Penn study finds underreported GLP-1 side effects in 400,000 Reddit posts

September 13, 2026 at 03:46 PM2 min

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A University of Pennsylvania team analyzed more than 400,000 Reddit posts and identified reproductive and body-temperature symptoms reported by users of semaglutide and tirzepatide that may be underrepresented in clinical trials. The study, published in Nature Health, examined over five years of posts from nearly 70,000 users. The findings do not establish causation, but researchers say the spontaneous patient reports reveal signals worth further investigation.

Key Facts

The study analyzed more than 400,000 Reddit posts from nearly 70,000 users over five years.
Nearly 4% of Reddit users in the sample reported menstrual irregularities, a figure that would be higher in a female-only sample.
The study was published in Nature Health and led by Sharath Chandra Guntuku, Lyle Ungar, and Neil Sehgal at Penn Engineering.
Researchers identified two symptom categories deserving further investigation: reproductive symptoms and body-temperature problems such as chills and hot flashes.

Study Methodology

The University of Pennsylvania team analyzed more than 400,000 Reddit posts from nearly 70,000 users over a period of more than five years. The study focused on posts mentioning semaglutide (Ozempic, Wegovy, Rybelsus) and tirzepatide (Mounjaro, Zepbound). Researchers identified two symptom categories that stood out: reproductive symptoms, including menstrual cycle changes, and body-temperature problems such as chills and hot flashes. The findings were published in Nature Health.

Researcher Perspectives

Senior author Sharath Chandra Guntuku noted that well-known side effects like nausea appeared in the data, confirming the method detects real signals. Co-author Lyle Ungar said clinical trials identify the most dangerous side effects but may miss symptoms patients are most concerned about. First author Neil Sehgal stated that nearly 4% of Reddit users in the sample reported menstrual irregularities, which would be even higher in a female-only sample. The researchers emphasized that the study found associations in online discussions, not proof that GLP-1 drugs caused the symptoms.