Reducing drug use among methadone maintenance clients: Contingent reinforcement for morphine-free urines

Addictive Behaviors, VoL 5, pp. 333-340, 1980 Printed in the USA. All rights reserved.

0306-4603/80/040333-08$02,00/O Copyright 8 1980 Pergamon Press Ltd

REDUCING DRUG USE AMONG METHADONE MAINTENANCE CLIENTS: CONTINGENT REINFORCEMENT FOR MORPHINE-FREE URINES MAXINE L. STITZER” GEORGE E. BIGELOW IRA LIEBSON Departments of Psychiatry, Baltimore City Hospitals and the Johns Hopkins University School of Medicine . Abstract-This study assessed the impact on supplemental heroin use by seven methadone maintenance patients of providing extrinsic reinforcement contingent upon morphine-free urinalysis results. Reinforcement was av@able for morphine-free urine samples during randomly selected weeks. Reinforcement consisted of a choice between $15, two methadone take+ home privileges, and two opportunities to self-regulate methadone dosage. The monetary reinforcer was chosen on 95% of reinforcement occasions. During contingent reinforcement the rate of morphine-positive urinalayses declined significantly below pre-study levels (Wilcoxon Test, P < 0.01). The morphine-positive rate during the randomly intermixed non-reinforcement weeks also declined, and did not differ significantly from that during reinforcement weeks. The post-study morphine-positive rate increased to a level not sign&antly different from the prestudy level. These data suggest generalization of the reinforcement effect to the non-reinforcement weeks, and indicate the need for further studies to determine the specific impact of the reinforcement procedure. Clinically, these data support the utility of contingent reinforcement for drug-free biological samples as a treatment modality for substance abuse.

Methadone maintenance has been the treatment of choice for narcotics dependence for many years, yet there is general agreement in the treatment community that additional therapy is needed to deal with continuing behavioral problems among addict patients (Brill & Chambers, 1973; Dole & Nyswander, 1976; Goldstein, 1976). One persistent behavioral problem apparent among a portion of methadone maintenance patients is continued use of supplemental drugs in addition to methadone. Such continued drug seeking behavior is a defining symptom of drug abuse and one which represents an appropriate and important target for therapeutic intervention. Drug use may be influenced indirectly when therapeutic efforts are focused on the acquisition of skills which result in improved social, personal and emotional adjustment. Alternatively, drug use may be influenced directly by focusing treatment interventions on drug seeking and drug ingestion behaviors. The present study evaluates a direct approach to the treatment of drug abuse, namely the use of contingent reinforcement procedures to promote reductions in drug use. There are ample precedents for the use of operant behavioral approaches and contingent reinforcement procedures in particular in the treatment of substance abuse problems. Several controlled studies have demonstrated the efficacy of contingent reinforcement procedures for promoting reductions in alcohol ingestion (Bigelow et d, 1975; Griffiths et al, 1978; Miller, 1975, Miller et al., 1974) in cigarette smoking (Winett 1973) and in drug abuse (Bigelow et al., 1976; Hall et d, 1977; Stitzer et al., 1978, 1979a). Contingent reinforcement interventions derive from an operant behavioral approach to the analysis and treatment of substance abuse. Such an approach seeks to alter behavior by altering the environmental consequences which maintain and support the behavior. In the present case, environmental consequences of drug use are manipulated by offering positive reinforcement for objective urinalaysis results which reflect reduced drug use. *Send reprint requests to Dr. Maxine Stitzer, Department of Psychiatry, D-S-West, Baltimore City Hospitals, 4940 Eastern Avenue, Baltimore, Maryland 21224.

MAXINE L. STITZER, GEORGE.E. BIGELOW and IRA LIEBSON

334

Table 1. Characteristics of study participants

Client

Age Race (yrs.)

LEG WBD KBU CBT STA LWT DNZ

B B B B B B B

‘Treatment ‘Treatment

33 :: :: :58

Years of narcotics addiction 11 13 6 9 11 11 11

Prior methadone maintenance’ (months) 25 8 3: 0 18 0

Pre-study treatment duration’ (months) 11 14 4 8 4 8 10

Stable methadone dose tmg) 50 60 30 50 30 50 30

at other clinics in present clinic

METHODS

Subjects Seven male methadone maintenance clients participated. All were enrolled in a research clinic and had given their written informed consent to research participation. These clients were selected for the study because they chronically used heroin while enrolled in methadone maintenance. Study eligibility was based on observation of 30% or more morphine positive urine tests in samples collected twice weekly during a 5 week pre-study period. Table 1 shows characteristics of study participants. All were Black, the majority were unemployed, pre-study history of methadone maintenance ranged from 4 to 36 months and maintenance dose of methadone ranged from 30 to 60 mg.

Instructions Prior to the study, eligible clients were notified in writing that they would occasionally be able to earn money or clinic privileges by reducing their heroin use and providing “clean” (morphine free) urine samples. Participants were told that during weeks when contingent incentives were available, these could be earned twice weekly and that for each clean urine provided they could earn one of three items: money, methadone take-home privileges or the chance to regulate their methadone dose for a single day. Clients were encouraged to reduce their drug use during the study in order to earn incentives but were told that they should feel free to reduce drug use as much or as little as they wished since the purpose of the study was to see what people feel like doing when offered choices between drug use and other rewards and privileges.

Procedures Clients generally reported to the clinic seven days in a week and ingested their regular dose of methadone in cherry syrup (Methadose@). All doses were dispensed in a 60 cc volume and were ingested under nursing observation. Urine samples were collected twice weekly throughout the study on Monday and Friday. Sample collection was observed by clinic staff. Urines were analyzed immediately for morphine (opiate test) using an on-site Enzyme Multiplied Immunoassay Technique (EMIT, Syva Corp). In addition, all samples were sent to a commercial lab for routine one dimensional TLC analysis. Samples were routinely analyzed by TLC for methadone, opiates (heroin, morphine, codeine, meperidine, and hydromorphone), quinine (which was not considered in data analyses as evidence of opiate use), barbiturates (phenobarbital, unspecified barbiturates), nonbarbiturate sedatives (meprobamate, methaqualone, glutehimide, ethchlorvynol), stimulants (cocaine, amphetamine, methamphetamine, phenmetrazine) and phenothiazines, phenytoin and propoxyphene. When results on EMIT and TLC differed, TLC

Reducing drug use among methadone clients

335

retests were occasionally performed using a two dimensional TLC analysis. Although contingent reinforcement was based on EMIT results, data reported are those obtained from TLC analysis since EMIT results were not available for all phases of the study. When TLC retests were performed, these retest results were used in data analysis. Weeks during which contingent incentives would be available were randomly selected independently for each client with the following restrictions-( 1) no more than 3 weeks of a given type could occur in succession (2) contingent and non-contingent weeks were equally represented in the final sample of weeks. Clients received written notice on Friday prior to weeks when contingent reinforcement was available but no notices were given for an upcoming week during which no reinforcement was available. Urines were tested immediately after collection and reinforcers, when earned, were distributed immediately after urine test results were obtained. Clients who earned incentives could choose one of the following items: (1) $15.00 cash, (2) two methadone take-home doses (3) the opportunity to self-regulate methadone dose for two single days by as much as f 20 mg. When the take-home option was chosen, clients received two bottles containing their regular dose of methadone. Clients did not have to report to the clinic for the next 2 days and were instructed to take one dose each day at the time they would ordinarily come to the clinic. The dose self-regulation option consisted of two separate opportunities to adjust the stable methadone dose by as much as f 20 mg for a single day. Reinforcers earned had to be used before the next urine test and could not be saved up. Statistics

Percent of morphine-positive urine samples during each experimental condition were sub jetted to analysis by both Wilcoxon Matched Pairs Signed Ranks Test and by the Sign Test. Seven pair-wise comparisons were available for most tests. The following pair-wise comparisons were made: (1) contingent reinforcement vs. no reinforcement (one-tail test), (2) contingent reinforcement vs. pre-study baseline (one-tail test), (3) no reinforcement vs. pre-study baseline (two-tail test), (4) pre-study baseline vs. post-study baseline (two-tail test). RESULTS

Good agreement was obtained between EMIT and TLC results on the opiate (morphine) test, as shown in Table 2. Out of 412 samples tested by both methods, initial agreement was obtained on 90.3% of tests. TLC retests were run on about 25% of initially discrepant results, and concordance was reached for virtually all of the retests. There remained 30 cases where EMIT and TLC outcomes differed (most of these had not been retested on TLC) so that a final overall agreement of 92.7% was achieved in the samples tested on both EMIT and TLC. Figure 1 shows percent of morphine positive urine samples observed in seven individual subjects before and after the study and during reinforcement and no reinforcement weeks within the study period. The figure reveals that 5 of 7 subjects showed marked reductions in morphine positive urine samples during contingent reinforcement weeks as compared to prestudy baseline weeks (LEG, WBD, KBU, ‘CBT, STA), while two subjects (LWT, DNZ) showed

Table 2. Percent of samples1 classified as morphine-positive or morphine negative by two urinalysis methods2 EMIT

TLC

Positive Neaative

Positive

Negative

30.1 4.9

2.4 62.6

‘Total Samples = 412 2Ulinalysis methods were: Multiplied Enzyme Immunoassay Technique (EMIT) and Thin Layer Chromatography (TLC)

336

MAXINE L. STITZER, GEORGE E. BIGELOW and IRA LIEBSON

~_i,~~

a 100 ‘;1

60

2

60

(L ;

40

CBT

20 I: : 2

LWT

I

DNZ

100 80

60 t -

CONTINGENT

REINFORCEMENT

H

NO

REINFORCEMENT

-

L-J

PRE AND POST.STUDY

BASELINE

Fig. 1. Percent morphine positive urine samples are shown for seven individual participants during each phase of the study. Pre- and post-study baseline observations are indicated by open bars. Observations made when contingent reinforcement was available for morphine free urines are indicated by filled bars, while those made when no reinforcement was available are indicated by hatched bars. Number of urine tests included are shown within or immediately above each bar. Urine testing was conducted twice weekly.

little or no reductions in rate of morphine-positive urines. The Wilcoxon Test (N=7) comparing morphine-positive samples during contingent reinforcement and pre-study baseline weeks was significant (P < .Ol). The figure also reveals that rates of morphine positive samples were lower for contingent reinforcement weeks than for no reinforcement weeks in six of seven subjects, the exception being LWT. The Wilcoxon Test (N=7) comparing morphine-positive samples during contingent reinforcement and no reinforcement weeks was not significant, however, while the Sign Test was marginally significant (P < .06). A third relationship apparent in the figure is that rates of morphine-positive samples were generally lower during no reinforcement weeks than during pre-study baseline weeks. This was true for five of seven subjects (LEG, WBD, KBU, CBT, LWT) and the magnitude of reduction in morphine positive tests during no reinforcement weeks was quite striking in most cases. This trend was not sufficiently robust across subjects, however, to be statistically significant. Neither the Wilcoxon Test nor the Sign Test were significant in the comparison between no reinforcement and pre-study weeks. There were no systematic or statistically significant differences in the rate of morphine positive samples during pre-study versus post-study baseline periods. information about relative desirability of the three alternative reinforcers was obtained by examining choices of study participants on occasions when reinforcers were earned. In the

Reducing drug use among methadone clients

,

337

Table 3. Positive urinalysis results other than morphine Percent Positive Urine Samples

Client LEG WBD KBU CBT STA DNZ LWT

Benzodiazepines Baseline’ Study2 -** 26.0 40.0

1.5 11.8 1.4

Cocaine Baseline

Study

10.0 10.0

12.1 11.8

Other drugs Baseline Study.

1.4t 5.0

50.0 37.5

36.8 25.0

lO.Ot 20.0

7.7

2.5* 3.8t

‘pm- and post-study weeks combined 2reinforcement and no reinforcement weeks combined **percent positive urine samples was 0.00 when dash is shown tcodeine-single positive sample *ethchlorvynol-single positive sample

present study, 141 choices were made by the seven study participants. LEG made 25 choices, WBD, 32, KBU, 3 1, CBT, 26, STA, 18, LWT, 6 and DNZ, 3 choices. On 95% of these occasions, study participants chose the money ($15.00) option, while take-home medication was selected on 5% of occasions. Dose self-regulation was never selected by these clients. As shown in Table 3, these study participants characteristically showed few urine positives other than morphine-positives. In three participants (WBD, LEG, LWT) occasional cocaine positives were observed while four participants (WBD, KBU, STA, DNZ) showed occasional benzodiazepine positives. There was no noticeable increase in use of other drugs during portions of the study when heroin use was reduced. DISCUSSION

The present study has shown that an intervention which focuses upon urinalysis test results can have a marked impact on rates of opiate-positive urine samples among a group of methadone maintenance clients. Rates of morphine positive urine samples were substantially reduced in 5 of 7 study participants chosen on the basis of their high pre-study rates of morphine positive urine tests. Evidence for the specific efficacy of a contingent reinforcement intervention, however, is less convincing in the present study. Three participants (LEG, CBT, STA) clearly had lower morphine-positive rates during contingent reinforcement than during no reinforcement study weeks, thus supporting a specific effect of the contingent intervention. On the other hand, dramatic reductions in morphine-positive samples were apparent in all clients during weeks when no reinforcement was available and in two clients (WBD, KBU) no differential effect of contingent reinforcement is apparent. Induction or generalization is one likely explanation for reductions in drug-positive samples during weeks when no reinforcement was available. The random weeks procedure could be viewed as a multiple schedule with reinforcement delivered for clean urines during some weeks and extinction in effect during other weeks. Reductions in drug ingestion generated during contingent reinforcement weeks could generalize by induction to drug ingestion during weeks when contingent reinforcement was not available. From a clinical perspective, these reductions in drug use during no reinforcement weeks might be explained by an “attention placebo” effect. It is well known that positive therapeutic benefit can result from focusing attention on a problem behavior and providing expectations for change. Clearly, further experimentation would be needed to determine the mechanism of observed effects on drug positive urine samples and to determine the relative role of contingent reinforcement per se, scheduling effects and attention placebo effects. Nevertheless, the data from this study demonstrate a clear therapeutic impact on drug use among a population of chronic heroin supplementers as a result of an intervention which included contingent reinforcement for drug-free urine samples. Furthermore, no symptom substitution was observed since reductions in heroin use were not accompanied by increases in use of other drugs (Table 3).

338

MAXINE L. STITZER, GEORGE E. BIGELOW and IRA LIEBSON

To the extent that contingent reinforcement for clean urines was effective in reducing drug use, the findings from the present study support and extend previous findings from this and other laboratories. Stitzer et al. (1979a) for example, have shown that supplemental drug use of methadone maintenance clients can be influenced with contingent reinforcement procedures. In that study, methadone maintenance clients who were chronic users of benzodiazepine drugs dramatically reduced their use of prescribed benzodiazepines at the clinic when methadone take-home privileges were available contingent upon voluntary refusal of prescribed drugs. Few studies have directly examined effects ‘of contingent reinforcement procedures on drug use outside a controlled laboratory or clinic self-administration situation, but data which are available have suggested that these procedures can have a significant impact on drug use. Hall er al. (1977), for example, report a controlled case study very similar to the present study, in which morphine-free urines of a methadone maintenance patient increased dramatically during periods of time when various program privileges and incentives were delivered contingent upon drugfree urine samples. Similarly, Bigelow et al. (1976) present case reports in which use of either opiate or benzodiazepine drugs was influenced by providing reinforcers contingent upon reductions in drug use. Hall et al. (1979), have also examined effects of a monetary contingent incentive program for morphine-free urines in a group of addicts undergoing detoxification from methadone. Clients exposed to the contingent incentive program provided a significantly higher proportion of morphine-free urine samples during detox than did clients exposed to standard clinic treatment. Supplemental drug use is a significant clinical problem among methadone maintenance clients, and enrollees in a maintenance clinic generally include subgroups of clients who are appropriate for therapeutic interventions focused upon supplemental drug use. In spite of the cross tolerance provided by methadone, it has been repeatedly observed from urinalysis test results that a substantial portion of methadone maintenance patients continue to use supplementary opiate drugs in addition to their methadone. Reported program wide rates of opiate positive urine tests (morphine or quinine) have ranged from 10% or less (Harford & Kleber, 1978; Senay et aZ., 1977) to higher rates of 27-38% of tests (Baldridge ef al., 1974; Goldstein et ai, 1977; Tyler & Hargreaves 1975). In analyses of the incidence of drug use, 2040% of patients are commonly reported as showing at least an occasional opiate positive urine test over a period of several months (Goldstein 1972; Bigelow ef al., 1979; Renault 1973), and even higher rates have been reported. Three investigators (Goldstein et al., 1977; Ling et al., 1978; Woody er al., 1975) for example, report that 50-70% of methadone maintenance clients had at least one opiate positive urine during one month or more of urine testing while 33% (Ling er al., 1978) and 57% (Goldstein et al., 1977) had more than 10% of tests opiate positive over several months time. Findings from this clinic are in agreement with previous reports. The seven participants in the present study, who were chronic heroin supplementers, represent about 20% of the total clinic population. Successful application of contingent reinforcement interventions for reduced drug use depends upon the availability of reliable objective measures of drug use which takes place outside the clinic. The on-site EMIT urinalysis system provides an accurate and convenient measure of recent drug use. The on-site system allows for immediate delivery of reinforcers based upon clean urine results and avoids typical delays of one week or more in obtaining urine results when these are sent to an outside laboratory. The relative sensitivity of EMIT testing compared to routine TLC screening depends upon the exact TLC procedure used. Theoretically EMIT and routine single dimensional TLC both detect morphine concentrations of about .5 uglml. EMIT, however, may detect a somewhat higher rate of morphine positives in duplicate samples, as reported by Goldstein et al. (1977) and observed in the present study. It appears from limited data obtained in the present study that discrepancies between TLC and EMIT can be largely eliminated by retesting discrepant samples with a two dimensional TLC analysis. The two dimensioned test allows detection at slightly lower morphine concentrations and improves the ability of TLC to differentiate morphine from other drug metabolites and non-specific urine pigments. In the present study, the relative desirability of three program privileges was assessed by ahowing clients to choose from a three item reinforcer menu when they became eligible by

Reducing drug use among methadone clients

339

providing a drug-free urine specimen during contingent reinforcement weeks. Previous research had identified these three items, methadone take-home privileges, methadone dosage selfregulation and money, as potential reinforcers (Stitzer & Bigelow, 1978; Yen 1974). In two previous studies (Stitzer er (II., 1977, 1979a) methadone take-home privileges had proven efflcacious as reinforcers when used in contingent arrangements, while the reinforcing efficacy of a single day dose self-regulation option was less clear. Methadone maintenance clients took advantage of a single day dose self-regulation option, when this was delivered non-contingently (Stitzer er IIL, 1979b) but the dose self-regulation option proved less effective than take-home privileges in influencing drug ingestion behavior when these two privileges were offered contingent upon reduced drug use within the same experimental protocol (Stitzer er al., 1979a). In the present study, dose regulation emerged as the least desirable reinforcer since this was never selected by these study participants. Even take-home privileges, however, were only selected occasionally, while the cash reward was clearly most desirable among these study participants. The relative desirability of various reinforcer options will probably depend on many factors including the relative magnitude of specific reinforcer parameters (e.g., the value of cash rewards or size of dose increase available), current setting conditions in the clinic and history of the subjects. Thus, our treatment research clinic operates on a seven day per week basis and take-home privileges may have a different status and connotation than in other treatment programs. Although the value of incentive rewards offered in the present program was sufficient to modify drug use in five of seven study participants, it is possible that higher valued reinforcers might have been effective in the two non-responsive participants. The present studies have shown that contingent reinforcement for clean urines can have a therapeutic impact on supplemental drug use among methadone maintenance patients. Although the reliability and specificity of these effects need to be assessed in future studies, these results suggest that it is appropriate and worthwhile to pursue contingent reinforcement strategies in treatment of drug dependence. Furthermore, these results suggest that contingent reinforcement procedures for reducing supplemental drug use can be implemented and evaluated at existing treatment clinics as an adjunct to or substitute for current methods of dealing with the problem of supplemental drug use among methadone maintenance patients. Methadone clinics frequently attempt to influence supplemental drug use by offering program privileges such as take-home medication to clients who are generally well behaved and free of supplemental drug use and by revoking these privileges when drug use occurs (Baldridge et (11, 1974). Unfortunately, this policy is often unsystematic in practice. Take-homes may be based more on “seniority” in the program than on actual behavior, and once privileges are granted, programs find it very difficult to take them away again. A second common policy for dealing with supplemental drug use is to threaten clients who are grievous offenders with expulsion from the program if they do not reduce their drug use. While this policy may result in a lowered incidence of supplemental drug use among the remaining clinic enrollees, there is no information as to whether threats or actual expulsion have any beneficial effect on individual drug using clients exposed to the contingencies. The treatment approach suggested by the present studies involves offering incentives or reinforcement at the treatment clinic contingent upon improved therapeutic outcomes such as reduced supplemental drug use rather than delivering sanctions and punishments contingent upon continued drug use. To the extent that abstinence incentives are effective, this approach provides a rational treatment intervention which will permit patients to experience positive reinforcement within the treatment program contingent upon successful behavior rather than negative, punishing interactions contingent upon misbehavior. Acknowledgement-Supported by USPHS research grant DA 01472 and Research Scientist Development Award DA-00050 from the National Institute on Drug Abuse and approved by the Institutional Review Board for Human Research of Baltimore City Hospitals. We thank the staff of the Behavioral Pharmacology Research Unit clinic for their expert management of clients and study protocols. REFERENCES Baldridge, P., McCormack, hf., Thompson, L., Zarrow, A. & Rimm. B. J. Providing incentives to successful methadone patients. Experimental program. New York State Journal of Medicine, 1974, 74(l), 11 l-l 14.

340

MAXINE L. STITZER, GEORGE E. BIGELOW and IRA LIEBSON

Bigelow, G., Griffiths, R.R. & Liebson, I. Experimental models for the modification of human drug selfadministration: Methodological developments in the study of ethanol self-administration by alcoholics. Fedemtion fioceedings, 1975,34,1785-1792. Bigelow, G., Lawrence, C., Stitzer, M. & Wells, D. Behavioral treatments during outpatient methadone maintenance: A controlled evaluation. Paper presented before the American Psychological Association, Washington, D.C., September, 1976. Bigelow, G., Stitzer, M., Lawrence, L., Krasnegor, N., D’Lugoff, B. & Hawthorne, J. Narcotics addiction treatment: Behavioral methods concurrent with methadone maintenance. Internationul JOWM~ of the Addictions, 1979. In mess. Brill, L. & Chambers, CD. The rationale and design for a multimodality’approach to methadone therapy. In C. D. Chambers & L Brill (Ed&Methadone: Experiences and Issues. *vv. 289-315. New York: Behavioral Publications, 1973. .. Dole, V.P. & Nyswander, M.E. Methadone maintenance treatment. A ten year perspective. Jourmf of the AmericanMedical Association, 1976,235,2117-2119. Goldstein, A. Blind comparison of once-daily and twicedaily dosage schedules ln a methadone program. Clinical PhormacoIogy and Therapeutics, 1972, 13,59-63. Goldstein, A. Herion addiction Sequential treatment employing pharmacologic supports. Archives of General Psychiatry, 1976,33,353-358. Goldstein, A.. Horns, W.H. & Hansteen. R.W. Is on-site urine testing of therapeutic value in a methadone maintenance treatment program? International Journal of the Addictions, 1977, 12,717-728. Grlfflths. R.R., Biaelow. G.E. & Liebson. I. Relationship of social factors to ethanol self-administration in alcoholics, in CE. Nathan, G.A. Marl&t & T. Loberg (Eds.), Alcoholism: New Directions in Behavioral Research and Treatment, pp. 351-379. New York: Plenum Press, 1978. HalI, S.M., Cooper, J.L., Burmaster, S. & Polk, A. Contingency contracting as a therapeutic tool with methadone maintenance clients: Six single subject studies. Behuvior Research and Thempy, 1977, 15, 438441. Hall, SM., Bass, A., Hargreaves, W. & Loeb, P. Contingency management and information feedback in outpatient heroin detoxification. Behuvior Thempy. 1979,10,443451. Harford, R.J. & Kleber, H.D. Comparative validity of random-interval and futed-interval urinalysis schedules. Archives of General Psychiatry, 1978, 35,356-362. Ling, W., Klett, J. & Gillls, R.D. A cooperative clinical study of methadyl acetate. Archives of General Psychirrtry, 1978,35,345-353. Miller, P.M. A behavioral intervention program for chronic public drunkenness offenders. Archives of General Psychiatry, 1975,32,915-918. Miller, P.M., Hersen, M., Eisler, R.M. & Watt, J.G. Contingent reinforcement of lowered blood/alcohol levels ln an outpatient chronic alcoholic. Behavior Research and Therapy, 1974,12,261-263. Renault, P.F. Methadone maintenance: The effect of knowledge of dosage. fnternutionul Journal of the Addictions, 1973,8,41-47. Senay, E.C.. Dorus, W., Goldberg, F. & Thornton, W. Withdrawal from methadone maintenance. Rate of withdrawal and expectation. Archives of Geneml Psychiatry, 1977,34,361-367. Stitzer, M. & Bigelow, G. Contingency management in a methadone maintenance program: Availability of reinforcers. International Journal of the Addictions, 1978, 13, 737-746. Stitzer, M., Bigelow, G., Lawrence, C., Cohen, J., D’Lugoff, B. & Hawthorne, J. Medication take-homes as a reinforcer in a methadone maintenance program. Addictive Behaviors, 1977,2,9-14. Stitzer, M.. Bigelow, G., & Liebson, I. Reinforcement of drug abstinence: A behavioral approach to drug abuse treatment. In N. Krasnegor, (Ed.), Behavioml Approaches to Analysis and Treatment of Substance Abuse. NIDA Research Monograph No. 25, pp 68-90, DHEW Publication No. (ADM) 79-839, Washington, D. C.; U. S. Government Printing Office, 1979. Stitzer, M.L. Bigelow, G.W. & Liebson, I. Reducing benzodiazepine self-administration with contingent reinforcement. Addictive Behaviors, 1979a, 4,245-252. Stitzer, M., Bigelow, G. & Liebson I. Supplementary methadone self-administration among methadone maintenance clients. Addictive behuviors. 1979b, 4, 6166. Tyler, J.C. SCHargreaves, W.H. Treatment sanctions and response to methadone treatment. Paper presented before American Psychological Association, September, 1975. Wlnett, RA. Parameters of deposit contracts in the modification of smoking. Psychological Record, 1973, 23,49-60. Woody, G.E., Mmtz, J., O’Hare, K., O’Brien, C.P., Greenstein, R.A. & Hargrove, E. Diazepam use by patients in a methadone program-how serious a problem? Journal of Psychedelic Drugs, 1975,7,373-379. Yen, S. Availability of activity reinforcers in a drug abuse clinic: A preliminary report. Psychofogical Reports, 1973,34,1021-1022.