BACKGROUND: No pharmacotherapies have been shown to increase long-term (> or = 6 months) tobacco abstinence rates among smokeless tobacco (ST) users. Bupropion SR has demonstrated potential efficacy for ST users in pilot studies. We conducted a multicenter, randomized, double-blind, placebo-controlled, clinical trial to assess the efficacy and safety of bupropion SR for tobacco abstinence among ST users. METHODS: Adult ST users were randomized to bupropion SR titrated to 150 mg twice daily (N=113) or placebo (N=112) for 12 weeks plus behavioral intervention. The primary endpoint was the 7-day point-prevalence tobacco abstinence rate at week 12. Secondary outcomes included prolonged and continuous tobacco abstinence rates, craving and nicotine withdrawal, and weight gain. RESULTS: The 7-day point-prevalence tobacco abstinence rates did not differ between bupropion SR and placebo at the end treatment (53.1% versus 46.4%; odds ratio (OR) 1.3; p=0.301). The 7-day point-prevalence abstinence did not differ at weeks 24 and 52. The prolonged and continuous tobacco abstinence rates did not differ at weeks 12, 24, and 52. A time-by-treatment interaction was observed in craving over time with greater decreases in the bupropion SR group. At 12 weeks, the mean (+/-S.D.) weight change from baseline among abstinent subjects was an increase of 1.7 (+/-2.9)kg for the bupropion SR group compared to 3.2 (+/-2.7)kg for placebo (p=0.005). CONCLUSIONS: Bupropion SR did not significantly increase tobacco abstinence rates among ST users, but it significantly decreased craving and weight gain over the treatment period.