Study Flags Underreported Side Effects in Popular Weight Loss Drugs

AI analysis of hundreds of thousands of online posts identifies reproductive and temperature-related symptoms not widely documented in clinical trials.

Haika Mrema

Published: 4/17/2026, 4:20:41 PM EDT

Study Flags Underreported Side Effects in Popular Weight Loss Drugs — An obesity doctor and consultant showing various GLP-1 self-injectable devices at a clinic in Mumbai on March 17, 2026. (Indranil Mukherjee/AFP via Getty Images)

A new study has identified a range of lesser-known side effects linked to widely used weight loss and diabetes medications, raising questions about how fully current safety data reflects patient experiences.

“Some of the side effects we found, like nausea, are well known, and that shows that the method is picking up a real signal,” said Sharath Chandra Guntuku, senior author of the study, in comments published by Medical Xpress. “The underreported symptoms are leads that came from patients themselves, unprompted, and clinicians could potentially pay attention to them.”

The findings come from a research team at the University of Pennsylvania, which analyzed more than 400,000 Reddit posts spanning over five years. The study, published in Nature Health, examined discussions from nearly 70,000 users who reported taking GLP-1 drugs such as semaglutide and tirzepatide, medications that have surged in popularity for weight loss.

Using artificial intelligence to process the large dataset, researchers found that 43.5 percent of users reported at least one side effect. As expected, gastrointestinal symptoms were the most common, including nausea, fatigue, vomiting, constipation, and diarrhea, according to the study.

However, the analysis also surfaced less-documented concerns. Among them were reproductive symptoms, such as irregular menstrual cycles, heavy bleeding, and intermenstrual bleeding, as well as temperature-related complaints, including chills, hot flashes, and fever-like sensations.

“Clinical trials generally identify the most dangerous side effects of drugs,” co-author Lyle Ungar said in the Medical Xpress report. “But they can fail to find what symptoms patients are most concerned about.”

Researchers emphasized that the findings do not establish a causal link between the medications and the reported symptoms. “We can’t say that GLP-1s are actually causing these symptoms,” said lead author Neil Sehgal, noting that the data reflects self-reported experiences rather than controlled clinical outcomes.

Still, the study suggests that patient discussions online may reveal patterns not fully captured in traditional trials. Nearly 4 percent of users reporting side effects described reproductive issues, an observation researchers said warrants further investigation.

The study also highlights the growing role of social media in identifying potential health signals. Researchers described online forums as a form of “computational social listening,” where large-scale patient conversations can provide early insights into real-world drug experiences.

According to the Mayo Clinic, the most commonly recognized side effects of GLP-1 medications remain gastrointestinal, including nausea, vomiting, diarrhea, and headaches. These effects are well documented in clinical trials and current prescribing information.

Researchers say their findings are not a replacement for clinical studies but could serve as a complementary tool, helping clinicians and regulators identify emerging concerns more quickly as the use of these medications continues to expand.

"The whole point of this kind of approach is that it can move quickly, and that's exactly when it's most valuable," Sharath Chandra Guntuku, a senior author of the study, said of utilizing social media sites, including TikTok and Reddit.