Side Effects of Ozempic and Mounjaro
GLP-1 drugs are thought to act on the hypothalamus, a brain region that helps regulate appetite, hormones, reproduction and body temperature Ark. Agricultural Experiment Station/Flickr

AI analysis of more than 400,000 Reddit posts has flagged clusters of menstrual changes, temperature swings and fatigue reported by people taking blockbuster weight-loss and diabetes drugs such as Ozempic, Wegovy and Mounjaro. These symptoms are not well captured in current drug labelling.

Researchers at the University of Pennsylvania used artificial intelligence to scan posts from nearly 70,000 Reddit users discussing GLP-1 agonists including semaglutide and tirzepatide.

Alongside well-documented gastrointestinal problems, their system repeatedly identified mentions of heavy bleeding, spotting, irregular periods, chills, hot flushes and exhaustion.

The study, published in Nature Health, does not prove these drugs caused the problems. Lead author Neil Sehgal and senior author Sharath Chandra Guntuku, both from Penn, described the results as 'signals' in patient discussion that regulators and doctors may want to investigate further, rather than confirmed side effects.

How AI Turned Slang-Filled Posts Into Safety Signals

The Penn team used large language models, including GPT-4o-mini and GPT-4.1-mini, in what Guntuku called 'computational social listening'.

The approach involved using AI to translate informal, slang-heavy Reddit posts into standardised terms used in the Medical Dictionary for Regulatory Activities, the reference system regulators rely on to classify side effects.

This meant a post reading 'I'm freezing all the time' could be grouped with the clinical term 'feeling unusually cold', allowing researchers to track recurring patterns across hundreds of thousands of posts that would otherwise be difficult to categorise consistently.

Around 44 per cent of Reddit users in the study mentioned at least one side effect when discussing semaglutide or tirzepatide.

Gastrointestinal complaints, including nausea, diarrhoea and constipation, were by far the most common. Researchers said this suggested the AI was capturing genuine patterns rather than random complaints.

Menstrual Changes and Chills Raise New Questions

It was a smaller but more unexpected pattern that drew attention. Nearly 4 per cent of users reporting side effects described reproductive issues, particularly menstrual changes, including heavy bleeding, spotting between periods and irregular cycles.

These symptoms are not well captured in current drug labelling.

Sehgal noted that because Reddit skews male, the proportion of women reporting menstrual changes could be higher in a female-only sample.

Temperature-related symptoms also recurred, with users reporting chills, persistent coldness, hot flushes and fever-like sensations.

Fatigue emerged as the second most commonly mentioned complaint overall, despite being reported too rarely in clinical trials to meet standard reporting thresholds.

Co-author Lyle Ungar said clinical trials 'generally identify the most dangerous side effects' but can miss symptoms that matter most to patients in daily life.

Jena Shaw Tronieri, another co-author from Penn's Center for Weight and Eating Disorders, said the findings did not prove the drugs caused menstrual irregularities or temperature swings, but were enough to justify closer study.

Why Social Media Data Has Limits

Researchers acknowledge significant limitations. Reddit users are not representative of the global population taking GLP-1 drugs, posts are self-reported and unverified, and people experiencing no problems are less likely to post detailed accounts.

The individual claims made in the Reddit posts examined have not been independently verified. The findings therefore cannot establish how frequently the symptoms occur among people taking the drugs or whether the medicines caused them.

GLP-1 receptor agonists are thought to engage the hypothalamus, a brain region involved in regulating hormones and other bodily functions. Researchers say this provides a possible biological explanation worth testing further, rather than evidence that the drugs caused the reported symptoms.

The Penn team plans to expand the research beyond Reddit and beyond English-language posts, to establish whether similar patterns appear across other online communities and more diverse patient groups. They believe rapid AI analysis of social media could eventually serve as an early-warning system for widely used medications.

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