Penn Study Published in Nature Health Flags GLP-1 Symptoms for Further Study

A University of Pennsylvania study newly published in Nature Health used AI to analyze more than 400,000 Reddit posts about semaglutide and tirzepatide. The researchers found recurring reports of menstrual changes, temperature symptoms and fatigue that may deserve more study, but said the posts do not show that the medicines caused them.

A large archive of unprompted reports

The study examined discussions of semaglutide products, including Ozempic, Wegovy and Rybelsus, alongside tirzepatide products Mounjaro and Zepbound. Its underlying dataset contained 410,198 posts from May 2019 through June 2025; researchers identified 67,008 users who said they were taking one of the medications.

People do not generally describe symptoms in medical terminology. The team used large language models to identify self-reported medicine use and side effects, then map informal descriptions to MedDRA, a standardized vocabulary for classifying medical conditions and adverse events. That let the researchers analyze posts as comparable symptom categories rather than isolated anecdotes.

410,198Posts analyzed

Posts mentioning semaglutide or tirzepatide covered May 2019 through June 2025.

43.5%Users reporting a side effect

This share applies to identified Reddit users, not all people taking the medications.

Known symptoms, then possible gaps

Gastrointestinal symptoms were the predominant category among users who described side effects, matching established concerns around these medications. Fatigue was the second-most frequently reported complaint, appearing in 16.7% of the study’s symptom analysis, although the authors said it reached reporting thresholds in relatively few clinical trials they reviewed.

Signals the researchers want examined

• Reproductive symptoms: nearly 4% of users reporting side effects described bleeding between periods, heavy bleeding or irregular menstrual cycles.
• Temperature symptoms: users discussed chills, feeling unusually cold, hot flashes and fever-like symptoms.
• Fatigue: a frequently discussed complaint that was less consistently prominent in the clinical-trial literature reviewed by the authors.

The next test is outside Reddit

The findings are hypothesis-generating, not a safety verdict. Voluntary posts cannot establish how often symptoms occur or whether medication use caused them; symptoms could also reflect weight loss, other health conditions or unrelated factors. The posts also did not consistently provide treatment details needed to test timing or dose relationships.

Reddit users also are not representative of all GLP-1 users; the authors note that they tend to be younger, more likely to be male and disproportionately based in the United States. The team plans to examine other platforms and languages. Whether the same patterns appear in more representative data is the unresolved step before these online signals can guide stronger conclusions.