Reddit Users Are Reporting GLP-1 Side Effects Not Captured in Clinical Trials

A large-scale analysis of social media posts is offering a fresh look at what people say they’re experiencing in real life while taking a GLP-1 for diabetes or obesity.

While the findings don’t prove the medications caused these symptoms, the authors say the patterns may warrant further study.

“These are signals, not conclusions — but they’re coming directly from patients, unprompted, and that’s worth paying attention to,” says the first author, Neil Sehgal, a doctoral student at the University of Pennsylvania in Philadelphia.

But some experts aren’t so sure the findings are worth further study, given the anonymous nature of Reddit posts.

Study Used AI to Analyze Real-World Patient Reports

To better understand how people experience GLP-1 drugs outside of clinical trials, researchers used AI to analyze Reddit posts from 2019 to 2025.

They identified nearly 70,000 users who said they were taking drugs such as semaglutide (Ozempic, Wegovy) or tirzepatide (Mounjaro, Zepbound). About 44 percent of these users reported at least one side effect.

Many of the most commonly reported symptoms — including nausea, vomiting, and constipation — mirror what participants report in clinical trials.

Some Symptoms Reported Online Aren’t Commonly Seen in Trials

Among the symptoms reported online that aren’t commonly documented in GLP-1 trials:

• About 4 percent of users who reported side effects described menstrual changes, including irregular cycles, heavy bleeding, or spotting between periods.
• About 17 percent of users reported fatigue.
• Temperature-related complaints, including chills, feeling cold, and hot flashes were each reported by 1 to 4 percent of people.

The study is interesting as a computer science paper, but the methods and findings don’t stand up to medical scientific scrutiny, says Yuval Pinto, MD, an obesity and family medicine doctor at Johns Hopkins Medicine in Baltimore.

The data comes from an open, anonymous platform, where researchers can’t verify who is posting or whether users are accurately reporting medication use or symptoms, says Dr. Pinto, who wasn’t involved in the study.

“There also isn’t a way to know if these posts come from people currently taking GLP-1s, how long they’ve taken them, other coexisting conditions, or even other medications they are taking that could be causing these side effects,” he says.

The Findings Should Be Taken With a Grain of Salt

The findings bring attention to symptoms that aren’t consistently reported in GLP-1 clinical trials, or symptoms that failed to meet the threshold for reporting, wrote the authors. In other words, sometimes trial participants do report a certain symptom, but researchers may conclude it’s not significant because people taking a placebo (dummy treatment) have the same experience.

But it’s worth pointing out that there is no placebo group for this Reddit study, says Pinto. While a significant number of people taking a GLP-1 who posted experienced fatigue, it’s not clear how many comparable people not taking a GLP-1 would also report that symptom.

There have been many placebo-controlled trials that have tracked symptoms, and this data has been reliably captured, says Pinto. Across randomized clinical trials of GLP-1 drugs involving thousands of participants, the most common side effects are consistently stomach-related — including nausea, diarrhea, constipation, and vomiting, he says.

“This matches what I see in my practice; people consistently report these GI symptoms, and they rarely report other symptoms,” he says.

When people do experience symptoms outside the norm, it often tends to be unrelated, says Pinto. “People tend to attribute symptoms to the most recent thing in their life, even when there isn’t a connection,” he says.

Some symptoms or changes may be because of the weight loss, not the GLP-1. “For example, some women become more fertile after weight loss and get pregnant — but that’s not a side effect of the GLP-1,” he says.

The same goes for hair loss, he says. “Rapid weight loss can cause temporary hair loss, but it’s not directly caused by the medication,” says Pinto.

What This Means for People Taking GLP-1 Drugs

Researchers hope their findings will encourage doctors 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.

Pinto agrees that people should feel empowered to talk to their healthcare providers about any symptoms they are experiencing.

“Your doctor is in the best position to know important factors that could impact symptoms, including your health history, your GLP-1 dosage, how long you’ve been taking it, and other medications you are taking,” he says.