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The study, published in Nature Health on the tenth of April twenty twenty-six, analysed more than 410,000 Reddit posts spanning over five years, drawn from roughly 67,000 users who self-reported taking semaglutide or tirzepatide, the active ingredients in drugs marketed as Ozempic, Wegovy, Mounjaro, and Zepbound.
Nearly four percent of users who reported side effects described reproductive symptoms including irregular menstrual cycles, heavy bleeding, and spotting between periods. Others reported chills, hot flushes, and fever-like sensations. Fatigue ranked as the second most common complaint overall despite rarely reaching reporting thresholds in clinical trials.
AI Scans 400,000 Reddit Posts to Uncover Hidden Side Effects of Weight-Loss Drugs
April 13, 2026
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Researchers at the University of Pennsylvania used artificial intelligence to analyse over 410,000 Reddit posts and discovered side effects of popular GLP-1 weight-loss drugs that are largely missing from clinical trials and official drug labels. Reproductive symptoms and temperature-related complaints emerged as two key categories of underreported effects.
AI Meets Social Media in Drug Safety Discovery
A team at the University of Pennsylvania has turned to artificial intelligence and the world's largest online forums to uncover what clinical trials may have missed about the side effects of blockbuster weight-loss drugs.The study, published in Nature Health on the tenth of April twenty twenty-six, analysed more than 410,000 Reddit posts spanning over five years, drawn from roughly 67,000 users who self-reported taking semaglutide or tirzepatide, the active ingredients in drugs marketed as Ozempic, Wegovy, Mounjaro, and Zepbound.
What the Data Revealed
About 43.5 percent of users reported at least one side effect. Gastrointestinal symptoms dominated, with nausea leading at nearly 37 percent, followed by fatigue, vomiting, constipation, and diarrhoea. However, two categories of symptoms stood out for their absence from official adverse-event reports: reproductive issues and temperature-related complaints.Nearly four percent of users who reported side effects described reproductive symptoms including irregular menstrual cycles, heavy bleeding, and spotting between periods. Others reported chills, hot flushes, and fever-like sensations. Fatigue ranked as the second most common complaint overall despite rarely reaching reporting thresholds in clinical trials.
Why It Matters
The researchers used large language models to translate informal patient descriptions into standardised medical terminology at a scale that was previously impossible. While the team stressed the study cannot prove causation, the findings offer new leads for clinicians and regulators. GLP-1 drugs are believed to work by engaging the hypothalamus, which regulates a wide range of hormones, providing a plausible biological mechanism for the reported reproductive and temperature effects.What Comes Next
The team plans to expand the methodology beyond Reddit and beyond English-language communities. As prescriptions for GLP-1 drugs continue to surge worldwide, the pressure on manufacturers Novo Nordisk and Eli Lilly to address these emerging signals is only set to grow.Published April 13, 2026 at 12:13am
