(1) The treatment of obesity is based on calorie reduction and moderate physical activity. (2) Rimonabant, a CB1 cannabinoid receptor antagonist, is marketed in Europe for the adjuvant treatment of obesity, in combination with a low-calorie diet and physical exercise. (3) Four double-blind placebo-controlled trials involving about 6500 patients show that, when combined with a low-calorie diet, rimonabant 20 mg/day leads to an average weight loss of 4 or 5 kg more than placebo after one year of treatment. This is similar to the weight loss reported with orlistat (indirect comparison). Effects on the lipid profile are similar to those reported with sibutramine. (4) Rimonabant has not been shown to reduce morbidity or mortality. Patients regain the weight they lost within about 9 months after rimonabant withdrawal. (5) Three placebo-controlled trials have evaluated rimonabant in smoking cessation. The available results (a single conference abstract) are inconclusive. In early 2006 the FDA and the European Medicines Agency refused to approve rimonabant for this use. (6) Adverse effects mentioned in published clinical trials of rimonabant include mental disorders (anxiety, depression), neurological disorders (dizziness) and gastrointestinal disorders (nausea, diarrhoea). No postmarketing safety data are available. The possible long-term adverse effects of rimonabant are unknown. (7) In practice, when drug therapy is considered for weight loss, it seems unwise to prescribe rimonabant: this new drug has only limited symptomatic effects and its adverse effects, especially in the long term, are poorly documented.