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Long-term outcome of treatment for drug dependence
MANAGEMENT
A review of this kind cannot do justice to the considerable literature on longer-term outcomes for drug dependence and the array of programmes studied. The focus here is on large-scale observational studies that have followed samples of patients at one or more points following a baseline intake assessment. There are expectations that treatment will lead to reductions in health problems and improvements in patients’ personal and social situation; consequently, most research studies evaluate treatment on drug-use involvement, health problems and crime. Assessing the recovery profile of someone with drug dependence is complex. Over time, the use of different substances can ebb and flow, as can the individual’s engagement with a treatment system. Interpreting or attributing changes on outcome measures to the specific treatments received can also be challenging since a patient’s social environment and family structure can be influential in supporting or impeding their recovery. Also, almost all observational outcome studies conducted to date cannot unequivocally attribute improvements to treatment. In the absence of a control group of patients randomly assigned to receive no treatment, it is possible that patients would have changed significantly over the same period without specialist care. There have been several published multi-site studies of this kind over the past 30 years, notably in the USA.
Long-term outcome of treatment for drug dependence John Marsden
Prolonged use of psychoactive substances is associated with a range of personal, health, social and legal problems. Drug initiation does not automatically lead to problems and the majority of people who do encounter difficulties experience relatively selflimiting negative consequences during their adolescence and early adulthood, including: • affective symptoms • sleep difficulties • relationship dysfunction • financial and occupational problems. However, a sizeable minority of adults (particularly users of opioids and psychostimulants such as heroin and cocaine) continue to use drugs over many years, and their career of drug-taking is usually punctuated by repeated treatment admissions and relapses. This is not to say that treatment for these problems is unsuccessful, rather that the problem being treated is of a chronic and relapsing nature (McLellan and Marsden, 2003). Although the effectiveness of treatment programmes does vary, there is a consistent finding from outcome studies that levels of patients’ pre-treatment problems (particularly drug use disorders, psychological problems and crime) decline during treatment and then remain lower than baseline levels afterwards. At present, this finding is particularly convincing for investigations of patients with heroin dependence who enter opioid substitution programmes and also patients with heroin or cocaine dependence who are treated in therapeutic communities and other forms of residential rehabilitation.
This contribution summarizes results from selected studies that have investigated recovery over a longer period. These studies generally focus on outcomes from oral methadone substitution treatment and residential rehabilitation programmes. Delineation of what qualifies as ‘long-term’ follow-up is essentially arbitrary, but most studies chosen have follow-ups of between 3 and 5 years. Some studies have investigated outcomes for over a decade after treatment, but this is very rare.
The Drug Abuse Reporting Program (DARP) investigated outcomes at 1, 6 and 12 years for an original base of some 44,000 patients who entered 52 US state-funded methadone maintenance programmes, residential rehabilitation (therapeutic community) programmes, out-patient drug-free (community-based counselling) programmes and detoxification services (Simpson and Sells, 1990). At that time in the USA, the majority of patients entering treatment were dependent heroin users. • At 6-year follow-up, 61% of the DARP sample had stopped taking heroin on a daily basis for at least a full year or longer. Participating in ongoing treatment or returning for subsequent treatment episodes was associated with better outcomes. Of the remaining 39%, around 1 in 5 continued long-term daily opioid use; they were characterized by a chronic pattern of relapsing to heroin use, heavy drinking and prison sentences. • By 12 years, 75% of the sample had not used opioids daily in the past year or longer, and 67% had not used them in the past 3 years (Simpson and Sells, 1990). Time spent in treatment was a major predictor of outcome. Staying in treatment for 90 days or longer was significantly associated with better outcome. Communitybased treatment for opioid addiction was found to be effective in reducing both drug use and criminal behaviours. Overall, patients had an average of over six lifetime treatment admissions (a mean of one admission every 18 months across an average duration of 10 years of drug dependence).
John Marsden is Senior Lecturer in Addictive Behaviour, Division of Psychological Medicine, Institute of Psychiatry, London, UK. His research interests include psychiatric epidemiology, psychometrics, treatment services research and evaluation.
The Treatment Outcome Prospective Study collected data from 11,750 patients admitted to 41 treatment programmes (methadone maintenance, residential rehabilitation programmes and out-patient drug-free counselling services) between 1979 and 1981 (Hubbard et al., 1989). During this time cocaine dependence began to take a more central place among the treatment-seeking population in the USA. After 3–5 years following treatment, for those patients who stayed for at least 3 months in a programme, regular use of heroin reduced by 72% among methadone-treated patients, by
Defining ‘long-term’ outcomes
PSYCHIATRY
47
© 2004 The Medicine Publishing Company Ltd
MANAGEMENT
62% among residential patients and by 47% among those treated in out-patient counselling programmes.
The Drug Abuse Treatment Outcome Study (DATOS): long-term outcomes for cocaine treatment have been reported from the latest major multi-site outcome study in the USA (Simpson et al., 2002). Reflecting the current profile of people seeking treatment in the USA, DATOS has a stronger focus on cocaine dependence than previous studies have had. Follow-up interviews were conducted 1 and 5 years after treatment for 708 patients presenting with cocaine dependence. Weekly cocaine use was reported by 21% at first follow-up and this rose only modestly to 25% at 5 years. Daily alcohol use decreased from 22% before intake to 8% in the fifth year. Illegal activity declined from 40% before intake to 25% after 5 years; arrests in the past year dropped from 34% before intake to 18% in year 5.
The National Treatment Outcome Research Study (NTORS) in the UK used a similar design to the large-scale US investigations and recruited more than 1000 patients from 54 community and residential programmes in England in 1995. The study evaluated four broad types of treatment: • maintenance programmes – a substitute (usually oral methadone) is administered at a suitable and stable level for a period of several months, and sometimes years • reduction programmes – opioid-dependent patients are first stabilized on the substitute and then gradually withdrawn over a period ranging from several weeks to many months • short-term residential programmes lasting 6–12 weeks for people with substance dependence, which include medically supervised withdrawal management (detoxification) as required as a first stage of treatment • longer-term residential programmes, which do not generally provide detoxification and last between 12 weeks and 1 year. A series of paper from NTORS have described outcome results at 6 months, 1 year and 2 years and 4–5-year follow-ups for patients treated in these services (Gossop et al., 1997; 2000; 2001). Figure 1 shows abstinence rates across these points. Among patients treated in methadone programmes, rates of illicit drug injecting fell from 61% at intake to 37% after 4–5 years; among those treated in residential programmes, drug injecting rates dropped from 61% to 29% across the same period.
Mental health problems Many people with drug dependence have co-existing mental health problems, including anxiety and affective disorders, and antisocial and other personality disorders. For example, many patients in NTORS had high levels of psychological health problems at intake to treatment (Marsden et al., 2000a), including thoughts of suicide, and their reports of psychological symptoms were reduced at 1-, 2- and 4–5-year follow-up. In terms of psychiatric health outcomes, outcome studies of dependent opioid and cocaine-abusing patients suggest that, for most patients, psychiatric symptoms improve early on in treatment and that, on average, there are sustained reductions in symptom levels over follow-up (McLellan et al., 1983). It has been found, however, that severe psychiatric symptoms and
Changes in abstinence rates reported by NTORS across 6-month, 1-, 2- and 4–5-year follow-ups for community and residential treatments Measure1
Intake (%)
1 year (%)
2 years (%)
4–5 years (%)
4.3
14.1
24.3
25.7
Heroin
10.9
28.6
36.2
39.1
Non-prescribed benzodiazepines
50.0
63.8
71.7
70.3
Crack cocaine
68.5
79.3
80.1
70.3
Amphetamines
83.0
80.8
83.7
90.2
1.4
33.1
35.9
38.0
Heroin
23.2
46.5
50.0
48.6
Non-prescribed benzodiazepines
40.8
71.1
76.8
73.9
Crack cocaine
66.9
81.0
76.8
71.1
Amphetamines
65.5
83.8
84.5
85.2
Methadone patients (n=276) All drugs
Residential patients (n=142) All drugs
1
Measured as zero drug use in the 90 days before follow-up
1
PSYCHIATRY
48
© 2004 The Medicine Publishing Company Ltd
MANAGEMENT
outcomes. Psychol Addict Behav 1997; 11: 324–37. Gossop M, Marsden J, Stewart D et al. Substance use, health and social problems of service users at 54 drug treatment agencies. Intake data from the National Treatment Outcome Research Study. Br J Psychiatry 1998; 173: 166–71. Gossop M, Marsden J, Stewart D, Kidd T. The National Treatment Outcome Research Study (NTORS): 4–5-year follow-up results. Addiction 2003; 98: 291–303. Gossop M, Marsden J, Stewart D, Rolfe A. Patterns of improvement after methadone treatment: 1-year follow-up results from the National Treatment Outcome Research Study. Drug Alcohol Depend 2000; 60: 275–86. Gossop M, Marsden J, Stewart D, Treacy S. Outcomes after methadone maintenance and methadone reduction treatments: two-year followup results from the National Treatment Outcome Research Study. Drug Alcohol Depend 2001; 62: 255–64. Hser Y I. Drug treatment counselor practices and effectiveness: an examination of the literature and relevant issues in a multilevel framework. Eval Rev 1995; 19: 389–408. Hubbard R L, Marsden M E, Rachal J V, Harwood H J, Cavenaugh E R, Ginzburg H M, eds. Drug Abuse Treatment: A National Study of Effectiveness. Chapel Hill, NC: University of North Carolina Press, 1989. Marsden J, Gossop M, Stewart D, Rolfe A, Farrell M. Psychiatric symptoms among clients seeking treatment for drug dependence. Intake data from the National Treatment Outcome Research Study. Br J Psychiatry 2000a; 176: 285–9. Marsden J, Strang J, with Lavoie D, Abdulrahim D, Hickman M, Scott S. Epidemiologically based needs assessment: drug misuse. In: Stevens A, Rafferty J, eds. Health Care Needs Assessment. Oxford: Radcliffe, 2000b. McLellan A T, Luborsky L, Woody G E, O’Brien C P, Druley K A. Predicting response to alcohol and drug abuse treatment. Role of psychiatric severity. Arch Gen Psychiatry 1983; 40: 620–5. McLellan A T, Marsden J. Contemporary Drug Abuse Treatment: A Review of the Evidence Base. Vienna: United Nations Office on Drugs and Crime, 2003. Simpson D D, Joe G W, Broome K M. A national 5-year follow-up of treatment outcomes for cocaine dependence. Arch Gen Psychiatry 2002; 59: 538–44. Simpson D D, Joe G W, Rowan-Szal G, Greener J. Client engagement and change during drug abuse treatment. J Subst Abuse 1995; 7: 117–34. Simpson D D, Sells S B, eds. Opioid Addiction and Treatment: A 12-year Follow-up. Malabar, FL: Krieger, 1990.
disorders at intake to treatment are a reliable predictor of drop-out and poorer follow-up outcomes (Broome et al., 1999).
Employment Many people with drug abuse problems have enduring difficulties with obtaining and retaining paid employment. Unemployed patients are more likely to drop out of treatment prematurely and to relapse to substance abuse. Although the ability of a treatment programme to secure a job for a client may be limited, community services will usually seek to help a client to improve his or her employment opportunities, and securing or maintaining a job is recognized to be an important goal. Employment has been found to predict retention in treatment and good outcome.
Motivation and engagement Several studies have looked at the extent of patients’ motivation and degree of engagement in treatment. For example, patients who engage early with residential, methadone and counselling programmes stay longer in treatment (Simpson et al., 1995). These findings are supported by work that suggests that improved outcome is generated by counsellors who: • have strong interpersonal and organizational skills • see their patients more frequently • refer to ancillary services as needed • establish a practical therapeutic alliance with their patients (Hser, 1995). Effective treatment must attend to a patient’s multiple needs, including related social, vocational and legal problems. Studies have shown that treatment benefits can diminish rapidly if the patient has poor social and familial supports (Finney and Moos, 1984). Social supports and stresses should be an integral part of the assessment process, and programmes that seek to improve patients’ integration and stability, address life problems, family relationships and personal resources will be valuable.
Conclusion Most treatment studies follow up patients over a relatively short period of time (6 months to 1 year), and longer-term outcome studies are relatively rate. While the picture is far from complete, results from these longer-term studies provide evidence for the effectiveness of treatment for drug dependence, particularly community prescribing interventions and residential care. The combined influence of individual, programme and community factors interact in important ways and influence how a patient reacts to treatment.
REFERENCES Broome K M, Flynn P M, Simpson D D. Psychiatric comorbidity measures as predictors of retention in drug abuse treatment programs. Health Serv Res 1999; 34: 791–806. Finney J W, Moos R H. Environmental assessment and evaluation research: examples from mental health and substance abuse programs. Eval Program Plann 1984; 7: 151–67. Gossop M, Marsden J, Stewart D et al. The National Treatment Outcome Research Study in the United Kingdom: six-month follow-up
PSYCHIATRY
49
© 2004 The Medicine Publishing Company Ltd
A review of this kind cannot do justice to the considerable literature on longer-term outcomes for drug dependence and the array of programmes studied. The focus here is on large-scale observational studies that have followed samples of patients at one or more points following a baseline intake assessment. There are expectations that treatment will lead to reductions in health problems and improvements in patients’ personal and social situation; consequently, most research studies evaluate treatment on drug-use involvement, health problems and crime. Assessing the recovery profile of someone with drug dependence is complex. Over time, the use of different substances can ebb and flow, as can the individual’s engagement with a treatment system. Interpreting or attributing changes on outcome measures to the specific treatments received can also be challenging since a patient’s social environment and family structure can be influential in supporting or impeding their recovery. Also, almost all observational outcome studies conducted to date cannot unequivocally attribute improvements to treatment. In the absence of a control group of patients randomly assigned to receive no treatment, it is possible that patients would have changed significantly over the same period without specialist care. There have been several published multi-site studies of this kind over the past 30 years, notably in the USA.
Long-term outcome of treatment for drug dependence John Marsden
Prolonged use of psychoactive substances is associated with a range of personal, health, social and legal problems. Drug initiation does not automatically lead to problems and the majority of people who do encounter difficulties experience relatively selflimiting negative consequences during their adolescence and early adulthood, including: • affective symptoms • sleep difficulties • relationship dysfunction • financial and occupational problems. However, a sizeable minority of adults (particularly users of opioids and psychostimulants such as heroin and cocaine) continue to use drugs over many years, and their career of drug-taking is usually punctuated by repeated treatment admissions and relapses. This is not to say that treatment for these problems is unsuccessful, rather that the problem being treated is of a chronic and relapsing nature (McLellan and Marsden, 2003). Although the effectiveness of treatment programmes does vary, there is a consistent finding from outcome studies that levels of patients’ pre-treatment problems (particularly drug use disorders, psychological problems and crime) decline during treatment and then remain lower than baseline levels afterwards. At present, this finding is particularly convincing for investigations of patients with heroin dependence who enter opioid substitution programmes and also patients with heroin or cocaine dependence who are treated in therapeutic communities and other forms of residential rehabilitation.
This contribution summarizes results from selected studies that have investigated recovery over a longer period. These studies generally focus on outcomes from oral methadone substitution treatment and residential rehabilitation programmes. Delineation of what qualifies as ‘long-term’ follow-up is essentially arbitrary, but most studies chosen have follow-ups of between 3 and 5 years. Some studies have investigated outcomes for over a decade after treatment, but this is very rare.
The Drug Abuse Reporting Program (DARP) investigated outcomes at 1, 6 and 12 years for an original base of some 44,000 patients who entered 52 US state-funded methadone maintenance programmes, residential rehabilitation (therapeutic community) programmes, out-patient drug-free (community-based counselling) programmes and detoxification services (Simpson and Sells, 1990). At that time in the USA, the majority of patients entering treatment were dependent heroin users. • At 6-year follow-up, 61% of the DARP sample had stopped taking heroin on a daily basis for at least a full year or longer. Participating in ongoing treatment or returning for subsequent treatment episodes was associated with better outcomes. Of the remaining 39%, around 1 in 5 continued long-term daily opioid use; they were characterized by a chronic pattern of relapsing to heroin use, heavy drinking and prison sentences. • By 12 years, 75% of the sample had not used opioids daily in the past year or longer, and 67% had not used them in the past 3 years (Simpson and Sells, 1990). Time spent in treatment was a major predictor of outcome. Staying in treatment for 90 days or longer was significantly associated with better outcome. Communitybased treatment for opioid addiction was found to be effective in reducing both drug use and criminal behaviours. Overall, patients had an average of over six lifetime treatment admissions (a mean of one admission every 18 months across an average duration of 10 years of drug dependence).
John Marsden is Senior Lecturer in Addictive Behaviour, Division of Psychological Medicine, Institute of Psychiatry, London, UK. His research interests include psychiatric epidemiology, psychometrics, treatment services research and evaluation.
The Treatment Outcome Prospective Study collected data from 11,750 patients admitted to 41 treatment programmes (methadone maintenance, residential rehabilitation programmes and out-patient drug-free counselling services) between 1979 and 1981 (Hubbard et al., 1989). During this time cocaine dependence began to take a more central place among the treatment-seeking population in the USA. After 3–5 years following treatment, for those patients who stayed for at least 3 months in a programme, regular use of heroin reduced by 72% among methadone-treated patients, by
Defining ‘long-term’ outcomes
PSYCHIATRY
47
© 2004 The Medicine Publishing Company Ltd
MANAGEMENT
62% among residential patients and by 47% among those treated in out-patient counselling programmes.
The Drug Abuse Treatment Outcome Study (DATOS): long-term outcomes for cocaine treatment have been reported from the latest major multi-site outcome study in the USA (Simpson et al., 2002). Reflecting the current profile of people seeking treatment in the USA, DATOS has a stronger focus on cocaine dependence than previous studies have had. Follow-up interviews were conducted 1 and 5 years after treatment for 708 patients presenting with cocaine dependence. Weekly cocaine use was reported by 21% at first follow-up and this rose only modestly to 25% at 5 years. Daily alcohol use decreased from 22% before intake to 8% in the fifth year. Illegal activity declined from 40% before intake to 25% after 5 years; arrests in the past year dropped from 34% before intake to 18% in year 5.
The National Treatment Outcome Research Study (NTORS) in the UK used a similar design to the large-scale US investigations and recruited more than 1000 patients from 54 community and residential programmes in England in 1995. The study evaluated four broad types of treatment: • maintenance programmes – a substitute (usually oral methadone) is administered at a suitable and stable level for a period of several months, and sometimes years • reduction programmes – opioid-dependent patients are first stabilized on the substitute and then gradually withdrawn over a period ranging from several weeks to many months • short-term residential programmes lasting 6–12 weeks for people with substance dependence, which include medically supervised withdrawal management (detoxification) as required as a first stage of treatment • longer-term residential programmes, which do not generally provide detoxification and last between 12 weeks and 1 year. A series of paper from NTORS have described outcome results at 6 months, 1 year and 2 years and 4–5-year follow-ups for patients treated in these services (Gossop et al., 1997; 2000; 2001). Figure 1 shows abstinence rates across these points. Among patients treated in methadone programmes, rates of illicit drug injecting fell from 61% at intake to 37% after 4–5 years; among those treated in residential programmes, drug injecting rates dropped from 61% to 29% across the same period.
Mental health problems Many people with drug dependence have co-existing mental health problems, including anxiety and affective disorders, and antisocial and other personality disorders. For example, many patients in NTORS had high levels of psychological health problems at intake to treatment (Marsden et al., 2000a), including thoughts of suicide, and their reports of psychological symptoms were reduced at 1-, 2- and 4–5-year follow-up. In terms of psychiatric health outcomes, outcome studies of dependent opioid and cocaine-abusing patients suggest that, for most patients, psychiatric symptoms improve early on in treatment and that, on average, there are sustained reductions in symptom levels over follow-up (McLellan et al., 1983). It has been found, however, that severe psychiatric symptoms and
Changes in abstinence rates reported by NTORS across 6-month, 1-, 2- and 4–5-year follow-ups for community and residential treatments Measure1
Intake (%)
1 year (%)
2 years (%)
4–5 years (%)
4.3
14.1
24.3
25.7
Heroin
10.9
28.6
36.2
39.1
Non-prescribed benzodiazepines
50.0
63.8
71.7
70.3
Crack cocaine
68.5
79.3
80.1
70.3
Amphetamines
83.0
80.8
83.7
90.2
1.4
33.1
35.9
38.0
Heroin
23.2
46.5
50.0
48.6
Non-prescribed benzodiazepines
40.8
71.1
76.8
73.9
Crack cocaine
66.9
81.0
76.8
71.1
Amphetamines
65.5
83.8
84.5
85.2
Methadone patients (n=276) All drugs
Residential patients (n=142) All drugs
1
Measured as zero drug use in the 90 days before follow-up
1
PSYCHIATRY
48
© 2004 The Medicine Publishing Company Ltd
MANAGEMENT
outcomes. Psychol Addict Behav 1997; 11: 324–37. Gossop M, Marsden J, Stewart D et al. Substance use, health and social problems of service users at 54 drug treatment agencies. Intake data from the National Treatment Outcome Research Study. Br J Psychiatry 1998; 173: 166–71. Gossop M, Marsden J, Stewart D, Kidd T. The National Treatment Outcome Research Study (NTORS): 4–5-year follow-up results. Addiction 2003; 98: 291–303. Gossop M, Marsden J, Stewart D, Rolfe A. Patterns of improvement after methadone treatment: 1-year follow-up results from the National Treatment Outcome Research Study. Drug Alcohol Depend 2000; 60: 275–86. Gossop M, Marsden J, Stewart D, Treacy S. Outcomes after methadone maintenance and methadone reduction treatments: two-year followup results from the National Treatment Outcome Research Study. Drug Alcohol Depend 2001; 62: 255–64. Hser Y I. Drug treatment counselor practices and effectiveness: an examination of the literature and relevant issues in a multilevel framework. Eval Rev 1995; 19: 389–408. Hubbard R L, Marsden M E, Rachal J V, Harwood H J, Cavenaugh E R, Ginzburg H M, eds. Drug Abuse Treatment: A National Study of Effectiveness. Chapel Hill, NC: University of North Carolina Press, 1989. Marsden J, Gossop M, Stewart D, Rolfe A, Farrell M. Psychiatric symptoms among clients seeking treatment for drug dependence. Intake data from the National Treatment Outcome Research Study. Br J Psychiatry 2000a; 176: 285–9. Marsden J, Strang J, with Lavoie D, Abdulrahim D, Hickman M, Scott S. Epidemiologically based needs assessment: drug misuse. In: Stevens A, Rafferty J, eds. Health Care Needs Assessment. Oxford: Radcliffe, 2000b. McLellan A T, Luborsky L, Woody G E, O’Brien C P, Druley K A. Predicting response to alcohol and drug abuse treatment. Role of psychiatric severity. Arch Gen Psychiatry 1983; 40: 620–5. McLellan A T, Marsden J. Contemporary Drug Abuse Treatment: A Review of the Evidence Base. Vienna: United Nations Office on Drugs and Crime, 2003. Simpson D D, Joe G W, Broome K M. A national 5-year follow-up of treatment outcomes for cocaine dependence. Arch Gen Psychiatry 2002; 59: 538–44. Simpson D D, Joe G W, Rowan-Szal G, Greener J. Client engagement and change during drug abuse treatment. J Subst Abuse 1995; 7: 117–34. Simpson D D, Sells S B, eds. Opioid Addiction and Treatment: A 12-year Follow-up. Malabar, FL: Krieger, 1990.
disorders at intake to treatment are a reliable predictor of drop-out and poorer follow-up outcomes (Broome et al., 1999).
Employment Many people with drug abuse problems have enduring difficulties with obtaining and retaining paid employment. Unemployed patients are more likely to drop out of treatment prematurely and to relapse to substance abuse. Although the ability of a treatment programme to secure a job for a client may be limited, community services will usually seek to help a client to improve his or her employment opportunities, and securing or maintaining a job is recognized to be an important goal. Employment has been found to predict retention in treatment and good outcome.
Motivation and engagement Several studies have looked at the extent of patients’ motivation and degree of engagement in treatment. For example, patients who engage early with residential, methadone and counselling programmes stay longer in treatment (Simpson et al., 1995). These findings are supported by work that suggests that improved outcome is generated by counsellors who: • have strong interpersonal and organizational skills • see their patients more frequently • refer to ancillary services as needed • establish a practical therapeutic alliance with their patients (Hser, 1995). Effective treatment must attend to a patient’s multiple needs, including related social, vocational and legal problems. Studies have shown that treatment benefits can diminish rapidly if the patient has poor social and familial supports (Finney and Moos, 1984). Social supports and stresses should be an integral part of the assessment process, and programmes that seek to improve patients’ integration and stability, address life problems, family relationships and personal resources will be valuable.
Conclusion Most treatment studies follow up patients over a relatively short period of time (6 months to 1 year), and longer-term outcome studies are relatively rate. While the picture is far from complete, results from these longer-term studies provide evidence for the effectiveness of treatment for drug dependence, particularly community prescribing interventions and residential care. The combined influence of individual, programme and community factors interact in important ways and influence how a patient reacts to treatment.
REFERENCES Broome K M, Flynn P M, Simpson D D. Psychiatric comorbidity measures as predictors of retention in drug abuse treatment programs. Health Serv Res 1999; 34: 791–806. Finney J W, Moos R H. Environmental assessment and evaluation research: examples from mental health and substance abuse programs. Eval Program Plann 1984; 7: 151–67. Gossop M, Marsden J, Stewart D et al. The National Treatment Outcome Research Study in the United Kingdom: six-month follow-up
PSYCHIATRY
49
© 2004 The Medicine Publishing Company Ltd