A Cochrane review included 8 studies on naltrexoneat doses of 25 - 100 mg/day reporting long-term abstinence data (six months or more) with over 1200 smokers. All studies were randomized and double-blind and 6 studies confirmed abstinence with biochemical verification (exhaled carbon monoxide or plasma cotinine). There was no significant effect of naltrexone on long-term abstinence (OR 1.26, 95% confidence interval 0.80 to 2.01). No significant difference was detected between naltrexone and placebo (RR 1.00; 95% CI 0.66 to 1.51; n=445), or between naltrexone and placebo as an adjunct to NRT (RR 0.95; 95% CI 0.70 to 1.30; n=768). The estimate was similar when all 8 trials were pooled (RR 0.97; 95% CI 0.76 to 1.24; n=1213).