Int. J. Environ. Res. Public Health 2012, 9 206 placebo quit rate of 21% in a small number of small trials [12]. No intervention was significantly better than placebo. 3.4. Opioids Information was available from five systematic reviews [34-38], four of which were Cochrane reviews. Three reviews included data of six months or longer, and two [37,38] of one to six months. There were a variety of interventions, including psychosocial and pharmacological, mainly methadone or buprenorphine. The reviews mainly used only properly randomised trials in participants with defined opioid addiction, used a mixture of non-use of opioid by measurement or retention in a programme to assess abstinence, and used placebo, or, in one review, maintenance methadone versus tapered withdrawal. There was information on over 2,300 participants with cessation rates over various times. Table 6 shows the main results in terms percentage of abstinent participants with intervention and placebo. For methadone, results are taken from a review [35] reporting true placebo and not contaminated with tapering methadone dose. For psychosocial plus pharmacological interventions, the placebo response included pharmacological interventions and may not be a true placebo, and some of the buprenorphine trials used clonidine as a control. The quit rate with placebo varied between 25% and 50%, with an overall average cessation rate of 43% in 590 participants on true placebo in methadone and buprenorphine trials. A review of psychosocial interventions had a placebo quit rate of 24% in a small number of small trials [12]. Only buprenorphine showed any efficacy in a sensible number of patients, with an NNT of 4.6 (95% CI 3.6 to 6.6). Table 6. Results of opioid cessation reviews, ordered by number of participants. The order is by numbers of participants in the reviews. Intervention is as described in each review, and details of the reviews is in Table 1. Intervention Methadone Buprenorphine Psychosocial plus pharmacological Number of patients 1,135 884 184 Percent abstinent with Active Placebo 48 50 63 41 Relative benefit (95% CI) 1.0 (0.8 to 1.7) 1.7 (1.5 to 2.0) NNT (95% CI) not calculated 4.6 (3.6 to 6.6) 42 25 1.7 (1.1 to 2.6) 6.1 (3.4 to 35) 3.5. Cannabis 4. Discussion The abstinence rate in a single review [12] of mostly short term psychotherapeutic interventions for cannabis dependence was 15% in a small number of small trials. Cessation rates with true placebo in randomised trials using objective measures of abstinence and typically over six months duration were 8% for nicotine, 18% for alcohol, 47% for cocaine, and 43% for opioids. This overview of systematic reviews sought evidence of different quit rates with placebo