This page summarizes company-reported trial data for an investigational drug. It is not medical advice, and the full safety profile is still being characterized in FDA review.
Retatrutide's side-effect profile in Phase 3 has three parts: the GI effects expected of every incretin-class drug, a new dysesthesia signal that wasn't seen in Phase 2, and an unresolved cardiovascular question from TRIUMPH-3.
The common events: gastrointestinal
Across the TRIUMPH program, the most common adverse events are diarrhea, nausea, constipation, decreased appetite and vomiting — the familiar incretin-class pattern, generally dose-related and concentrated during dose escalation. In TRIUMPH-2, nausea affected 28.0% of participants on 12 mg versus 8.0% on placebo. [1]
The new signal: dysesthesia
Dysesthesia — abnormal skin sensations such as tingling, prickling or heightened sensitivity — was not reported in the Phase 2 trial but appears consistently across Phase 3:
| Trial | Dysesthesia incidence |
|---|---|
| TRIUMPH-1 | 5.1% (4 mg) · 12.3% (9 mg) · 12.5% (12 mg) vs 0.9% placebo [2] |
| TRIUMPH-2 | 4.5–7.3% [4] |
| TRIUMPH-4 | 8.8% (9 mg) · 20.9% (12 mg) [3] |
Lilly says the events were generally mild to moderate and mostly resolved. [4] Because the signal is new, dose-related and consistent across trials, expect it to feature in FDA review and, if the drug is approved, in its labeling.
The open cardiovascular question
TRIUMPH-3 enrolled 1,949 people with severe obesity and established cardiovascular disease. Weight results were strong (21.6% on 9 mg, 22.6% on 12 mg vs 3.2% placebo), with large improvements in triglycerides (−37.0%) and the inflammation marker hsCRP (−51.2%). [1]
The cardiovascular event data, however, is genuinely uncertain: MACE-5 hazard ratio 0.82 (95% CI 0.55–1.22) and MACE-3 hazard ratio 1.12 (0.64–1.96). Both confidence intervals cross 1, so no cardiovascular benefit has been shown — and the point estimates even lean in different directions. [1] TRIUMPH-3 wasn't sized to settle that question; a dedicated outcomes trial would be.
What we don't know yet
- Long-term dysesthesia outcomes beyond "mostly resolved".
- Cardiovascular effects — benefit, neutrality or otherwise.
- Discontinuation rates by cause at the detail level — that arrives with peer-reviewed publications and FDA documents.
- Rare events — at scale, post-marketing surveillance is what finds them, and that only begins after approval.
One more safety point that outranks all of the above in practice: products sold online as "research" retatrutide have none of this safety infrastructure — no verified identity, purity, dose or sterility. The trial data on this page describes the real drug, not those products. See the research-peptide warning.