A review of psychosocial treatments for substance use disorders looked at 34 diffferent studies into a variety of treatments for drug abusers. Overall the study found that psychosocial treatments had a moderate, positive effect. They were most effective at stopping people using cannabis and least effective when people were abusing a variety of different drugs. The most effective type of treatment was contingency management in which drug users were rewarded when they stopped taking drugs and passed drug tests. Approximately a third of participants dropped out before treatment completion.
Dutra, Lissa ... [et al] - A meta-analytic review of psychosocial interventions for substance use disorders American Journal of Psychiatry February 2008, 14(2), 179-187