Antipsychotic Weight Gain: Which Drugs Cause It and What Helps

Creator: Ryan S. Sultan, MD
Published: 2026-11-12

By Ryan S. Sultan, MD
Psychiatrist · Columbia University Irving Medical Center
Published November 12, 2026 · 6-minute read

Weight gain differs widely from one antipsychotic to another. In a network meta-analysis of 100 randomized trials with 25,952 patients and a median treatment duration of 6 weeks, the mean difference from placebo ranged from -0.23 kg for haloperidol to 3.01 kg for clozapine.¹

A second network meta-analysis, of trials lasting 3 to 13 weeks in adults with multi-episode schizophrenia, had weight data for 28,317 participants. Its range ran from -0.16 kg for ziprasidone to 3.21 kg for zotepine.² Both figures are short-term differences from placebo.

Which antipsychotics cause the least weight gain

In its weight analysis of 83 trials, the first network meta-analysis found no evidence of weight gain compared with placebo for ziprasidone, haloperidol, fluphenazine, aripiprazole, lurasidone, cariprazine, amisulpride, or flupenthixol. It found evidence of weight gain with brexpiprazole, risperidone and paliperidone, quetiapine, iloperidone, sertindole, olanzapine, zotepine, and clozapine. The authors rated the certainty of evidence low or very low in 140 of 154 comparisons (91%).¹

Clozapine has its own page on clozapine weight gain.

How much weight people gain on olanzapine

In the olanzapine label's analysis of 13 placebo-controlled studies with a median exposure of 6 weeks, patients on olanzapine gained an average of 2.6 kg while patients on placebo lost 0.3 kg. In studies of at least 48 weeks, the mean gain was 5.6 kg, and 64% of patients gained at least 7% of their baseline weight.³

Weight gain in young and first-episode patients

A nonrandomized cohort study enrolled 338 youths aged 4 to 19 who had taken an antipsychotic for 1 week or less. Of the 272 with at least one follow-up assessment, 30.1% had schizophrenia-spectrum disorders, and the rest had mood-spectrum or disruptive or aggressive behavior disorders. After a median of 10.8 weeks, weight had increased by 8.5 kg with olanzapine, 6.1 kg with quetiapine, 5.3 kg with risperidone, and 4.4 kg with aripiprazole, compared with 0.2 kg in an untreated comparison group of 15.⁴

In a meta-analysis of 28 articles on first-episode psychosis, mean weight gain compared with placebo was 3.22 kg in the short term (12 weeks or less) and 5.30 kg in the long term (13 to 52 weeks). The placebo figures came from a study of outpatients with prodromal symptoms, because the authors knew of no placebo-controlled study in first-episode patients.⁵

The metformin guideline is about prevention, on low-certainty evidence

A 2025 guideline recommends starting metformin together with olanzapine or clozapine. For quetiapine, paliperidone, or risperidone, it recommends the same when the patient has one or more cardiometabolic risk factors or is aged 10 to 25. With any antipsychotic, it recommends metformin if weight rises more than 3% above baseline during the first year.⁶

The guideline concerns preventing weight gain. Its headline figure, 4.03 kg less gain than controls (95% CI 2.28 to 5.78), comes from four randomized trials with 131 participants taking risperidone or olanzapine, and the authors state that the certainty of the evidence is low. They also recommend that lifestyle and diet interventions always be offered wherever metformin is offered.⁶

Metformin has also been tested in people who are already overweight. A 16-week trial randomized 148 overweight outpatients with schizophrenia or schizoaffective disorder, and weight fell 2.0 kg more with metformin than with placebo.⁷ Whether metformin fits a given patient is the prescriber's decision.

Three semaglutide trials enrolled 154, 73, and 31 people

HISTORI randomized 154 patients with schizophrenia, prediabetes, and overweight or obesity who were taking a second-generation antipsychotic. The primary outcome was change in HbA1c over 30 weeks. Compared with placebo, semaglutide reduced HbA1c by 0.46% and body weight by 9.21 kg, with no significant effect on symptom scores.⁸
A 26-week trial randomized 73 people who had started clozapine or olanzapine within the past 5 years. The primary outcome was again HbA1c. Weight fell 9.2 kg more with semaglutide, and psychiatric symptoms did not differ between groups.⁹
COaST randomized 31 people on clozapine, with percentage weight change at 36 weeks as its primary outcome. Body weight fell 13.88% with semaglutide and 0.42% with placebo.¹⁰

The largest of these trials had 154 participants and the longest ran 36 weeks.

Switching trials showed modest weight loss and more discontinuation

A Cochrane review included four studies with 636 participants, with weight loss among its primary outcomes. In two trials with 287 people, switching from olanzapine to aripiprazole or quetiapine was followed by a mean weight loss of 1.94 kg, with a confidence interval of -3.9 to 0.08 that includes no difference. People who stayed on olanzapine were less likely to leave the study early.¹¹

The CAMP trial assigned 109 patients to switch from olanzapine, quetiapine, or risperidone to aripiprazole and 106 to stay on their medication for 24 weeks. Its primary outcome was non-HDL cholesterol. Switching was associated with larger weight reductions (least squares mean 2.9 kg), and 43.9% of switchers stopped the assigned drug before 24 weeks, compared with 24.5% of those who stayed. Efficacy failure occurred in 20.6% and 17.0%.¹² A switch is a decision made with the prescriber.

Two lifestyle trials found weight loss at 6 to 18 months, and one found none

ACHIEVE randomized 291 people with serious mental illness, 58.1% of them with schizophrenia or schizoaffective disorder. At 18 months the intervention group had lost 3.2 kg more than the control group, and 37.8% of the intervention group had lost 5% or more of their weight, compared with 22.7% of controls.¹³

STRIDE randomized 200 people taking antipsychotics. Intervention participants lost 4.4 kg more than controls at 6 months and 2.6 kg more at 12 months.¹⁴ At 24 months they had lost 3.7% of baseline weight and controls 2.1%, a difference that was no longer significant.¹⁵ The 12-month CHANGE trial, in 428 patients with schizophrenia-spectrum disorders and abdominal obesity, found no effect on weight.¹⁶

How often weight and blood tests are checked

The UK's NICE guideline on psychosis and schizophrenia in adults calls for monitoring throughout antipsychotic treatment: weight weekly for the first 6 weeks, then at 12 weeks, at 1 year, and annually. It lists fasting blood glucose or HbA1c and blood lipids at 12 weeks, at 1 year, and annually, and waist circumference annually.¹⁷ The US olanzapine label states that patients should receive regular monitoring of weight.³

Limitations of the evidence

This evidence has limitations. First, both network meta-analyses pooled short trials, and per-drug values are not given on this page. Second, the metformin, semaglutide, and switching trials measured weight and laboratory values over weeks to months. Nevertheless, the differences between drugs appear within weeks, so weight is worth tracking from the first prescription and raising with the prescriber early.

Frequently asked questions

Which antipsychotic causes the least weight gain?

In a network meta-analysis of short trials, the 83 with weight data showed no evidence of weight gain compared with placebo for ziprasidone, haloperidol, fluphenazine, aripiprazole, lurasidone, cariprazine, amisulpride, or flupenthixol. The certainty of evidence was low or very low in 91% of comparisons.¹

Does Abilify cause weight gain?

In short schizophrenia trials, aripiprazole showed no evidence of weight gain compared with placebo. In a nonrandomized cohort of youths aged 4 to 19 taking an antipsychotic for the first time, weight increased by 4.4 kg after a median of 10.8 weeks on aripiprazole.^{1, 4}

How much weight do people gain on olanzapine?

In the olanzapine label, patients gained an average of 2.6 kg over a median of 6 weeks while patients on placebo lost 0.3 kg. In studies of at least 48 weeks the mean gain was 5.6 kg, and 64% of patients gained at least 7% of their baseline weight.³

Does metformin help with antipsychotic weight gain?

A 2025 guideline recommends starting metformin together with olanzapine or clozapine to prevent weight gain. Its figure of 4.03 kg less gain comes from four trials with 131 participants, and the authors rate the certainty low. The decision belongs to the prescriber.⁶

Can Ozempic help with weight gain from antipsychotics?

Semaglutide has been tested in randomized trials of 154, 73, and 31 people. In the largest, it reduced body weight by 9.21 kg more than placebo over 30 weeks with no significant effect on symptom scores. The longest trial ran 36 weeks, and the decision belongs to the prescriber.^{8, 9, 10}

In a crisis: call or text 988, or go to the nearest emergency department. A first episode of psychosis belongs in a hospital-based or coordinated specialty care program.

I start and manage clozapine in an outpatient practice in Chelsea, Manhattan. Details are on the schizophrenia care in NYC page. Clozapine should not be stopped, skipped, or restarted without the prescriber. This page is general information and does not replace an evaluation.