Popular weight-loss medications linked to hidden side effects, study finds

In a sweeping analysis of more than 400,000 Reddit posts, researchers have revealed some little-known GLP-1 side effects.

GLP-1 receptor agonists — such as semaglutide (Ozempic and Wegovy), and tirzepatide (Mounjaro and Zepbound) — have been most commonly associated with gastrointestinal side effects, such as nausea, vomiting, diarrhea and constipation.

A new study published in Nature Health, however, uncovered some overlooked effects.

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University of Pennsylvania researchers used artificial intelligence to analyze more than five years of Reddit posts from more than 67,000 people taking the popular drugs for diabetes or weight loss.

While clinical trials are still the "gold standard," the researchers noted that Reddit community feedback reflects a different population.

"People often use medications differently than they're prescribed, so it's also important to look at real-world usage, which can diverge from usage in a clinical trial," lead researcher Neil Sehgal, a PhD student at the University of Pennsylvania, told Fox News Digital. "So there are many possible reasons we're seeing signals that the trials may have missed."

Nearly half of the users reported one or more side effects. The most common were nausea, vomiting and constipation, which aligned with what clinical trials found, according to Sehgal.

"We did notice a few side effects that have not previously been reported for these drugs," he told Fox News Digital. 

"For example, about 4% of users who described side effects reported menstrual irregularities. Other Redditors described unusual temperature-related symptoms, like chills or hot flashes."

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Nearly 13% of users also experienced psychiatric symptoms, such as anxiety, depression and insomnia. More than 5% also complained of abdominal pain, acid reflux, headache and dizziness.

"Fatigue was also the second most commonly reported symptom overall, but has met relatively few reporting thresholds in existing trials," Sehgal noted. "This gap between what patients are self-reporting online and what gets captured in trials is really what motivated this whole line of work."

Dr. Sue Decotiis, a New York City-based board-certified weight-loss physician, noted that many of the reported symptoms, such as disorientation and fatigue, are most likely due to dehydration and hypoglycemia (low blood sugar).

"Patients should be carefully monitored using a structured protocol that ensures proper nutrition and adequate hydration, ideally under the direct supervision of a physician experienced in metabolism and weight loss," Decotiis, who was not involved in the study, told Fox News Digital. 

"Additionally, body composition analysis can help identify issues such as muscle loss, excessive water loss or insufficient fat loss."

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A significant concern, according to the doctor, is that many individuals are accessing these medications through online platforms or without receiving appropriate medical care. 

"In my experience treating thousands of patients with various GLP-1 medications, complications are rare and typically occur only when patients are noncompliant," she added.

As the data came from Reddit users, who tend to be younger, primarily male and mostly based in the U.S., it may not represent everyone taking these medications, the researchers noted.

"And even within Reddit, the people who post about their side effects are probably not typical of everyone on the medication," Sehgal said. "If you had a good experience, you're less likely to be writing about it online. So we're almost certainly capturing a skewed slice of the full picture."

The researchers also noted that the study can’t prove the drug caused the reported symptoms.

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"To be clear, we can’t say for certain whether these drugs are causing menstrual irregularities," Sehgal said. "Patients on Reddit aren't going to self-report every symptom they have, and they may also report things that aren't actually linked to the medications. So it's important to treat this as hypothesis-generating signals and do more research."

The study also didn’t include GLP-1 dosage, duration of the medication and symptoms, or other health conditions the users experienced. There is also the chance that the AI tools misunderstood meanings or context, the researchers noted.

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The results must be confirmed with more rigorous research, Sehgal said. "That's how we'll get real answers about prevalence and causality, which social media data alone can't provide." 

"These are signals, not conclusions – but I do think it's always worth talking to your doctor about anything unexpected you're experiencing while on a new medication, even if you're not sure if it's related," he advised. "So if something feels off, say something."