By Dr. Françoise Dubois-Arber, Consultation Event Drug Panel Presenter; Institute of Social and Preventive Medicine (IUMSP), Faculty of Biology & Medicine, Lausanne University Hospital, Switzerland.

Debates on programmes and policies related to illicit drugs – at national or international level – are often difficult, emotional, and not driven by scientific evidence. However, over the last decades, there has been a lot of effort to conduct sound evaluation of programmes and policies and to review the available evidence of effectiveness. The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) provides on its website a review of the evidence of effectiveness of various programmes related to illicit drug use ( The level of evidence regarding prevention, substitution therapy, and harm reduction is briefly summarised here.


The evidence appears “patchy”: not all types of preventive activities and possible outcomes have been systematically assessed. For example, there is no consistent evidence that one of the frequently used types of prevention – i.e. mass media campaigns – is effective1 in modifying illicit drug use – if used alone. On the other hand, comprehensive family-oriented prevention is likely to be beneficial to reduce cannabis use, according to a Cochrane review2.

Several types of school-based interventions are classified by EMCDDA as beneficial or likely to be beneficial in reducing or delaying substance use: those using the concept of social influence and life skills3, and those using peer-led approaches4. Interventions focused only on the improvement of students’ knowledge on drugs have no effect on illicit drug use5. Comprehensive community-based programmes involving community, school and family have been proven to be beneficial in preventing or reducing illicit drug use6.


There is no conclusive evidence at the moment regarding the treatment of cocaine addiction. The effectiveness of pharmacological treatment with antipsychotic drugs, anticonvulsivants or psychostimulants is still unknown. Some other pharmacological approaches (for example with antidepressants or dopamine agonists) or cognitive / behavioural psychosocial interventions7 are likely to be beneficial.

The situation regarding treatment of heroin addiction is completely different: there is compelling evidence of effectiveness for diverse types of treatments. Maintenance treatments with methadone or buprenorphine are beneficial regarding retention in treatment, reduction of opioid use, HIV infection acquisition and mortality8. Psycho-social interventions and case management added to maintenance treatment are also beneficial. Maintenance treatments for pregnant women are considered likely to be beneficial9.

Regarding heroin maintenance treatment for patients in whom methadone maintenance has failed, there is a more balanced evidence with a trade-off between benefits in terms of retention in treatment, reduction of criminal activity, mortality reduction and possible side-effects of treatment10. The effectiveness of therapeutic communities for the treatment of drug misuse and dependence is still unknown11.

Harm reduction interventions

The status of evidence regarding harm reduction interventions is mixed. Many interventions are directed to vulnerable populations, most of them active drug consumers, and they operate in low-threshold settings where protection of anonymity is the rule. Research in these types of settings is difficult, especially experimental research able to bring the highest level of evidence, such as randomised controlled trials. There has been, nevertheless, a lot of observational research and research reviews in these settings and populations, bringing enough evidence to make decisions. The following interventions are now considered likely to be beneficial:

  • Needle/syringe exchange programmes: to reduce injecting risk behaviour and HIV infection12;
  • Drug consumption rooms : to reduce injecting risk behaviour13;
  • Ensuring continuity of treatment from prison to community: to reduce mortality12; &
  • Combination of oral substitution treatments and needle/syringe exchange programmes: to reduce HIV/HCV incidence14.

Beyond evidence

The evidence reported here comes mostly from experimental studies conducted in specific contexts. They give information on efficacy (i.e: the intervention works in an experimental context), less on effectiveness (i.e: the intervention can work in the real, ordinary world in the context of “normal” implementation). In the real world, the intensity and quality of a given programme may vary, the coverage of the target population may also be unequal on a given territory. This may reduce the size of the effect of the intervention. Monitoring the implementation (intensity, quality and coverage) of interventions is therefore important.

In the real world, interventions meant to reduce drug related problems are generally not unique nor independent. Combination of programmes may show results where a single programme does not, provided that a certain degree of coherence between programmes exists. Comprehensive and coherent drug policies have an increased potential for effectiveness ( Randomised controlled trials are generally not relevant to evaluate complex policies: comprehensive evaluation, using many sources of information that can be triangulated to explore proofs of effectiveness, are necessary. These sources of information (specific surveys, routine statistics such as drug treatment statistics, mortality statistics, police and justice statistics, etc.) and other types of data, have to be combined, with a transversal and longitudinal view. In this case we can speak of accumulating or cumulative evidence.

As an example, in Switzerland, a comprehensive continuous evaluation of the national drug policy was set up in 1991 and followed up until 200315. Many studies were set up, some of them repeated over time. This new harm reduction policy was under close scrutiny for political reasons. Progressively, over years, there was convergent and cumulative evidence from the evaluation that:

  • Sale/distribution of syringes was well accepted by the population (87% in favour) (1991);
  • The harm reduction policy did not deter injecting drug users for entering treatment (1991);
  • There was a decrease in the number of new HIV cases among IDU (since 1992);
  • There was a decrease in needle sharing and stabilisation at a low level (since 1994);
  • No increase in injecting behaviour was observed: stabilisation in syringe demand occurred, followed by a decrease (1996); &
  • Coverage of syringes remained high, risk behaviours and HIV incidence low, over time (2009)16, 17.

In conclusion, this accumulated evidence brought by a continuous evaluation was particularly useful to pacify political debates, and contributed to consolidate and maintain a firm and effective harm reduction policy.

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7) Knapp WP, Soares B, Farrell M, Silva de Lima M. Psychosocial interventions for cocaine and psychostimulant amphetamines related disorders: John Wiley & Sons, Ltd., 2007.
8) World Health Organization. Guidelines for the psychosocially assisted pharmacological treatment of opioid dependence. Geneva: WHO, 2009.
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10) Ferri M, Davoli M, Perucci CA. Heroin maintenance for chronic heroin-dependent individuals: John Wiley & Sons, Ltd., 2011.
11) Smith LA, Gates S, Foxcroft D. Therapeutic communities for substance related disorder: Published by John Wiley & Sons, Ltd., 2006.
12) European Monitoring Centre for Drugs and Drug Addiction. Harm reduction: evidence, impacts and challenges. Lisbon: EMCDDA, 2010.
13) Hedrich D, Kerr T, Dubois-Arber F. Drug consumption facilities in Europe and beyond. In: Rhodes THD, editor. Harm reduction: evidence, impacts and challenges. Luxembourg: Publications Office of the European Union, 2010:305-331.
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17) Dubois-Arber F, Balthasar H, Huissoud T, Zobel F, Arnaud S, Samitca S, et al. Trends in drug consumption and risk of transmission of HIV and hepatitis C virus among injecting drug users in Switzerland, 1993-2006. Euro Surveill. 2008;13(21):1-6.