"Government policies have only limited impact on rates of drug use itself. However policies are highly relevant because they can have significant impacts on the levels of drug-related harm. There is now a great deal of international research showing significant reduction in lifetime drug use among drug users who receive treatment and substantial reductions in both crime and health risk behaviours, especially during the treatment episode. Harm reduction initiatives, notably needle exchange and opiate substitution, reduce HIV risk behaviours – to the benefit of both individuals and society. Some research shows that particular kinds of enforcement can reduce the openness and disorder around the distribution of drugs, an important source of harms."

Source

Reuter, Peter and Stevens, Alex, "An Analysis of UK Drug Policy: A Monograph Prepared for the UK Drug Policy Commission," UK Drug Policy Commission (London, United Kingdom: April 2007), p. 83.
http://kar.kent.ac.uk/13332/1…