The effectiveness of pharmaceutical interventions for obesity: weight loss with orlistat and sibutramine in a United Kingdom population-based cohort.

AIMS: Drug treatments for obesity have proven efficacy from randomized trials, but their effectiveness in routine clinical practice is unknown. We assessed the effects on weight and body mass index (BMI) of orlistat and sibutramine when delivered in routine primary care. METHODS: We used United Kingdom data from the Clinical Practice Research Datalink to estimate the effects of orlistat or sibutramine on weight and BMI over 3 years following treatment initiation. For comparison, we matched each patient with up to five obese patients receiving neither drug. Mixed effects linear regression with splines was used to model change in weight and BMI. Mean change with 95% confidence intervals (CI) was estimated. RESULTS: We identified 100 701 patients receiving orlistat, 15 355 receiving sibutramine and 508 140 non-intervention patients, with body mass index of 37.2, 36.6 and 33.2 kg m(-2) , respectively. Patients receiving orlistat lost, on average, 0.94 kg month(-1) (0.93 to 0.95) over the first 4 months. Weight gain then occurred, although weight remained slightly below baseline at 3 years. Patients receiving sibutramine lost, 1.28 kg month(-1) (1.26 to 1.30) over the first 4 months, but by 3 years had exceeded baseline weight. Non-intervention patients had slight increases in weight throughout the 3 year period, with gains ranging between 0.01 and 0.06 kg month(-1) . CONCLUSIONS: Orlistat and sibutramine had early effects on weight loss, not sustained over 3 years. As new treatments for obesity are approved, their effectiveness should be measured in routine clinical practice, as effectiveness may be considerably less than seen in randomized trials.