// Contents
13,589 Reddit users say they are currently injecting themselves with retatrutide. It is an experimental Eli Lilly obesity drug that no regulator has approved: Lilly plans to file with the FDA in early 2027. University of Pennsylvania researchers ran their posts through a language model and listed the complaints. The top entry was increased appetite. For a drug built to switch hunger off.
The paper appeared in JAMA Network Open on 14 October 2026 . It is not a clinical trial: the authors studied what people say online and call their results hypotheses. Still, they show how a market works for a medicine nobody officially sells.
A triple hit that people heard about too early
Retatrutide mimics three hormones at once. Two of them, GLP-1 and GIP, are released by the gut after a meal: they help the body handle sugar, and GLP-1 also tells the brain it is time to stop eating. The third, glucagon, makes the body burn its reserves. Semaglutide, the active ingredient in Ozempic, hits one target and tirzepatide two. Three should mean less hunger and faster weight loss. In the phase 2 trial published in NEJM in 2023 , people on the highest dose lost an average of 24.2% of their body weight in 48 weeks.
In July 2026 Lilly reported two phase 3 trials . TRIUMPH-3 enrolled people with severe obesity and heart disease, and over 80 weeks they lost up to 22.6% of their weight. TRIUMPH-2 tested the drug in people with excess weight and type 2 diabetes. Such numbers went viral long before approval. Not everyone waited.
Penn computer science doctoral student Neil Sehgal and senior author Sharath Chandra Guntuku collected 148,640 Reddit posts and comments about retatrutide, peptides and weight loss. Retatrutide is itself a peptide, a short chain of amino acids. A whole class of such substances is sold online as “research peptides”.
A language model picked out people describing their own injections and translated their symptoms into MedDRA, the dictionary regulators use to sort side effects. Weight loss and reduced appetite counted as the drug’s expected effects, not complaints. That left 7,823 people with at least one complaint.
How the model read the posts
Posts come from 27 communities and run from May 2021 to December 2025. A small model, gpt-5.4-nano, decided whether people wrote about themselves, extracted dose, sex and age, and mapped symptoms to MedDRA. Current retatrutide use was reported by 13,589 people across 45,592 posts and comments. A hand check of 100 posts showed high accuracy. After excluding expected effects, 7,823 users remained.
Hunger first, nausea fourth
Increased appetite was mentioned by 1,336 people, or 17.1% of those with at least one complaint. Another 7.3% complained of food cravings.
Next comes a pair that sits oddly on one list. Fatigue is second, at 15.2%, and a surge of energy is third, at 12.4%.
Nausea, the classic trouble with this class of drugs, came only fourth at 11.6%. The Atlanta Journal-Constitution described one case. Camila Zicarelli, 27, injected retatrutide from a Georgia clinic for six months and estimates she spent about $1,200. She felt nauseous until she lowered her dose. Insomnia and a racing heart close the list.
Run on semaglutide and tirzepatide, the same method put nausea, vomiting and digestion on top. Retatrutide posts lean towards appetite, sleep, muscles and heartbeat. The comparison is rough, with no statistics.
// What the trials saw and what Reddit says
Trials
In TRIUMPH-2, diarrhoea affected 27–34% of participants on the drug against 13% on placebo, and nausea 14–28%. In phase 2, heart rate rose with dose, peaked at week 24 and then declined. Doctors gave the drug, so doses and contents were known.
Increased appetite comes first, at 17.1%, nausea fourth, at 11.6%. These shares are of people with a complaint, while trial figures are of all participants, so compare the order, not the numbers. Nobody can check what was in the vial or what else people injected.
The heart rate is no news: trials saw it too. Appetite is the reverse. In TRIUMPH-2 it dropped so sharply that reduced appetite was logged as a side effect in 6–17% of participants. On Reddit reduced appetite was not counted at all, as an expected effect. So the puzzle is why hunger tops the complaint list in the first place. Penn’s Jena Shaw Tronieri, who studies weight and eating disorders, puts it carefully : retatrutide works differently from existing GLP-1 drugs, and what, if anything, the differences mean needs more research.
What gets sold under that name
“I will risk my career on retatrutide,” Kent Cohen, a former emergency physician who co-owns the Balanced Bodies clinic chain in Georgia, told the Atlanta Journal-Constitution. A course there starts at $350 a month. On 15 October 2026 the paper counted 17 Georgia medical facilities offering the drug, nearly half run or directed by physicians. He insists this is legal. Lilly says anyone purporting to sell the drug to consumers, is breaking the law.
There is a more mundane explanation for the hunger, and the authors spell it out: nobody knows what these people inject. Online, it is sold labelled “for research use only, not for human consumption”. The advocacy group Public Citizen reported in June 2026 that the FDA had sent such sellers 14 warning letters since 2024, yet by May eight still sold retatrutide. Hundreds of affiliate influencers send buyers their way.
How well does gray-market retatrutide work? Analytics firm nference searched health records and found 378 people who got retatrutide outside trials, mostly from online vendors and compounding pharmacies. According to its preprint , they lost 7.2% of their weight over six to twelve months, against 15.5% for trial participants. It is not yet peer reviewed. If a vial holds less than its label says, or something else entirely, the hunger looks less mysterious. That is unproven, one of the explanations the authors list.
Why scientists read other people’s complaints
FDA data cited by the Atlanta Journal-Constitution show more than 70 adverse event reports involving retatrutide since 2024, including four deaths in 2026. The reports are unverified and prove no causation. Gray-market buyers have no clinical data, only their own accounts.
Reddit already has one hit as a source. In April 2026 the same group analysed in Nature Health more than 400,000 posts from nearly 70,000 users of semaglutide and tirzepatide. Nearly 4% of them mentioned menstrual irregularities. Later, another team checked the FDA database and found a disproportionate number of the same complaints there.
So the authors address doctors: ask patients without judgement about unapproved peptides, warn that contents are unknown, and report reactions to MedWatch, the FDA’s side-effect reporting system. Co-author Lyle Ungar draws the line plainly: the researchers cannot say that retatrutide is causing these symptoms.
If the hunger in these posts proves as real a signal as the menstrual complaints, it may say more about what is in the vials than about the drug itself. For now, only those 13,589 users know what it is like to inject something labelled “not for human consumption”, and even they cannot say what was in the vial.
