A peer-reviewed Nature Health study analyzed 410,198 Reddit posts from 67,008 self-reported GLP-1 users. Three categories of symptoms — menstrual irregularities, fatigue, and temperature dysregulation — appeared at rates that current drug labeling underreports. Findings are not causal, but the signal is strong enough to warrant follow-up research.
Published April 2026 in Nature Health (DOI: 10.1038/s44360-026-00108-y), the study was authored by Neil K.R. Sehgal, Jena Shaw Tronieri, Lyle Ungar, and Sharath Chandra Guntuku at the University of Pennsylvania School of Engineering and Applied Science.
Dataset
Posts were pulled from public Reddit APIs (Pushshift, arctic_shift) covering May 2019 through June 2025. The research team used LLMs (GPT and Gemini) to map unstructured user text to MedDRA — the standardized medical terminology used in regulatory adverse-event reporting. The method's validation step: reported rates for known GI side effects (nausea, vomiting, constipation, diarrhea) closely matched clinical trial data, confirming the AI was extracting real signal rather than noise.
Confirmed Against Clinical Trials
GI symptoms matched the known safety profile: nausea (36.9%), fatigue (16.7%), vomiting (16.3%), constipation (15.3%), diarrhea (12.6%). This alignment lends credibility to the novel findings below.
The Three Novel Signals
Users reported irregular cycles, heavier or lighter bleeding, and spotting. Because Reddit skews male, the actual rate in female GLP-1 users is likely higher. Co-author Sehgal flagged this as "a signal worth investigating."
Fatigue appears inconsistently on current labeling because placebo groups often report it at similar rates, pushing it below significance thresholds. Reddit data shows roughly 1 in 6 users discussing it unprompted.
Chills, persistent cold, and hot flashes — not previously tracked as GLP-1 side effects. Possible mechanisms include metabolic shifts, loss of subcutaneous fat (thermal insulation), or direct thermoregulatory drug effects.
Limitations
The authors are explicit that findings are not causal. Reddit users can't be verified, there's no placebo comparison group, and rapid weight loss itself — independent of the drug — can cause many of these symptoms. Dr. Yuval Pinto of Johns Hopkins raised these caveats in Everyday Health's coverage, noting that the population (younger, more male, US-based) isn't representative of all GLP-1 users globally.
Sample demographics (per the study): Reddit users skew younger, disproportionately male, and disproportionately US-based. Authors explicitly call this a limitation and have proposed extending the methodology to non-English platforms and non-Reddit forums.
Methodology Implications
The authors frame their approach as "computational social listening" — a pharmacovigilance supplement (not replacement) that can catch emerging safety signals faster than FAERS reporting or trial-based surveillance. For loosely regulated market segments (compounded peptides, unapproved GLP-1 analogs), this method may become essential to early safety detection.
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- Sehgal, N.K.R., Tronieri, J.S., Ungar, L., Guntuku, S.C. "Self-reported side effects of semaglutide and tirzepatide in online communities." Nature Health, April 2026. DOI: 10.1038/s44360-026-00108-y
- Sehgal et al. Preprint: arXiv:2603.12341 (March 2026).
- Penn Engineering. "Penn Researchers Use AI to Surface Unreported GLP-1 Side Effects in Reddit Posts." seas.upenn.edu, April 2026.
- Upham, B. "Reddit Users Are Reporting GLP-1 Side Effects Not Captured in Clinical Trials." Everyday Health, April 10, 2026.
- EurekAlert! (AAAS). "Penn researchers use AI to surface unreported GLP-1 side effects in Reddit posts." Press release, April 2026.