GLP-1 Drugs for Weight Gain From Antipsychotics: The Trials, the Risks, and How to Ask

Antipsychotic medicines help millions of people live with schizophrenia, bipolar disorder, and other serious mental illnesses. Many of them also cause weight gain, higher blood sugar, and higher blood fats. Over years, those changes raise the risk of diabetes and heart disease. In one Danish trial, the researchers noted that people with schizophrenia die at two to three times the rate of the general population, mostly from heart disease.

GLP-1 drugs are a class of weekly or daily injections that lower appetite and blood sugar. They include liraglutide, semaglutide, and exenatide. Randomized trials have tested them in people taking antipsychotics. The trials found real weight loss, better blood sugar, and no sign that psychiatric symptoms got worse.

No GLP-1 drug is approved for antipsychotic weight gain in particular. But many people taking these medicines meet the standard criteria for a GLP-1 weight-loss drug anyway. The decision is one to make with both your psychiatrist and your primary care clinician. Do not stop or change an antipsychotic on your own.

Not every antipsychotic carries the same risk. The largest comparison to date, a 2020 network meta-analysis in The Lancet Psychiatry, pooled 100 randomized trials with 25,952 people with schizophrenia. A network meta-analysis compares many drugs at once, even ones never tested against each other directly.

Over a median of six weeks, weight change compared with placebo ranged from slightly less than zero for haloperidol to about 3 kg (6.6 pounds) more for clozapine. Olanzapine raised BMI the most. Clozapine caused the largest rises in blood sugar and triglycerides, a type of blood fat. Six weeks is short, and weight gain often keeps building with longer treatment.

The reasons are partly about appetite and partly about metabolism. Many of these drugs block brain receptors that help control hunger, and some affect how the body handles sugar and fat. Some mood stabilizers used in bipolar disorder can also add weight. The point is not to blame the medicine. For many people, clozapine or olanzapine is the drug that keeps their illness under control, and switching carries its own risks.

The best-known trial was run in Denmark and published in JAMA Psychiatry in 2017. It enrolled 103 adults with schizophrenia-spectrum disorders who were taking clozapine or olanzapine, were overweight or had obesity, and had prediabetes. Half got daily liraglutide injections and half got placebo for 16 weeks.

Compared with placebo, liraglutide lowered weight by 5.3 kg (about 12 pounds). It also improved blood sugar: 63.8% of the liraglutide group reached normal glucose tolerance, compared with 16.0% on placebo. Waist size, blood pressure, and LDL cholesterol also improved. The main side effects were stomach-related.

A follow-up one year after the injections stopped found that people had regained some weight. Compared with where they started, the liraglutide group was still 3.8 kg lighter than the placebo group, but blood sugar and blood fats had returned to their starting levels. The benefits faded once the drug stopped, as they do in people without mental illness.

Larger reviews now pool these trials. A 2026 network meta-analysis in JAMA Psychiatry looked at 95 studies of 39 different medicines in about 5,900 people with schizophrenia on antipsychotics. Semaglutide was linked to the most weight loss, about 11 kg more than placebo, based on three trials. Liraglutide followed at about 5.4 kg, then topiramate, metformin, and exenatide at about 3 to 4 kg each. The authors rated the certainty of these estimates as moderate.

This is the question many patients and families ask first. So far, the trial evidence is reassuring.

A 2026 meta-analysis in Translational Psychiatry pooled nine randomized trials with 595 people, most of whom had schizophrenia-spectrum disorders. Compared with control groups, the GLP-1 drugs did not change psychiatric hospitalizations or overall schizophrenia symptoms. A separate 2026 meta-analysis of eight trials with 664 patients in the Journal of Psychopharmacology found no difference in overall or serious side effects, and its authors said the drugs did not compromise psychiatric stability or treatment adherence.

The wider question of mood and suicidal thoughts on GLP-1 drugs has also been studied. In April 2024, the European Medicines Agency's safety committee reviewed trials, safety reports, and large health-record studies and concluded that the evidence does not support a causal link between GLP-1 drugs and suicidal thoughts or actions. Some people do report feeling flat or less interested in things on these drugs; our article on GLP-1 emotional flattening covers what is known. Any change in mood should be reported to your care team right away.

Weight and blood sugar are stand-ins for what matters most, which is fewer heart attacks and longer lives. Trials in people with serious mental illness have not been large or long enough to measure those outcomes.

A health-records study published in October 2026 in the Journal of the American Heart Association offers an early look. Researchers used the TriNetX database to compare 218,043 adults who had a serious mental illness, type 2 diabetes, and obesity and were taking antipsychotics or antidepressants. People who used GLP-1 drugs had lower risks of heart attack, heart failure, and death than matched people who did not. At three years, the absolute differences were 1.0 percentage point for heart attack, 1.8 points for heart failure, and 6.5 points for death.

This kind of study cannot prove that the drugs caused those differences. People who get GLP-1 prescriptions may differ in ways the records do not capture, such as how often they see a doctor. The authors also noted that serious mental illness covers very different conditions and that diagnoses came from billing records.

Stomach problems are the most common side effects of GLP-1 drugs: nausea, vomiting, diarrhea, and constipation. They are usually worst when starting or raising the dose. In the pooled trials of people on antipsychotics, these stomach effects were more common on GLP-1 drugs than on placebo.

Constipation needs extra attention for anyone taking clozapine. In January 2020, the FDA strengthened its warning that constipation caused by clozapine can, in uncommon cases, progress to serious bowel complications that lead to hospitalization or death. The FDA said the risk is higher with other medicines that cause constipation. GLP-1 drugs can also cause constipation, so people on both should tell their care team about any change in bowel habits.

GLP-1 drugs slow how fast the stomach empties. The Wegovy label says this can affect how well other pills are absorbed and advises monitoring the effects of oral medicines taken at the same time. For psychiatric medicines whose blood levels matter, such as clozapine or lithium, ask whether extra monitoring makes sense when you start or change a GLP-1 dose.

Bring both of your clinicians into the conversation. A psychiatrist knows your psychiatric medicines and how stable you are. A primary care clinician or endocrinologist knows the weight-loss drugs, the lab tests, and insurance. Asking them to talk to each other, or bringing notes from one visit to the other, can help.

Questions worth asking:

• Do I meet the criteria for a GLP-1 weight-loss drug, such as a BMI of 30 or higher, or 27 or higher with a related condition like high blood pressure or high cholesterol?
• Is my psychiatric medicine likely contributing to my weight, and is there an equally good option with less weight gain?
• How will we watch for constipation, especially if I take clozapine?
• Should my medicine levels be checked when I start the GLP-1 drug or change the dose?
• What happens to my weight and blood sugar if I stop the GLP-1 drug later?

Coverage depends on the drug's approved uses and your plan. Our guide to which GLP-1 drug is approved for what and our insurance and prior authorization guide explain how plans decide. Because weight tends to return when the drug stops, our maintenance playbook is also worth reading before you start.