AI Scans 150,000 Reddit Posts to Flag Side Effects of Gray-Market GLP-1 Drug Retatrutide

A drug that has never been approved for human use is already circulating widely enough that researchers can study its side effects from the outside. Retatrutide, an experimental weight-loss medication developed by Eli Lilly, remains in Phase 3 clinical trials, the final stage of testing before potential approval by the U.S. Food and Drug Administration. Yet online forums are filled with people describing their experiences with gray-market versions of the compound, formulations that are not intended for human consumption and whose contents and purity cannot be verified. Now a team at the University of Pennsylvania has turned artificial intelligence loose on those conversations, producing the first systematic look at what users of unapproved retatrutide say is happening to their bodies.

In a study published in JAMA Network Open, researchers analyzed nearly 150,000 Reddit posts and comments from roughly 40,000 users, using large language models to identify approximately 14,000 people who described personally taking an unapproved version of the drug. The AI tools then extracted symptoms those users attributed to retatrutide and mapped their descriptions onto standardized medical terminology, ultimately narrowing the sample to 7,823 users who reported at least one classifiable symptom beyond the expected effects of weight loss and appetite suppression. The result is an unprecedented window into a population that conventional drug-safety monitoring simply cannot reach.

“Our goal is to identify hypotheses in online conversations that we could test. AI helps us find recurring patterns in people’s self-reports, including experiences that may be missed by conventional drug-safety monitoring,” says Sharath Chandra Guntuku, Research Associate Professor in Computer and Information Science, Director of Penn’s Computational Social Listening Lab and senior author of the new paper. The approach treats social media not as evidence in itself but as a signal detector, a way of surfacing patterns that clinical trials and regulatory reporting systems may never capture.

The most striking finding was what the Reddit users reported most often. Among those who shared classifiable potential symptoms, the most frequently mentioned was increased appetite, an outcome that stands in sharp contrast to retatrutide’s Phase 2 clinical trials, where gastrointestinal complaints such as nausea were identified as the most common side effects. For a drug whose demonstrated effect is powerful weight loss, self-reports of heightened hunger among gray-market users were unexpected, and the discrepancy immediately raises questions about what distinguishes this population from trial participants.

The researchers are careful to emphasize that the differences do not establish that retatrutide causes the reported symptoms, nor that the experiences of Reddit users mirror those of clinical trial participants. “We can’t say that retatrutide is causing these symptoms, or even that Reddit users are actually taking genuine retatrutide, since the drug is not legally available, and gray market formulations vary,” says Lyle Ungar, Professor in Computer and Information Science and a co-author of the study. The gray market offers no quality control, no verified dosing and no assurance that the vials people inject contain what the labels claim.

Retatrutide belongs to a new generation of obesity medications, and its pharmacology is precisely why the Penn team suspected its side-effect profile might look different. Semaglutide, the active ingredient in Ozempic and Wegovy, activates a single hormone receptor involved in regulating appetite and blood sugar. Tirzepatide, sold as Mounjaro and Zepbound, activates two. Retatrutide activates three, a triple-agonist mechanism that gives the drug its potency and, potentially, a distinct pattern of effects on the body. “Retatrutide works differently from existing GLP-1 drugs, so it’s possible that its effects on the body are different, too,” says Jena Shaw Tronieri, Senior Research Investigator at Penn’s Center for Weight and Eating Disorders and a co-author of the study.

But Tronieri also points to a second explanation that may be just as important: the people themselves. “But the people discussing it on Reddit also may be different,” she notes. “Users willing to obtain an unapproved medication on the gray market likely differ from other clinical populations. Some may be taking multiple experimental peptides, and we can’t verify exactly what they’re taking. We need more research to understand what, if anything, these differences in self-reported symptoms mean.” Compared with the team’s earlier analysis of semaglutide and tirzepatide, the retatrutide posts featured proportionally more reports of appetite-related symptoms, sleep disturbances, increased heart rate and muscle-related changes, and fewer reports of nausea and other gastrointestinal symptoms.

The new study builds directly on that earlier work, in which the same Penn team used large language models to analyze more than 400,000 Reddit posts about semaglutide and tirzepatide, identifying potential side effects, including menstrual irregularities, that had not been fully captured in clinical trials or regulatory documents. That finding did not remain confined to social media. After the researchers surfaced reports of menstrual changes among GLP-1 users, another research group pursued the same question using the FDA’s adverse-event database, and their subsequent study, published in Obstetrics & Gynecology, also identified disproportionate reports of certain menstrual changes, lending additional weight to the signal.

That sequence is exactly the model the Penn researchers hope this retatrutide analysis will follow. “This is the first glimpse into the experiences of a population that is otherwise outside conventional drug safety monitoring because they are taking unapproved versions of a drug that has yet to finish clinical trials,” says Neil Sehgal, the study’s first author and a doctoral student in Computer and Information Science. “Other researchers can take what we find on Reddit and look for the same patterns in other datasets, using entirely different methods. Whether those signals hold up or not, the goal is to build a better understanding of what people are actually experiencing.”

The scale of the analysis is what makes it feasible at all. “A researcher might be able to examine a few thousand Reddit posts by hand, but looking at nearly 150,000 would be an enormous undertaking,” says Sehgal. “AI makes it possible to analyze these conversations at scale, identifying patterns in what people are sharing that would otherwise be difficult to recognize.” The study was conducted at the University of Pennsylvania School of Engineering and Applied Science and the Perelman School of Medicine, with additional co-authorship from Benjamin Rader of Boston Children’s Hospital and funding support in part from Penn’s Medical Communication Research Institute. As gray-market demand for unapproved obesity drugs continues to grow faster than the regulatory system can respond, the study suggests that the conversations people are already having online may become an essential early-warning system, provided the signals they contain are pursued with the rigor they ultimately require.

Subject of Research: AI analysis of Reddit posts to identify self-reported side effects of unapproved gray-market retatrutide, a triple-agonist GLP-1 weight-loss drug

Article Title: Penn engineers use AI, Reddit to identify potential side effects of unapproved new GLP-1

Article References: Penn engineers use AI, Reddit to identify potential side effects of unapproved new GLP-1. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: retatrutide, GLP-1 drugs, gray-market medications, pharmacovigilance, artificial intelligence, large language models, Reddit, drug safety, obesity treatment, social media analysis, adverse effects, University of Pennsylvania