AI Analysis Reveals Hidden Side Effects Of Popular Weight Loss Drug

An artificial intelligence (AI) analysis of over 400,000 Reddit posts found that people taking GLP-1 medications frequently report side effects not fully captured in clinical trials or drug labels.

In September 2025, the WHO added Glucagon-Like Peptide-1 (GLP-1) therapies to its Essential Medicines List specifically as therapies for managing obesity and type 2 diabetes in high-risk groups.

The World Health Organization (WHO) then released its first global guideline recommending GLP-1 receptor agonists (such as semaglutide, liraglutide, and tirzepatide) for treating obesity on December 1, 2025.

These guidelines, published in JAMA, recommend the drugs for adults with a BMI of 30 or higher.

Over time, there is a growing demand for GLP-1–based therapies, with research suggesting roughly 1 in 8 U.S. adults reporting having ever used GLP-1 medication, with 6% currently using such drugs.

Although many of the known side effects are mild to moderate in severity and generally resolve shortly such as nausea, vomiting, diarrhea and constipation, a new study published in Nature Health used AI to analyze social media posts and uncovered patient-reported side effects linked to these medications.

The analysis identified two main symptom categories that may warrant further investigation. These included reproductive symptoms, including irregular menstrual cycles and unexpected bleeding, and temperature-related issues, such as chills, hot flashes, and feeling unusually cold.

“Some of the side effects we found, like nausea, are well known, and that shows that the method is picking up a real signal,” says Sharath Chandra Guntuku, Research Associate Professor in Computer and Information Science (CIS) at Penn Engineering and the study’s senior author. “The underreported symptoms are leads that came from patients themselves, unprompted, and clinicians could potentially pay attention to them.”

The researchers caution that their findings are not causal.

"We can't say that GLP-1s are actually causing these symptoms," notes Neil Sehgal, the study's first author and a doctoral student in CIS advised by Guntuku and Ungar. "But nearly 4% of the Reddit users in our sample reported menstrual irregularities, which would be even higher in a female-only sample. We think that's a signal worth investigating.”

“These drugs are thought to work by engaging part of the brain called the hypothalamus, which helps regulate a wide variety of hormones," says Jena Shaw Tronieri, Senior Research Investigator at Penn's Center for Weight and Eating Disorders and a co-author of the study.

"That doesn't mean the medications are necessarily causing these symptoms, but it could suggest that reports of menstrual changes and body temperature fluctuations are worth studying more systematically.”

In addition, fatigue ranked as the second most common complaint among Reddit users.

In the near term, the researchers hope their findings will encourage clinicians and researchers to take a closer look at the side effects patients are discussing online. "They're clearly on patients' minds, and that's worth paying attention to," says Sehgal.

The team also hopes to expand the work beyond Reddit and beyond English-language communities to test whether the same patterns appear across different platforms and populations.

Ultimately, the researchers believe this kind of rapid, AI-assisted social media analysis could become a useful way to spot early warning signs around emerging drugs and wellness trends.

"The whole point of this kind of approach is that it can move quickly, and that's exactly when i

t's most valuable," says Guntuku.