• The Effect of Placebo on Weight Loss in Obese Patients: A Meta-analysis

      Slack, Marion; Burke, Eric; Garvin, Matthew; College of Pharmacy, The University of Arizona (The University of Arizona., 2008)
      Objectives: To assess the effect of treatment with placebo on weight loss in obese patients. Methods: The placebo groups from nine orlistat and three sibutramine weight loss studies, as identified from the Padwal meta-analysis, were analyzed for: weight loss in kilograms; change in BMI; type of nutrition and exercise interventions; and bias. The means and standard deviations for weight loss were entered into the Stata meta-analysis program to obtain a forest plot to determine an overall estimate of weight loss. The Potential for Methodological Bias Assessment Tool (PMBAT) was used to create a bias score for each study. Results: Overall, subjects in the placebo group lost 3.8 kg (p<0.001). Placebo subjects in the orlistat trials lost significantly more weight (4.3 kg) than did subjects in the sibutramine trials (1.1 kg, p=0.014). The subjects in the sibutramine studies did not lose a significant amount of weight (p=0.397). There were distinct differences between the sibutramine and orlistat studies with regard to nutrition and exercise interventions. The mean score on the PMBAT was 16.7 ± 3.6; and no study scored higher than 25 out of 45 total points. Conclusions: Overall subjects in the placebo group in the combined orlistat and sibutramine studies lost a significant amount of weight. Differences in study design, bias, and the Hawthorne effect may have contributed to this weight loss.