A new study suggests that people taking GLP-1 medications for diabetes and obesity are reporting additional side effects online that may not be fully captured in clinical trials.

Researchers from the University of Pennsylvania analyzed more than 400,000 posts on Reddit using artificial intelligence. They identified tens of thousands of users who said they were taking drugs like semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound).

About 44% of these users mentioned at least one side effect.

Many commonly reported symptoms—such as nausea, vomiting, and constipation—matched those already known from clinical trials. However, researchers also observed less-documented complaints, including fatigue, temperature sensitivity (chills or hot flashes), and menstrual changes.

“These are signals, not definitive conclusions—but they come directly from patients and may deserve further attention,” said lead author Neil Sehgal.

New Patterns Emerging Online

Among the less typical symptoms discussed:

* Around 17% of users reported fatigue

* About 4% mentioned menstrual irregularities, such as changes in cycle or bleeding

* Between 1% and 4% described sensitivity to temperature, including chills or hot flashes

Researchers say these findings highlight real-world patient experiences that may not always be fully reflected in controlled trials.

Experts Urge Caution

Not all experts agree that the findings should influence medical conclusions. Yuval Pinto from Johns Hopkins Medicine points out that social media data has limitations.

Because posts are anonymous, researchers cannot verify whether users are actually taking the medications, how long they’ve used them, or whether other conditions or drugs could explain the symptoms.

There’s also no comparison group, unlike in clinical trials where results are measured against a placebo.

Why Clinical Trials Still Matter

Large placebo-controlled studies involving GLP-1 drugs consistently show that the most common side effects are gastrointestinal—such as nausea, diarrhea, and constipation.

Some symptoms mentioned online, like fatigue, do appear in trials but often at similar rates in placebo groups, making it unclear whether the drug is the true cause.

Experts also note that certain changes may be linked to weight loss itself rather than the medication. For example, rapid weight loss can temporarily affect hormones or cause hair shedding.

What This Means for Patients

While the study doesn’t prove that these additional symptoms are caused by GLP-1 drugs, it highlights issues that patients are noticing and discussing.

Researchers hope the findings will encourage further investigation into real-world experiences.

Doctors advise patients to report any new or unusual symptoms. A healthcare provider can assess whether they are related to medication, weight loss, or other factors.