By Lew Kizer — 2026-10-24 — Health & Nutrition
The short answer
A University of Pennsylvania study published in JAMA Network Open in October 2026 used AI to analyze about 150,000 Reddit posts and comments from 40,000 users about retatrutide, an investigational drug still in Phase 3 trials. About 14,000 users said they had taken unapproved retatrutide; 7,823 reported at least one classifiable symptom, most often increased appetite. The study cannot show the drug caused the symptoms.
Key facts
- Published in JAMA Network Open, 2026; 9(10): e2638929.
- About 150,000 posts and comments from about 40,000 Reddit users.
- About 14,000 users said they personally took gray-market retatrutide; 7,823 reported a classifiable symptom.
- Most common: increased appetite, the opposite of the drug's intended effect.
- More mentions of sleep problems, faster heart rate and muscle symptoms than in earlier semaglutide and tirzepatide posts.
- Retatrutide is not FDA-approved; it remains in Phase 3 trials.
KINGSPORT, Tenn., Oct. 24, 2026 — Retatrutide is not approved, but thousands of people are already taking something sold under its name. Researchers at the University of Pennsylvania used AI to read what they say about it.
This article reports research news and is not medical advice. Talk with your clinician before changing your diet, supplements or medicines.
How the study worked
The team analyzed about 150,000 Reddit posts and comments from about 40,000 users. AI tools pulled out symptom descriptions and mapped them to medical terms, leaving out expected effects such as weight loss. About 14,000 users said they had personally taken unapproved retatrutide, and 7,823 reported at least one classifiable symptom.
| Compared with earlier semaglutide and tirzepatide posts | Retatrutide posts mentioned |
|---|---|
| Appetite changes | More often |
| Sleep disturbances | More often |
| Increased heart rate | More often |
| Muscle-related symptoms | More often |
| Nausea and digestive complaints | Less often |
What the researchers warn
“We can't say that retatrutide is causing these symptoms” — Lyle Ungar, Professor, University of Pennsylvania
Jena Shaw Tronieri of Penn's Center for Weight and Eating Disorders added: “Some may be taking multiple experimental peptides, and we can't verify exactly what they're taking.” Gray-market products may differ in ingredients, purity and dose from what was tested in trials.
Our retatrutide food guide explains what the trials have shown so far.
Safer ground
“When you're on a GLP-1 medication, what you eat matters more, not less. You need high-protein, portion-controlled, nutrient-dense food — and you need to know it's safe. That's exactly what we do.” — Lew Kizer, Founder, SmashMeals
Commentary, not medical advice
The SmashMeals perspective
We cook for a lot of people on GLP-1 medicines, and we hear about the shortcuts. This study is a reminder that a vial from the internet is not the drug that was tested in a trial. If you are using these medicines, use them through a prescriber who can watch for problems, and put your energy into the part you control: eating enough protein and real food on a smaller appetite.
Frequently asked questions
Is retatrutide FDA-approved?
No. Retatrutide is an investigational drug in Phase 3 trials. Products sold online are unapproved.
What side effects did gray-market retatrutide users report?
In the Penn analysis of Reddit posts, increased appetite was the most common classifiable symptom. Users also mentioned sleep problems, faster heart rate and muscle symptoms more often than semaglutide and tirzepatide users had in earlier posts.
Does this prove retatrutide causes those symptoms?
No. Researchers could not verify what users took, many may use several peptides, and Reddit users differ from trial participants.
Sources and credits
Follow the original sources for context and verification. A reference is not an endorsement of SmashMeals.
- People are taking an unapproved weight-loss drug. AI found something surprising (opens in a new tab)
ScienceDaily (University of Pennsylvania)
Why it matters: Summary of methods, findings and researcher cautions.
- JAMA Network Open study (DOI 10.1001/jamanetworkopen.2026.38929) (opens in a new tab)
JAMA Network Open
Why it matters: The peer-reviewed paper.