Retatrutide Side Effects in Clinical Studies
The complete adverse-event record from the four reported Phase 3 trials, and straight answers to the questions the evidence cannot address.
The most frequently reported adverse events were gastrointestinal — nausea, diarrhoea, constipation and vomiting — along with decreased appetite and dysesthesia (altered or unpleasant sensation). Rates rose with dose in most cases. Every figure below is reported alongside its placebo comparator, because a rate without a control group tells you very little.
How to read adverse event data
Three things make the difference between reading these tables well and badly.
- Always look at the placebo column. In TRIUMPH-1, 14.8% of the placebo group reported nausea. People in trials report symptoms whether or not they received the molecule. The signal is the gap, not the raw figure.
- An adverse event is not a proven side effect. It is any unwanted medical occurrence recorded during a trial, regardless of cause. Causality is inferred from the comparison with placebo, not from the event itself.
- Populations differ between trials. TRIUMPH-2 enrolled people with type 2 diabetes; TRIUMPH-3 required established cardiovascular disease. Rates are not interchangeable across trials.
Every reported adverse event, by trial
TRIUMPH-1 — obesity or overweight, without diabetes (80 weeks)
| Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6 | 38.4 | 42.4 | 14.8 |
| Diarrhoea | 25.2 | 34.1 | 32.0 | 13.5 |
| Constipation | 23.8 | 25.9 | 26.1 | 10.9 |
| Vomiting | 10.6 | 22.8 | 25.3 | 4.8 |
| Upper respiratory tract infection | 14.2 | 12.2 | 13.1 | 11.6 |
| Dysesthesia | 5.1 | 12.3 | 12.5 | 0.9 |
| Urinary tract infection | 7.5 | 8.8 | 8.4 | 5.3 |
| Discontinued due to adverse events | 4.1 | 6.9 | 11.3 | 4.9 |
TRIUMPH-2 — obesity or overweight with type 2 diabetes (80 weeks)
| Event | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Diarrhoea | 27.4 | 33.5 | 33.6 | 13.2 |
| Nausea | 13.7 | 20.8 | 28.0 | 8.0 |
| Constipation | 14.0 | 16.2 | 16.8 | 9.4 |
| Decreased appetite | 5.8 | 12.3 | 17.1 | 4.5 |
| Vomiting | 5.5 | 10.2 | 15.7 | 4.2 |
| Dysesthesia | 4.5 | 5.6 | 7.3 | 0.7 |
| Urinary tract infection | 3.8 | 6.3 | 8.0 | 6.6 |
| Discontinued due to adverse events | 3.8 | 11.6 | 7.7 | 4.9 |
TRIUMPH-3 — severe obesity with cardiovascular disease (80 weeks)
| Event | 9 mg | 12 mg | Placebo |
|---|---|---|---|
| Diarrhoea | 30.1 | 24.4 | 8.7 |
| Nausea | 21.7 | 22.4 | 5.8 |
| Constipation | 18.0 | 15.7 | 7.1 |
| Decreased appetite | 13.5 | 14.5 | 3.0 |
| Hyperglycaemia | 3.9 | 3.1 | 13.4 |
| Dysesthesia | 6.4 | 6.4 | 1.3 |
| Urinary tract infection | 6.1 | 7.0 | 5.3 |
| Discontinued due to adverse events | 9.8 | 13.5 | 4.8 |
TRIUMPH-4 — obesity or overweight with knee osteoarthritis (68 weeks)
| Event | 9 mg | 12 mg | Placebo |
|---|---|---|---|
| Nausea | 38.1 | 43.2 | 10.7 |
| Diarrhoea | 34.7 | 33.1 | 13.4 |
| Constipation | 21.8 | 25.0 | 8.7 |
| Vomiting | 20.4 | 20.9 | 0.0 |
| Decreased appetite | 19.0 | 18.2 | 9.4 |
| Dysesthesia | 8.8 | 20.9 | 0.7 |
| Discontinued due to adverse events | 12.2 | 18.2 | 4.0 |
Eli Lilly stated TRIUMPH-4 discontinuation rates “were highly correlated with baseline BMI and included discontinuations for perceived excessive weight loss”. Restricted to baseline BMI ≥35, rates were 8.8% and 12.1% versus 4.8% on placebo.
Questions the evidence does not answer
These are among the most searched questions about retatrutide side effects. In each case the honest answer is that the published evidence does not address it — and saying so is more useful than a confident guess.
Does retatrutide cause cancer?
No cancer finding appears in any primary retatrutide source we located, and cancer does not appear among the reported common adverse events in any of the four Phase 3 trials.
That is an absence of reported evidence, which is not the same as evidence of absence. Cancer risk is normally assessed over periods far longer than the 68 to 104 weeks these trials ran, and through regulatory review of the full data package, which has not yet happened. We cannot tell you there is no risk; we can tell you no such finding has been reported.
Does retatrutide affect the heart?
TRIUMPH-3 reported cardiovascular event analyses in which every confidence interval crossed 1.0, with small event counts, in a trial powered for weight change rather than cardiovascular outcomes.
Those data establish neither benefit nor harm. The trial designed to answer the question is TRIUMPH-Outcomes, with primary completion expected February 2029. See the full analysis →
Does retatrutide cause hair loss?
Hair loss does not appear among the most common adverse events reported in any of the four Phase 3 trials we reviewed. We could not locate primary incidence data, so we cannot give a rate in either direction. If detailed adverse-event tables are published in full, this page will be updated.
Are the side effects different in women?
We could not locate sex-stratified adverse-event data in any primary source for these trials. Reported figures cover the trial population as a whole. No answer is available from the evidence we have.
What happens after stopping?
For the adverse events themselves, Eli Lilly reported that the majority of dysesthesia and urinary tract infection events resolved during treatment. What happens to weight after stopping is a separate question, being studied in TRIUMPH-6 (NCT06859268), which has not reported; primary completion is expected in 2028.
What this page is not
This is a record of what was reported in clinical trials. It is not medical advice, not a complete safety profile, and not a basis for any decision about using any substance. No approved product labelling exists for retatrutide, because there is no approved product. If you are experiencing symptoms, speak to a qualified healthcare professional.