Background: Previous published studies assessed the efficacy of bupropion in smoking cessation only in North American populations of smokers. Results of therapeutic drug trials are not always directly applicable in other populations.

Aims: To confirm the efficacy of bupropion in smoking cessation in European smokers.

Design: A multi-centre, randomized, double-blind placebo-controlled trial.

Setting: Seventy-four smoking cessation out-patient clinics in France.

Participants: The study included 509 smokers motivated to quit smoking. Intervention Subjects were randomized to either slow-release bupropion 150 mg b.i.d. (B) or to placebo (Pl) in a 2 : 1 ratio, treated for 7 weeks, and followed-up for 26 weeks.

Main outcome measure: 6 months' point prevalence abstinence, determined by self-report and expired air carbon monoxide measurement.

Secondary outcome measures: weeks 4-7 and weeks 4-26 continuous abstinence rates, craving, withdrawal symptoms, weight and cigarette consumption in smokers unable to quit. Adverse events were recorded systematically.

Findings: Six months' point prevalence abstinence rates were 31% and 16%[odds ratio = 2.3, confidence interval (CI) 95%: 1.4-3.7] in the B and Pl groups, respectively. Continuous abstinence rates were 41% (B) and 21% (P) with OR = 2.5 (CI 95%: 1.6-3.9) for weeks 4-7, and 25% (B) and 13% (P) with OR = 2.2 (CI 95%: 1.3-3.6) for weeks 4-26, respectively. Craving decreased significantly more with B than with Pl during treatment period, but there was no difference for total withdrawal symptoms score. Abstinent subjects gained significantly less weight at week 7 with B than with Pl. Low level of nicotine dependence, high motivation, absence of smoking-related disease, long duration of previous quit attempts, male gender, low level of current alcohol problems and living as a couple were predictive of successful cessation. With the exception of marital status, no interaction was observed between any of these predictive factors and the efficacy of bupropion. More of those who continued smoking in the B group than the P group reduced their consumption by at least 50%.

Conclusions: Sustained-release bupropion is efficacious as an aid to smoking cessation in European smokers. No outcome predictors were identified that might indicate that certain subgroups of smokers would benefit more than others from treatment with bupropion.