Retatrutide Side Effects
What we know about retatrutide side effects from clinical trials - and the important limitations of this data.
Important Limitations
All data below is from Phase 2 trials only. The full safety profile is NOT established. Phase 3 trials with larger, more diverse populations over longer periods are needed. Long-term effects are completely unknown.
About This Data
Side effect data comes from the Phase 2 TRIUMPH-2 trial published in the New England Journal of Medicine (2023). This trial included approximately 340 participants over 48 weeks. Phase 3 trials will include thousands of participants and provide more reliable safety data.
View study in NEJMCommon Side Effects (Phase 2 Data)
The most frequently reported side effects in Phase 2 trials were gastrointestinal, similar to other GLP-1 medications.
| Side Effect | Frequency | Severity | Notes |
|---|---|---|---|
| Nausea | Up to 25% | Mild to moderate | Most common during dose escalation; often improves over time |
| Diarrhoea | Up to 22% | Mild to moderate | Similar to other GLP-1 medications |
| Vomiting | Up to 16% | Mild to moderate | More common at higher doses |
| Constipation | Up to 14% | Mild | Can occur alongside or instead of diarrhoea |
| Decreased appetite | Common | Expected effect | Part of the mechanism of action for weight loss |
| Dyspepsia | Up to 10% | Mild | Indigestion, stomach discomfort |
Note: Percentages are approximate and varied by dose. Higher doses (12mg) generally had higher side effect rates than lower doses (1mg, 4mg, 8mg). Side effects were dose-dependent and most common during the titration period.
Potential Serious Risks
Based on the GLP-1 class and mechanism of action, these potential risks require monitoring. Phase 3 data will clarify actual risk levels.
Inflammation of the pancreas is a known risk with GLP-1 medications. Cases were rare in Phase 2 but require ongoing monitoring.
Rapid weight loss can increase gallstone risk. This is common across weight loss treatments, not specific to retatrutide.
GLP-1 medications carry warnings about thyroid C-cell tumours based on animal studies. Human relevance is uncertain.
Risk increases when combined with insulin or sulfonylureas. Low risk when used alone based on mechanism.
Cardiovascular outcomes trials are ongoing. Other GLP-1 medications have shown cardiovascular benefits.
Rapid blood sugar improvements can temporarily worsen diabetic retinopathy. Monitoring needed in diabetes patients.
How Side Effects Compare to Other GLP-1 Medications
Similar gastrointestinal profile
The types of side effects (nausea, diarrhoea, vomiting) are similar to semaglutide (Wegovy/Ozempic) and tirzepatide (Mounjaro). This is expected given the shared GLP-1 mechanism.
Glucagon component is new
Retatrutide's glucagon receptor activity is unique among approved obesity medications. Long-term effects of this component are unknown and may introduce different risks.
No direct comparison available
Head-to-head trials comparing retatrutide directly to other GLP-1 medications have not been published. Cross-trial comparisons have significant limitations.
What We Don't Know Yet
The longest trial data is 48 weeks. Effects of taking retatrutide for years are completely unknown.
Phase 2 trials are too small to detect rare side effects that affect 1 in 1,000 or fewer people.
Safety in elderly, those with kidney/liver disease, or other specific groups is not established.
Comprehensive drug interaction studies have not been completed or published.
Why Waiting for Approval Matters
Using unregulated "retatrutide" products means:
- Unknown contents: Products may not contain retatrutide at all, or may contain unknown substances.
- Unknown dosing: Even if the product is genuine, the dose may be wrong, contaminated, or degraded.
- No medical oversight: Side effects won't be properly monitored and interactions won't be checked.
- No recourse: If something goes wrong, there's no accountability or legal protection.
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Medical Disclaimer
This information is for educational purposes only and does not constitute medical advice. Side effect data is from Phase 2 clinical trials only; the full safety profile of retatrutide is not established. Retatrutide is an investigational drug not approved by any regulatory authority. For advice about weight management treatments, consult a qualified healthcare provider.
Data source: Jastreboff et al., NEJM 2023
Last updated: December 2025