Olanzapine-induced weight gain in patients with bipolar I disorder: a meta-analysis.

OBJECTIVE: The weight impact produced by the atypical antipsychotic olanzapine has been explored in meta-analyses focusing on patients with schizophrenia. However, outcomes identified for schizophrenia patients cannot always be generalized to patients with bipolar disorder. This study aims to quantitatively estimate the impact of olanzapine on the weight of patients with bipolar disorder. DATA SOURCES: EMBASE, Medline, and PsycINFO were searched using the keywords olanzapine AND (bipolar OR acute mania) in conjunction with (weight gain OR weight increase) (last search: October 2010, with no restrictions on dates of publication). English language was used as a restriction. STUDY SELECTION: The search identified 110 articles for review. The inclusion criteria for the chosen studies were a diagnosis of bipolar disorder, the presence of an olanzapine monotherapy group, a comparator placebo or monotherapy group, and mean weight gain and/or incidences of weight gain data. This process identified 13 studies for inclusion. DATA EXTRACTION: The primary outcome measure was the mean weight change between olanzapine monotherapy and comparator monotherapy, reported in kilograms. Standard deviation was extracted directly from studies when possible and imputed for 3 studies. The secondary outcome measure was the reported incidences of ≥ 7% weight gain. DATA SYNTHESIS: The mean difference in weight gain was calculated for the continuous data of the primary outcome. Olanzapine monotherapy was associated with more weight gain when compared to placebo (mean difference = 2.10 kg; 95% CI, 1.16-3.05; P < .001) and other bipolar monotherapy (mean difference = 1.34 kg; 95% CI, 0.95-1.72; P < .001). Odds ratio analysis of the dichotomous secondary outcome also showed more weight gain with olanzapine monotherapy compared to placebo (odds ratio [OR] = 10.12; 95% CI, 1.93-53.14; P = .006) and other bipolar monotherapy (OR = 2.09; 95% CI, 1.27-3.44; P = .004). CONCLUSIONS: Currently available data suggest that olanzapine is associated with significant weight gain in bipolar patients. Issues related to side effect profiles and their impact on treatment compliance and physical health outcomes need to be considered when selecting pharmacotherapy.