., Benowitz, N. & Bachman, J. Clinical studies of cannabis tolerance and dependence. Annals. of the New York Academy of Sciences, 1976, 282, 221-239. Kaymakcalan, S., Ayhan, I. & Tulunay, F. Naloxone-induced or postwithdrawal abstinence signs in A9-tetrahydrocannabinol tolerant rats. Psychopharmacolooy, 1977, 55, 243-249. Kasselbaum, G., Couch, A. & Slater P. The factorial dimensions of the MMPI. Journal of Abnormal Psychology, 1959, 23, 226-236. Khavari, K., Mabry, E. & Humes, M. Personality correlates of hallucinogen use. Journal of Abnormal Psychology, 1977, 86, 172 178. Klerman, G., DiMascio, A., Rinkel, M. & Greenblatt, M. The influence of specific personality patterns on the reactions to phrenotropic agents. J. Masserman (Ed.). Biological Psychiatry. New York: Grune, 1959. Knecht, S., Cundick, B., Edwards, D. & Gunderson, E. The prediction of marijuana use from personality scales. Educational and Psychological Measurement, 1972, 32, 1111-1117. Kornetsky, C. & Humphries, Q. Relationship between effects of a number of centrally acting drugs and personality. A.M.A. Archives of Neurology and Psychiatry, 1957, 77, 325-327. Lindeman, E. & Von Felsinger, J. Drug effects and personality theory. Psychopharmacologia, 1961, 2, 69-92. McAree, C., Steffenhagen, R. & Sheutlin, L. Personality factors and patterns of drug usage in college students. American Journal of Psychiatry, 1972, 128, 890-893. McGuire, J. & Megargee, E. Personality correlates of marijuana use among youthful offenders. Journal of Consulting and Clinical Psychology, 1974, 42, 124~133. Mendelson, J., Rossi, A. M. & Meyers, R. The Use of Marijuana: A Psycholooical and Physiological Inquiry. J. Mendelson, A. M. Rossi and R. Meyer (Eds). New York: Plenum Press, 1974. Naditch, M. P. Acute adverse reactions to psychoactive drugs, drug usage and psychopathology. Journal of Abnormal Psychology, 1974, 83, 394-403. Nash, H. & Stone, G. Psychological effects of drugs: A factor analytic approach. The Journal of Nervous and Mental Disease, 1974, 159, 4 ~ 8 . Nowlan, R. & Cohen, S. Tolerance to marijuana: heart rate and subjective "high"~ Clinical Pharmacolooy and Therapeutics, 1977, 22, 550-556. Revelle, W., Amaral, P. & Turiff, S. Introversion/extraversion, time stress, and caffeine: Effect on verbal performance. Science, 1976, 192, 14~150. Rodnight, E. & Gooch, R. A new method for the determination of individual differences in susceptibility to a depressant drug. H. Eysenck, (Ed.) Experiments with Drugs. Oxford: Pergamon, 1963. Shagass, C. Neurophysiological studies of anxiety and depression. Psychiatric Research Reports, 1957, 8, 100-117. Von Felsinger, J., Lasagna, L. & Beecher, H. Drug-induced mood changes in man: 2. Personality and reactions to drugs. Journal of the American Medical Association, 1955, 157, 1113-1119. Williams, E., Himmelsbach, C., Wikler, A., Ruble, D. & Loyd, B. Studies on marijuana and pyrahexyl compound. Public Health Reports, 1946, 61, 1059-1083. Zinberg, N. & Weil, A. A comparison of marijuana users and non-users. Nature, 1970, 226, 119-123.
0306-460379, I 101-0361$02.00/0
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PERSONALITY CORRELATES OF CANNABIS DEPENDENCE* JOHN BACHMAN a n d REESE T . JONES Langley Porter Neuropsychiatric Institute University of California~ San Francisco
Abstract--The personality characteristics of 48 male volunteers were measured with the M M P I and were related to measures of cannabis withdrawal symptoms. Personality variables accounted for 25~; of the variance in these symptoms. Neurotic introversion, a tendency not to deny anxiety, absence of sensation seeking and openness were traits found to relate positively to the intensity of cannabis abstinence symptoms.
In addition to pharmacological and environmental determinants of psychoactive drug effects, individual differences in personality characteristics influence reactions to a variety of psychoactive drugs (Von Felsinger et al., 1955; Kornetsky & Humphries, 1957; Shagass, 1957; Klerman et al., 1959; Claridge & Herrington, 1960; Lindemann & Von Felsinger, 1961; Rodnight & Gooch, 1963; Nash & Stone, 1974; Claridge, 1976; Revelle et al., 1976; and Capone et al., 1976). None of these studies, however, evaluated the effect of personality on reactivity to cannabis (i.e. marijuana, hashish, THC, etc.). Several reports describe correlations between personality and levels of cannabis usage. However, the cannabis literature contains few studies of how personality differences affect the subjective experience associated with cannabis intoxication (Naditch, 1974), and very few studies which report cannabis abstinence symptoms (Jones et al., 1976). The correlational studies relating personality and cannabis usage were conducted during the last decade with students, drug treatment patients, and people in prisons and labor unions (McAree et al., 1969; Hogan et al., 1970; Zinberg & Weil, 1970; Brill et al., 1971; Harmantz et al., 1972; Knecht et al., 1972). Conceptual and methodological inadequacies limit the generalizability and validity of the findings but the results are consistent and support the hypothesis that different patterns of cannabis use are associated with different profiles on personality tests. Frequent users score higher on test scales indicative of psychopathy (i.e. impulsive, antisocial non-conformity), extraversion, sensation seeking and psychopathology. Infrequent and non-users are less antisocial and alienated but more introverted, controlled, neurotic and concerned with social achievement. These data suggest a corollary hypothesis: the personality characteristics associated with frequent cannabis use predict greater levels of cannabis withdrawal symptomatology and dependence in these people. Evidence for dependence on cannabis requires that a clear-cut and consistent withdrawal syndrome follow a period of its regular use. The syndrome may include signs and symptoms of abstinence alone and may or may not include drug-seeking behavior. Physical and psychological withdrawal symptoms occurring after abrupt cessation of prolonged cannabis intoxication have been reported in laboratory animals (Deneau & Kaymakcalan, 1971; Kaymakcalan et al., 1977) and human subjects (Williams et al., 1946; Jones et al., 1976; Nowlan & Cohen, 1977). In our laboratory (Jones et al., 1976), THC was administered orally every 4 hr in doses that were increased to 30 mg and given for 11-12 days. Tolerance developed to many of the drug's initial effects. When the THC was replaced by placebo pills under double-blind conditions, virtually every subject experienced mood changes, disturbed sleep, decreased appetite, restlessness, irritability, perspiration, chills, feverish feelings, nausea, abdominal distress, tremulousness, weight loss, loose bowel movements, hemoconcentration, sleep EEG eye movement *Research supported by funds from Contract No. HSM-42-73-181 and Grant No. DA01696 from the National Institute on Drug Abuse and Research Scientist Award No. DA00053 to Reese T. Jones, M.D., from the National Institute on Drug Abuse. 361
362
JOHN BACHMAN and REESE T. JONES
rebound, waking EEG changes and increased intraocular pressure. This withdrawal syndrome persisted for 72-96hr with most of the changes returning to pre-drug levels after 5 days. The signs and symptoms were eliminated by administration of smoked or oral doses of cannabis. Cannabis dependence was defined by the appearance of this characteristic withdrawal syndrome. This paper reports an attempt to describe the relationship between personality and variation in responses following the abrupt cessation of prolonged cannabis administration. Personality characteristics of subjects were measured by the Minnesota Multiphasic Personality Inventory (MMPI) and by Eysenck's indicators of extraversion and neuroticism. Subjects' self-reports and nurses' observations of their behavior were used to measure abstinence symptoms. METHOD
Subjects Male subjects with prior cannabis experience were recruited by advertisements in newspapers. Each subject gave his informed consent to participate in this experiment which was approved by the Committee on Human Research of the University of California, San Francisco. Subjects were paid S25.00 for each day of their participation. After thorough screening, 64 healthy and cooperative men were hospitalized and tested for 21-42 day periods. Ages ranged from 20 to 31 yr with a mean of 25 yr. Upon admission into the experiment, their mean body weight was 68.6 kg with a range of from 53.6 to 88.2 kg. Subjects had attended school for an average of 14 yr with a range of from 11 to 18 yr. They reported using marijuana regularly for an average of 5 years with a range of from 1 to 15 yr. During the 3 months prior to their participation in the experiment, they reported using marijuana "nearly every day". These men drank beer or wine on the average of "once or twice a week" and drank whiskey or hard liquor on the average of "about once a month". Many of the subjects used nicotine and caffeine daily. Men with more than infrequent and sporadic hallucinogen, stimulant, barbiturate or opiate use were not included in the experiment. One hundred thirty-three applicants completed Minnesota Multiphasic Personality Inventories (MMPIs) as part of the evaluation used to screen potential subjects. Of these 133 applicants, 64 eventually participated in the experiment. Sixty-nine applicants were excluded from participation on a variety of grounds such as physical illness, excessive polydrug use or leaving San Francisco (i.e. they were not excluded just on the basis of aberrant MMPI profiles). The mean MMPI profiles of (1) all 64 subjects, (2) a subset of 48 subjects included in some of the following analyses, and (3) the 69 excluded applicants are presented in Table 1 and Fig. 1. Forty of 64 subjects completed both M E A N M M P I PROFILES FOR ALL SUBJECTS USED IN THE EXPERIMENT (N : 64) A N D EXCLUDED APPLICANTS (N : 69)
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JOHN BACHMAN and REESE T. JONES Table 2. Mean EPI scale scores for a subset of the subjects in this experiment (N = 40)
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forms of the Eysenck Personality Inventory (EPI; see Eysenck & Eysenck, 1968). The mean (combined) EPI "extraversion" and "neuroticism" scale scores are presented in Table 2. Interpretation of the mean M M P I profiles of these 133 men suggests that as a group they demonstrated (1) aesthetic sensitivity and passivity (i.e. the high Mf--masculine/ feminine--scores); (2) an excessive need for stimulation and excitement (i.e. the elevated M a - - h y p o m a n i a - - s c o r e s ) ; (3) alienated and non-conformist sociopathic tendencies (i.e. the elevated Pd--psychopathic deviant--scores); and (4) an ability to cope and adapt successfully (i.e. the elevated Es---ego strength--scores). The scores on the Eysenck Personality Inventory indicate these subjects were not unlike the group of normative American college students, except they possessed considerably lower neuroticism scores.
Setting The subjects lived 24 hr per day for the entire 21-42 day duration of the experiment on a 24 bed general psychiatric unit. The unit was staffed so as to both treat psychotic patients and conduct a variety of clinical research studies. Usually, 4 research subjects lived on the ward at any given time. Subjects were permitted to leave the ward or receive visitors only when supervised by research or nursing staff. Periodic blood and urine analyses were performed to screen for non-experimental drugs. There was no restriction placed on cigarette or coffee use. Subjects participated in an extensive set of biochemical and electrophysiologic tests and performed several behavioral and cognitive tasks daily, primarily between 7:00a.m. and 5:00p.m. At other times, they were free to sleep, read, play their musical instruments, etc. Of the 48 subjects from whom withdrawal symptom data were collected and analyzed, 8 were hospitalized for 21 days, 34 stayed for 30 days and 6 spent between 35 and 42 days in the hospital.
Experimental treatments During the hospitalization, subjects received single, opaque gelatin capsules that contained from zero to 30 mg of delta-9-tetrahydrocannabinol (THC) every 4 hr. The T H C was administered in the form of either pure T H C dissolved in a sesame oil vehicle or a crude cannabis extract of 29~o THC, 2.8~o cannabidiol and 1.5% cannabinol dissolved in 0.2~).4 c m - 3 of 95~o ethanol vehicle. No differences in the effects produced by these 2 preparations were observed. The doses administered to subjects were determined on the basis of the T H C content only, which was equated between the 2 preparations. These drugs were provided by the National Institute on Drug Abuse and were assayed periodically throughout the study to determine their T H C content. The capsules were given orally under double-blind conditions by a nurse. All subjects were evaluated initially during a 3-7 day baseline, pre-drug period of placebo (i.e. vehicle) administration. After an initial 10--30mg dose of THC, the dose level was increased rapidly (i.e. over 2-3 days for 24 subjects) or slowly (i.e. over 4-6 days for the remaining 24 subjects) to the maximum amount of 30 mg every 4 hr. Thirtyfive subjects received an additional 10-30mg dose at bedtime or at noon. Thus, the total daily dose administered was between 180 and 210 mg of T H C which amounted to an average of 3.1 mg/kg per day. A rough, but commonly accepted estimate of the equivalence between oral vs smoked T H C states that smoked doses are 3 times as
Personality correlates of cannabis dependence
365
"potent" as oral doses. Thus, in Mendelson et al.'s (1974) study of marijuana selfadministration, the "heavy" users smoked an average of 6 cigarettes per day. Each contained approximately 1 g of marijuana and between 18-23 mg of THC. These subjects therefore smoked about 20 mg x 6 cigarettes, or 120 mg of THC daily. But, given that about one-half of the THC present in a cigarette is lost to the smoker in side-stream smoke and between puffs, Mendelson et al.'s subjects more realistically consumed about 60mg of THC per day. This dose compares with the 180-210mg of THC consumed daily by subjects in our experiment when the smoked dose (60mg) is multiplied by 3 to convert from smoked to oral potency. The major difference between the 2 studies is the schedule of dosage administration. In our study, the THC was administered in 30mg doses given orally every 4hr around the clock. Forty-five of the 48 subjects were maintained on the fixed maximum dose for at least 8 days. Following the period of THC administration, subjects were given placebo capsules again for between 3 and 9 days and then discharged. Cessation effects
In order to study the cannabis withdrawal syndrome, the signs and symptoms following the abrupt cessation of THC administration were measured and analyzed. Cessation effects are defined operationally in two ways: (1) as the difference between the mean values of subjective and behavioral ratings made during the first 3 days immediately following cessation of THC administration and (i.e. minus) the last 3 days of maximum dose THC administration; and (2) as the difference between the mean values of subjective and behavioral ratings made during the first 3 post-THC days and (i.e. minus) the last 3 days of the pre-THC baseline. These two definitions of the cessation effect are referred to as CEF 1 and CEF 2, respectively, in what follows. The first definition emphasizes changes in a subject's state that are associated with THC withdrawal and may only reflect the disappearance of drug effects. The second definition of cessation effects, CEF 2, is included to determine if the subjective and behavioral changes associated with the end of a period of prolonged THC intoxication represent simply the disappearance of drug effects and/or the emergence of abstinence and dependence. If the drug effects were wearing off, subjects' reports of intoxication would be expected to return to basal level and no additional subjective phenomena would be expected to occur. If abstinence were evident during the post-THC period, subjects would be expected to report symptoms different from those of intoxication and at values different than the basal level. CEF 1 represents the difference in subjects' states just before and just after withdrawal of THC while CEF 2 reflects the difference in subjects' conditions before and after the entire period of THC administration. Dependent variables
Among the many measures used to evaluate the effects of THC, one set obtained daily for each subject consisted of self-reports and nurses' reports. These were recorded on the Symptom Check List (SCL-90), the Profile of Mood States (POMS) and the Nurses' Observation Scale for Inpatient Evaluation (NOSIE) (Guy, 1976). These instruments were used in this experiment because of their demonstrated sensitivity to other psychoactive drugs and because they permitted quantification and between-subject comparison. A set of SCL-90, POMS and NOSIE scales that reflect the changes following cessation of THC administration were selected on the basis of the results of repeated measures analyses of variance that showed the temporal changes before, during and after drug administration to be statistically significant. Those scales whose mean scores changed significantly from the baseline or maximum dose administration stages to the post-drug stage were considered to reflect CEF 1 and CEF 2. The scales selected to reflect the cessation effect included "hostility" and "sleep disturbance" from the SCL-90, "anger-hostility" from the POMS and "irritability" from the NOSIE. A listing of scores on the selected scales from (1) the final 3 pre-THC days, (2) the last 3 maximum dose days and (3) the first 3 post-THC placebo days was prepared
366
JOHN BACHMAN and REESE T. JONES MEAN
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for each subject. On the basis of this listing, each of the selected scales' scores for each of the 48 subjects on each of the listed days was standardized and combined to yield daily composite z scores for each subject. Mean daily composite z scores were c o m p u t e d by summing all of the subjects' composite z scores on a particular day and dividing the sum by the number of subjects. The mean daily composite z scores for the C E F scales are presented graphically in Fig. 2.
Personality data To reduce the number of personality variables under consideration, 17 M M P I (K-corrected) scale scores contributed by the 133 applicants to the experiment were factor analyzed (see Table 1 for the scale scores). A principal components analysis was performed and those factors with eigenvalues greater than one were rotated via the varimax procedure to obtain an orthogonal solution. Four factors were so formed. Individual factor scores for each of the 48 subjects were computed. Median factor scores for each factor were computed and subjects scoring above or below each median score were identified. RESULTS
Results of the M M P I factor analysis Given the almost parallel and nearly identical profiles between the men accepted into the study and those excluded (see Fig. 1), we decided to combine data oblaincd from all subjects and use the total sample for the factor analysis. Four factors with eigenvalues greater than one were rotated to simple, orthogonal structure. Together. they accounted for 68~o of the total variance. The rotated factor loadings of each scalc on each factor are presented in Table 3. Factor 1 accounted for 30~o of the total variance. Welch's A or "anxiety" scale, Navran's Dy or "dependency" scale, Barron's Es or "ego strength" scale (which loaded negatively), the Si scale, the F scale, the K scale (which loaded negatively), the Sc scale and the Pt scale all loaded at 0.50 or more on factor 1. This factor is quite similar in composition to others found by factor analysis of M M P I scales and has been referred to as dimension of ego-weakness vs ego-strength by Kasselb a u m et al., (1959). They interpreted the factor as one reflecting " . . . m a l a d j u s t m e n t , general neuroticism, anxiety, d e p e n d e n c y . . , as opposed to healthy non-anxious personality, absence of disorders and a tendency towards leadership and intellectual ability" (p. 233).
Personality correlates of cannabis dependence
367
Factor 2 accounted for 18~ of the total variance and, like factor 1, also reflected distress or psychopathology (indicated by the high loadings of Sc and Pt), but of a kind characterized by the denial of anxiety (high K loadings) and the tendency to express distress and conflict via somatic symptoms (high Hs and Hy loadings) or behavior disorders (high Pd loading). Factor 3 accounted for 12~o of the total variance and consisted primarily of Mac Andrew's Mc or "addiction prone" scale, the Ma scale and the D scale (which loaded negatively). This factor reflects a dimension of sensation seeking where individuals scoring +Mc, + M a and - D are characterized by their high energy level, restlessness, enthusiasm, impatience, hyperactivity, cheerfulness, spontaneity and lack of depression.. They tend to seek out and use psychoactive drugs in their pursuit of excitement. Indi-. viduals scoring - M c , - M a and + D on this factor demonstrate a low energy level, non-competitiveness, a lack of self-confidence, depression, worry and pessimism. They usually abstain from excessive psychoactive drug use. Factor 4 accounted for 8~o of the total variance. The Mf scale loaded positively and the L scale loaded negatively on factor 4. Educated, culturally oriented, interpersonally sensitive males who tend to be socially responsive, passive and able to admit minor faults easily tend to have high scores on this factor. The meaning of these four MMPI factors may be elaborated further by noting their relationship with Eysenck's dimension of extraversion/introversion, neuroticism/stability and the EPI lie validity scale. Correlation coefficients between the MMPI factors and the EPI scales are presented in Table 4. Factor 1 correlated negatively with extraversion (r (38) = -0.428, 19 < 0.01) and positively with neuroticism (r (38) = 0.529, /9 < 0.01) which confirms its identity as a factor reflecting neurotic introversion. Factor 2 correlated negatively with neuroticism (r (38) = -0.338, /9 < 0.05) which suggests that subjects scoring high on factor 2 tend to deny anxiety. Factor 3 correlated positively with extraversion (r (38) = 0.565, P < 0.01) which reflects the social ebullience and impulsivity of high factor 3 subjects. And factor 4 correlated positively with neuroticism (r (38) = 0.345, P < 0.05) which suggests the presence of anxiety in high factor 4 subjects. None of the factors correlated significantly with Eysenck's lie scale which suggests the subjects responded truthfully to the MMPI items.
Personality factors and the cessation effect CEF 1 was determined by computing the difference between the mean composite z score of the first 3 post-THC days and the mean z score of the last 3 maximum Table 3. Factor loadings of 17 M M P 1 scales on four M M P I factors derived from a principal components factor analysis with varimax rotation (N = 133) Scale loadings
Scale loadings
Scale loadings
on
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factor 2
factor 3
factor 4
A Dy Es Si F K Sc Pt D Pa Hy L Ma Pd Mc Mf Hs
0.89 0.85 -0.77 0.74 0.70 -0.68 0.60 0.57 0.47 0.32 -0.25 -0.17 0.13 0.11 0.08 0.06 0.00
Hs Hy Sc Pt K Pd Pa D L Ma Es Mc Si F Dy Mf A
0.83 0.80 0.61 0.60 0.56 0.54 0.43 0.38 0.30 0.23 -0.19 -0.14 -0.14 0.13 - 0.09 0.08 -0.04
Mc Ma D Si Pd Hy F Mf Pa L Sc K A Hs Es Pt Dy
0.79 0.77 -0.55 -0.44 0.31 -0.22 0.19 -0.14 0.14 - 0.11 0.11 -0.09 0.08 -0.07 - 0.07 0.02 0.01
Scale loadings
Mf L Pa Dy F Pt Hs A Mc Ma K Es Si D Sc Pd Hy
0.78 -0.51 0.36 0.36 -0.31 0.26 -0.24 0.24 -0.22 0.20 -0.19 0.14 -0.09 0.07 - 0.04 0.04 0.03
368
JOHN BACHMANand REESET. JONES Table 4. Simplecorrelations between the four MMPI factors and the three Eysenck personality scales (N = 40) Extraversion Factor Factor Factor Factor
1 2 3 4
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-0.428* 0.172 0.565* 0.123
Lie
0.529* -0.338t -0.108 0.345t
-0.116 -0.148 -0.185 -0.207
* P < 0.01, 38 d.f.
t P < 0.05, 38 d.f.
dose days. C E F 2 was d e t e r m i n e d by c o m p u t i n g the difference b e t w e e n the m e a n z score of the first 3 p o s t - T H C days a n d the m e a n z score of the last 3 p r e - T H C baseline days. T h e influence of the p e r s o n a l i t y factors o n the subjects' responses to the T H C w i t h d r a w a l was e x a m i n e d (1) b y a m u l t i p l e regression analysis a n d (2) by p l o t t i n g the m e a n c o m p o s i t e z scores for the 3-day periods for C E F 1 a n d C E F 2 for subjects scoring a b o v e or b e l o w the four m e d i a n M M P I factor scores (see T a b l e 5 a n d Fig. 3). T a b l e 5 presents a step-by-step s u m m a r y of the d e v e l o p m e n t of the multiple correl a t i o n s b e t w e e n C E F 1 a n d C E F 2 a n d the four p e r s o n a l i t y factors w h e n these latter variables were e n t e r e d first i n t o the regression e q u a t i o n s . T h e y were e n t e r e d into the e q u a t i o n s in such a n order that each o n e a d d e d a c c o u n t e d for m a x i m u m variance. Together, four p e r s o n a l i t y factors a c c o u n t e d for 25~o of the total variance in b o t h C E F 1 a n d C E F 2. This r e p r e s e n t e d a significant p r o p o r t i o n of the variance (i.e. R z = 0.248, F [4,43] = 3 . 5 4 5 , P < 0 . 0 5 for C E F 1 a n d R 2 = 0 . 2 5 0 , F [4,43] = 3 . 5 9 6 , P < 0 . 0 5 for C E F 2). At the fourth e n t r y step (see T a b l e 5), the partial c o r r e l a t i o n s between C E F 1 a n d factors 3 a n d 1 were significant (i.e. B for factor 3 = - 0 . 2 9 3 a n d B for factor 1 = 0.297; P < 0.05 for both). Also, at the fourth e n t r y step, the partial c o r r e l a t i o n s b e t w e e n C E F 2 a n d factors 4 a n d 3 were significant (i.e. B for factor 4 = 0.332 a n d B for factor 3 = - 0 . 2 8 7 ; P < 0.05 for both). T h e partial c o r r e l a t i o n s b e t w e e n factor 2 a n d C E F 1 a n d C E F 2 were negative b u t n o t significant (P > 0.10) Table 5. Summary of the step-by-step development of the multiple correlation between CEF 1, CEF 2 and the four MMPI personality factors Dependent Variable CEF 1
Step
Factor
1 2
3 3 1 3 1 2 3 1 2 4 4 4 3 4 3 1 4 3 1 2
3 4
CEF 2
1 2 3 4
Multiple R
R2
AR2
F test of R2 F= df=
0.305 0.417
0 . 0 9 3 0.093 4.744t 0 . 1 7 4 0.081 4.752t
1,46 2,45
0.465
0 . 2 1 7 0.043 4.068t
3,44
0.498
0 . 2 4 8 0.031
3.545t
4,43
0.323 0.431
0.104 0.104 0 . 1 8 6 0.082
5.374t 5.161t
1,46 2,45
0.473
0 . 2 2 4 0.038 4.234t
3,44
0.500
0 . 2 5 0 0.026
4,43
3.596t
F test of each B at each step B* F= d.f. = -0.305 -0.290 0.284 -0.306 0.275 - 0.207 - 0.293 0.297 -0.212 0.177 0.323 0.304 -0.286 0.328 - 0.274 0.195 0.332 -0.287 0.188 -0.163
4.744+ 4.557+ 4.409# 5.223t 4.248# 2.404 4.862t 4.951¢ 2.551 1.767 5.375+ 5.108+ 4.535+ 6.000+ 4.243+ 2.122 6.224+ 4.662t 1.998 1.529
refers to Beta, the standardized partial regression coefficient calculated on the final step. t P < 0.05 * B
1,46 1,45 1,45 1,44 1.44 1,44 1,43 1,43 1,43 1,43 1,46 1,45 1,45 1,44 1,44 1,44 1,43 1,43 1,43 1,43
Personality correlates of cannabis dependence
369
M E A N DALLY COMPOSITE Z SCORES FOR THREE DAY PERIODS USED T O C O M P U T E THE TWO CESSATION a
.4
. . . .
SUBJECTS BL mt p
EFFECT SCORES
HIGH
2 mt Mt P
k ~t P
4 ~ Jet P
~ mt P
THREE D A Y PERIODS FOR ALL SUBJECTS A N D FOR SUBJECTS SCORING HIGH &
LOW O N
FOUR MMPI PERSONALITY FACTORS
Fig. 3. Mean composite z scores for 3 day periods used to compute the 2 cessation effect scores. "BL'" refers to the last 3 baseline days and "ML'" refers to the last 3 days subjects received the maximum dose of THC. "P" refers to the 3 days immediately post or following THC administration.
These statistical relationships between the personality factors and the cessation effect are represented graphically in Fig. 3. For each of the factors, there was no difference between the high and low groups' mean composite z scores before T H C withdrawal (i.e. at the points labeled "BL" or baseline and " M L " or last maximum dose days in the figure). The regression analyses showed that the partial correlations between CEF 1 and factors 1 and 3 and between CEF 2 and factors 3 and 4 were significant. Figure 3 shows that subjects with low scores on factor 3 and high scores on factors 1 and 4 reported greater symptom intensities following cessation of T H C administration. F r o m Fig. 3 it can be seen also that subjects with low factor 2 scores tended to report greater changes during the post-drug period. DISCUSSION Subjects reporte d experiencing increased feelings of tension, anger and restlessness along with exhibiting insomnia and anorexia when placebo capsules replaced the active T H C pills. Nurses' observations of increased behavioral activity and irritability corroborated the subjective reports. These changes, which occurred after the abrupt termination of a prolonged period of intoxication during which tolerance developed, may have reflected the disappearance of drug effects and/or the emergence of abstinence phenomena. Two measures of the cessation effect were included in the analyses to distinguish these possibilities. The results clearly show that both measures are greater than zero (see Fig. 3). That is, the level of symptomatic and behavioral changes during the 3 days immediately following T H C withdrawal is greater than both the baseline and last 3 maximum dose days' values. Had the post-drug level of changes been greater than the value of the final 3 drug days but equal to the pre-drug baseline value, it would have been necessary to conclude only that the drug effects were wearing off following its withdrawal. The "overshoot" of the basal values suggests the emergence of abstinence phenomena and thus, by definition, the presence of cannabis dependence. An interesting finding involves the relationship between cannabis dependence and personality. The mean M M P I profile of the experienced cannabis users who applied to and participated in this experiment was characterized by elevated scores on the Mf, Pd and Ma scales. These results are consistent with findings reported previously in the literature (Brill et al., 1971; McGuire & Megargee, 1974; Khavari et al., 1976). However, instead of using just these 3 scales (and hence ignoring the remainder of the M M P I data) and instead of using all of the scales, the entire set of scales was submitted to a factor analysis to produce orthogonal (i.e. uncorrelated) personality factor scores. The factor analysis resulted in the separation of the 3 scales associated with
370
JOHN BACHMANand REESET. JONES
marijuana use. They loaded on factors 4, 2 and 3, respectively, not on a single factor as the mean profile would suggest. This separation suggests that reliance on M M P I scale scores and profiles to infer personality characteristics may tend to distort rather than clarify patterns of personality traits by attributing to every individual a single, c o m m o n pattern. The first M M P I factor that reflected anxiety and general maladjustment and which correlated positively with Eysenck's measures of introversion and neuroticism was positively related to the magnitude of the cessation effect. This suggests that neurotic, introverted individuals who tend to complain about their lives and surroundings not surprisingly are likely to complain more intensely about the changes associated with T H C abstinence. The second personality factor that reflected a tendency to deny anxiety and which correlated negatively with Eysenck's measure of neuroticism was negatively related to the intensity of the symptoms associated with cannabis abstinence. This suggests that strong withdrawal symptoms are reported by men who tend n o t to deny anxiety while reporting increased mood and symptom changes. The third M M P I factor that reflected sensation seeking and which correlated positively with Eysenck's measure of extraversion was negatively related to the magnitude of the cessation effect. This implies that individuals who tend to seek arousal and excitement may tend to experience minimal or diminished sensations associated with T H C abstinence, especially when these are negative in feeling-tone (e.g. increased tension, anger and irritabilty). The hypothesis that the personality characteristics associated with frequent cannabis use predict greater withdrawal symptomatology is partially disconfirmed by this finding that sensation-seeking is negatively correlated with the cessation effect. The positive relationship between the cessation effect and the fourth personality factor which reflected sensitivity and openness and which correlated positively with neuroticism suggests that empathic and honest, although neurotic, men are likely to report the symptoms of cannabis abstinence more intensely. The relationships between the measures of personality and the T H C cessation effect may reflect general response tendencies or behavioral sets that determined these peoples' style of reporting subjective estimates of personality traits and mood states. While the independent behavioral observations made by the nurses were consistent with the selfreports and confirmed the occurrence of change following withdrawal of THC, the predictive value of these personality correlates of cannabis dependence are, at present, merely suggestive. The presence of neurotic introversion, a tendency not to deny anxiety, openness and the absence of sensation seeking in conjunction with regular and frequent cannabis use may predict a greater propensity for individuals with these traits to experience more intense withdrawal symptoms during cannabis abstinence. Whether or not these clusters of personality characteristics are predictive of other aspects of cannabis dependence (e.g. compulsive drug-seeking behavior) is a question for further study.
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