Researchers at the University of Pennsylvania used language models to analyse over 400,000 Reddit posts about semaglutide and tirzepatide. Five years of entries from roughly 70,000 users surfaced complaints that rarely reach official tallies — from menstrual irregularities to hot flashes. The work appeared in Nature Health.
Key takeaways
- Over 400,000 Reddit posts from roughly 70,000 users, five years of data.
- A language model translated colloquial descriptions into MedDRA medical terminology.
- Nearly 4 percent of reports concerned menstrual irregularities.
- Fatigue was the second most common complaint, gastrointestinal problems the first.
- Published in Nature Health 2026, volume 1, issue 8, page 806.
Translating from internet into medical
The problem with forum data is always the same: people do not write "moderate-intensity nausea", they write "second day of throwing up at everything". The Pennsylvania team used a language model as a translator — mapping informal descriptions onto MedDRA?MedDRA: The international medical dictionary used when reporting adverse drug reactions. Regulators require every symptom to be expressed as one of its fixed terms., the vocabulary regulators use when reporting adverse events. Only on that normalised data could frequencies be counted.
Symptoms that never reach the statistics
Gastrointestinal complaints stayed at the top, which is no surprise for GLP-1?GLP-1: A class of drugs mimicking the hormone that regulates appetite and blood sugar. Semaglutide and tirzepatide belong to it, used in type 2 diabetes and obesity treatment. drugs. What came next is more interesting. The authors point to the hypothalamus, which regulates hormones, reproduction and body temperature at once — precisely the three areas the new signals come from.
| Symptom | How often | Status in the study |
|---|---|---|
| Gastrointestinal complaints | most common | consistent with the known GLP-1 profile |
| Fatigue | second most common complaint | rarely reported through official channels |
| Menstrual irregularities | nearly 4% of reports | flagged as a direction for clinical study |
| Chills, hot flashes, feeling cold | recurring | authors' hypothesis: the hypothalamus |
A forum versus the official reporting registry
Classic adverse-event reporting depends on a patient picking up the phone or writing to a doctor. Forum posts are written for a different reason — someone wants to ask whether anyone else has this. That is why they catch symptoms considered too trivial or too embarrassing to report formally.
Why it matters
This is not news about a drug but about a method. Here the language model stops being a text generator and becomes a data-normalisation tool — turning millions of unstructured statements into something countable. If the approach sticks, drug-safety surveillance gains an extra, faster signal channel. Provided nobody mistakes a signal for proof.
What's next?
- The authors flag menstrual irregularities and thermoregulation symptoms as directions requiring clinical rather than observational study.
- The method transfers to other drug classes — the limiting factor is the quality of mapping colloquial language onto MedDRA.
