Researchers tracked 70 patients with schizophrenia over 12 weeks to see how antipsychotic medications affected their body weight and fat distribution. They found that patients taking their first antipsychotic medication, especially a drug called olanzapine, gained weight quickly and developed more belly fat. Interestingly, patients who had been on these medications for longer showed stable weight. The study suggests that the early weeks of treatment might be a critical time to monitor weight and prevent long-term health problems like heart disease.

The Quick Take

  • What they studied: How antipsychotic medications affect weight gain and where fat is stored in the body, comparing patients new to these drugs versus those who have taken them for years.
  • Who participated: 70 patients hospitalized in China: 51 were experiencing schizophrenia for the first time, and 19 had chronic schizophrenia. Researchers measured their weight, waist size, and body fat every 4 weeks for 3 months.
  • Key finding: New patients on olanzapine gained about 1.85 kg (4 pounds) every 4 weeks and their waist grew 3 cm (1.2 inches) in the same period. Long-term patients showed stable weight with no significant changes.
  • What it means for you: If you or a loved one is starting antipsychotic treatment, especially olanzapine, expect possible weight gain in the first few months. This is important to discuss with your doctor, who may recommend diet and exercise changes or monitor you more closely. This doesn’t mean you should stop taking medication—the benefits usually outweigh the risks—but awareness helps you prepare.

The Research Details

This was a longitudinal study, meaning researchers followed the same patients over time rather than comparing different groups at one point. They enrolled 70 patients admitted to a hospital in Tianjin, China between January 2023 and June 2024. Researchers measured nine different body composition indicators—including weight, waist size, hip size, and body fat percentage—at the start and then every 4 weeks for 12 weeks total.

The researchers used a statistical method called linear mixed-effects modeling to track how these measurements changed over time. This method is particularly useful because it can handle missing data and accounts for the fact that measurements from the same person are related to each other. They also used standard statistical tests to compare differences between groups.

This research design is important because it captures real changes as they happen, rather than relying on memory or one-time measurements. By measuring patients frequently (every 4 weeks), researchers could detect patterns that might be missed with less frequent check-ins. Separating first-episode patients from chronic patients was crucial because it revealed that the timing of treatment matters—the early phase appears to be when weight gain happens most rapidly.

Strengths: The study measured multiple body composition indicators, not just weight, which gives a more complete picture. Researchers measured patients at regular intervals, reducing reliance on memory. Limitations: The sample size was relatively small (70 patients), which limits how much we can generalize to larger populations. The study only lasted 12 weeks, so we don’t know what happens long-term. The study was conducted in one hospital in China, so results may not apply to other populations. The researchers acknowledge these limitations and call for larger, longer studies to confirm findings.

What the Results Show

In patients experiencing schizophrenia for the first time, nearly all body measurements increased significantly over the 12-week period. Weight increased, BMI (a measure of weight relative to height) increased, waist circumference grew, abdominal fat thickness increased, total body fat increased, and body fat percentage increased. All of these changes were statistically significant, meaning they were unlikely to be due to chance.

The olanzapine group (one of the antipsychotic medications studied) showed the most dramatic changes. These patients gained about 1.85 kg every 4 weeks, their BMI increased by 0.70 kg/m² every 4 weeks, and their waist circumference increased by 3.07 cm every 4 weeks. These steep increases suggest that olanzapine may be particularly associated with weight gain and central obesity (fat accumulation around the belly).

In contrast, patients with chronic schizophrenia (those who had been on these medications for years) showed no significant changes in body composition over the same 12-week period. However, their baseline measurements were already higher than the first-episode patients, suggesting they had already gained weight during their earlier treatment phases.

The researchers used their data to predict when first-episode patients would reach the same body composition levels as chronic patients. They estimated this would take approximately 64 weeks for weight, 42 weeks for BMI, and 28 weeks for waist circumference. Other body composition measures were predicted to reach similar levels within 22 to 68 weeks. These predictions suggest that the rapid weight gain seen in the first 12 weeks, if it continues at the same rate, would lead to substantial long-term changes.

Previous research has documented that antipsychotic medications can cause weight gain, but this study adds important detail by showing that the timing and rate of weight gain varies. The finding that first-episode patients gain weight rapidly while chronic patients show stability suggests that the body may adapt to these medications over time, or that patients may develop better coping strategies. The particular concern about olanzapine aligns with previous studies that have identified this medication as having higher metabolic side effects compared to some alternatives.

The study had several important limitations. First, only 70 patients were included, which is a relatively small number. Larger studies would provide more reliable results. Second, the study only lasted 12 weeks, so we don’t know if weight gain continues at the same rate, slows down, or stops. Third, the study was conducted in one hospital in China, so results may not apply to people in other countries or healthcare settings. Fourth, the researchers didn’t randomly assign patients to different medications—patients were already taking specific drugs when enrolled—so we can’t be completely certain the medications caused the weight gain rather than other factors. Finally, the study didn’t include detailed information about diet, exercise, or other lifestyle factors that could influence weight gain.

The Bottom Line

If you are starting antipsychotic treatment, especially olanzapine: (1) Discuss weight gain risk with your doctor before starting medication—this is important information to have. (2) Plan for regular weight monitoring, ideally every 4 weeks in the first 3 months. (3) Consider starting a healthy diet and exercise routine before or immediately after starting medication, as prevention may be easier than treatment. (4) Talk with your doctor about alternative medications if weight gain becomes problematic, though don’t stop medication without medical guidance. Confidence level: Moderate. This study provides good preliminary evidence, but larger studies are needed for stronger recommendations.

This research is most relevant for: people newly diagnosed with schizophrenia who are starting antipsychotic treatment; family members and caregivers supporting these patients; psychiatrists and mental health professionals prescribing these medications; and people already on antipsychotics who want to understand their weight changes. This research is less relevant for people taking antipsychotics for other conditions (like bipolar disorder) or those already on long-term stable treatment, though some findings may still apply.

Based on this study, expect the most rapid weight gain in the first 3 months of treatment. If weight gain continues at the observed rate, you might reach a new stable weight around 6-15 months into treatment. However, individual responses vary significantly, so some people may gain more or less weight. The good news is that chronic patients in this study showed stable weight, suggesting that weight gain may eventually plateau.

Want to Apply This Research?

  • Track weekly weight and waist circumference measurements. Set a baseline at the start of medication and record measurements every 7 days for the first 12 weeks, then monthly thereafter. Note the specific medication and dose. This creates a clear picture of your personal response pattern.
  • Users starting antipsychotics should: (1) Log daily food intake for the first month to establish baseline eating patterns, then identify one specific dietary change (like reducing sugary drinks or adding vegetables to one meal daily). (2) Set a realistic exercise goal—even 10-minute daily walks count—and log completion. (3) Schedule weekly check-ins with themselves to review weight trends and adjust strategies if needed.
  • Create a dashboard showing weight trend over time with annotations for medication changes, diet changes, or exercise changes. Set alerts if weight increases by more than 2 kg in a 4-week period to prompt discussion with healthcare provider. Compare personal trends to the study’s predicted trajectory to see if you’re tracking faster or slower than average.

This research describes potential side effects of antipsychotic medications but should not discourage their use. Antipsychotic medications are essential treatments for schizophrenia and can be life-changing. Weight gain is a manageable side effect that should be discussed with your psychiatrist, who can help you weigh benefits against risks, monitor your health, and adjust treatment if needed. Never stop or change antipsychotic medication without medical supervision. If you are concerned about weight gain or other side effects, contact your healthcare provider immediately. This summary is for educational purposes and does not replace professional medical advice.