Drug substitution programmes are designed to control the amount and/or type of drugs consumed by drug-dependent offenders. Some programmes focus upon substituting illegal drugs for legal alternatives (such as methadone), while others legally prescribe drugs such as heroin to prevent users from acquiring them illegally. A reduction in the use of drugs, sometimes down to a total cessation, is assumed to increase the quality of life of the drug user, as well as decrease the their offending. This offending may be in order to gain funds to purchase the drugs, or other related illegal activities such as drug dealing.
This narrative is based on one systematic review of 46 studies, with a second systematic review of 11 studies contributing to the moderator, implementation and economics sections below. The reviews look at the overall effect on offending but do not analyse any effects in terms of different types of crime or crime outcomes, and criminal justice outcomes vary from arrest to charge and conviction of new offences.
Overall, the evidence suggests that drug substitution programmes have reduced crime, but there is some evidence (from only one study, but which reaches statistical significance) that they have increased crime.
When comparing drug substitution programmes, a meta-analysis of five studies of the highest methodological quality showed that prescribing heroin reduced offending significantly more than prescribing methadone.
When comparing drug substitution with other treatments, a meta-analysis of ten studies of high methodological quality showed that methadone prescription reduced offending more than treatments without drug substitution, but the mean effect size was not significant.
However, a meta-analysis of 21 studies of slightly lower methodological quality showed methadone prescription resulted in very large and significant reductions in criminal behaviour compared to pre-treatment levels of offending.
A meta-analysis of three studies of the highest methodological quality showed that buprenorphine does not significantly reduce criminal behaviour compared to methadone or a placebo, although effects are positive showing a small reduction. Two studies of the highest methodological quality showed that naltrexone treatment reduces criminality significantly more than behaviour therapy or counselling. These treatments (buprenorphine and naltrexone) are relatively new and as yet not extensively studied.
The review was sufficiently systematic that many forms of bias that could influence the study conclusions can be ruled out.
The search strategy for the review was well-designed and transparent, with appropriate statistical tests conducted. However it did not take into account any publication bias or unanticipated outcomes.
Some potential biases were identified within some of the primary studies, including small sample sizes and unmatched control groups. However, these were minimal and the review authors only considered studies of the highest study design quality, which were experimental or quasi-experimental in design.
Review 1 suggested a number of ways in which drug substitution programmes might have an effect on offending. It noted that drug addicts are 10 times more likely to be involved in property crimes than non-drug users, so many increasing trends of robbery and burglary in Western countries from 1970 to 1995 may be a side-effect of increasing drug use. Drug substitution aims to reduce drug-related offences as it is assumed that drug addicts commit many offences to finance the purchase of drugs. Therefore criminality will decrease if drugs are supplied to addicts through official channels. This effect should also be seen if drug addicts are given treatments involving substitute drugs (such as methadone) that suppress the physical effects of withdrawal and the immediate need to consume drugs.
Drug substitution programmes also aim to improve the quality of life of drug users by reducing risks of overdose and contagious diseases, by controlling the quality of drugs available to them, preventing marginalisation and improving social integration. Public order problems are assumed to be reduced as addicts acquiring drugs (or substitutes) through official channels should spend less time searching for drugs and concentrating in places where addicts and drug dealers regularly gather. They should also have more time to earn money and resources legitimately.
Review 2 included an analysis to test whether there was a different effect of drug substitution upon offending depending on the setting in which the programme was administered (correctional facilities vs the community). The analysis found that there was no significant impact of the type of setting upon offending. Review 1 did not conduct any analysis of potential differences in contexts.
While Review 1 did not contain any information about implementing drug substitution programmes, Review 2 noted a number of important points. For example, methadone treatment is common in the UK, but the US has generally not endorsed its use, with only 12% of correctional settings in the US offering this option for incarcerated inmates.
The dosage of methadone given to drug addicts varied across studies, and Review 2 suggested that better outcomes may have been seen if higher levels of methadone were given. Low levels of methadone may have compromised study outcomes, and the review suggests that the recommended dosage should be monitored at about 60mg.
One study found that while withdrawal severity can be reduced using slow tapering of temporary substitution drugs, most participants still relapsed into heroin use. One study on oral naltrexone found that in order for treatment to be successful, more supervision was required than is typically available within the criminal justice system. However, for naltrexone the evidence is sparse and this makes it difficult to assess potential problems associated with the different mechanisms of administering the drug (e.g. oral vs implants).
While neither of the reviews conducted a cost-benefit analysis, Review 2 mentioned one prison study which noted that approximately ten times as many inmates can be served with methadone as with buprenorphine with the same staff resources. The authors noted that this is not just seen in correctional facilities, but may also apply in community settings, where physicians have difficulty in obtaining reimbursement for buprenorphine treatment for released inmates, making the continued use of buprenorphine problematic after release.
Overall, the evidence suggests that drug substitution programmes have reduced crime, but there is some evidence from just one study that they have increased crime.
Heroin prescription reduces offending significantly more than methadone prescription. Methadone reduces crime more than treatments without drug substitution, but this reduction is not significant. Studies analysing the effect of buprenorphine and naltrexone both show reductions in crime, but there are too few studies to make definite statements about their effectiveness. More research is required into the contexts in which drug substitution programmes are most effective.
Review 1: Egli, N., Pina, M., Skovbo Christensen, P., Aebi M. F. and Killias, M. (2009) 'Effects of drug substitution programs on offending among drug-addicts', Campbell Systematic Reviews, 2009:3
Review 2: Perry, A. E., Neilson, M., Martyn-St James, M., Glanville, J. M., McCool, R., Duffy, S, Godfrey, C. and Hewitt, C. (2013) 'Pharmacological interventions for drug-using offenders', Cochrane Database of Systematic Reviews 2013, Issue 12
This narrative was prepared by UCL Jill Dando Institute and was co-funded by the College of Policing and the Economic and Social Research Council (ESRC). ESRC Grant title: 'University Consortium for Evidence-Based Crime Reduction'. Grant Ref: ES/L007223/1.