Impact of olanzapine on body weight, body mass index, and waist circumference: A time- and dose–response meta-analysis of randomized controlled trials

Aim This systematic review and meta-analysis evaluated the effects of olanzapine, a second-generation antipsychotic, on body weight (BW), body mass index (BMI), and waist circumference (WC), and examined the influence of dose and treatment duration. Methods PubMed, Embase, Scopus, and Web of Science were searched through June 2025 for randomized controlled trials (RCTs) comparing olanzapine with placebo in adults. Eligible studies reported baseline and follow-up data for BW, BMI, or WC. Pooled weighted mean differences (WMDs) with 95% confidence intervals (CIs) were calculated using random-effects models. Subgroup and dose–response analyses were performed. Results Fifteen RCTs comprising 18 study arms were included. Olanzapine significantly increased BW (16 arms; WMD: 1.72 kg; 95% CI: 0.55–2.88; p = 0.004), BMI (four arms; WMD: 0.84 kg/m 2 ; 95% CI: 0.24–1.43; p = 0.005), and WC (two arms; WMD: 5.79 cm; 95% CI: 1.85–9.73; p = 0.004) versus placebo. Greater effects were observed with doses ≥10 mg/day and treatment durations ≤12 weeks. Participants with baseline BMI <25 kg/m 2 experienced greater weight gain. Dose–response analysis demonstrated increasing weight gain at doses >5 mg/day. Conclusion Olanzapine significantly increases BW, BMI, and central adiposity, particularly at higher doses and during early treatment, highlighting the importance of dose optimization and metabolic monitoring.