The NEJM 2023 trial that put retatrutide on the map — 338 participants, 48 weeks, dose-response from 8.7% to 24.2% weight loss. Here's what the data actually shows.
The retatrutide Phase 2 trial was a randomized, double-blind, placebo-controlled trial conducted by Eli Lilly, published in the New England Journal of Medicine in June 2023. It enrolled 338 adults with obesity (BMI ≥30, or ≥27 with weight-related comorbidity) across multiple sites, randomized to once-weekly subcutaneous retatrutide at six dose levels (0.5mg, 1mg, 3mg, 6mg, 8mg, 12mg) or placebo, over 48 weeks.
The trial demonstrated clear dose-dependent weight loss across all active arms. The placebo group lost 2.1% body weight (likely due to lifestyle counseling provided to all participants).
| Dose (weekly) | Mean Weight Loss at 48 wks | vs Placebo |
|---|---|---|
| Placebo | –2.1% | — |
| 0.5mg | –8.7% | –6.6% |
| 1mg | –11.2% | –9.1% |
| 3mg | –17.5% | –15.4% |
| 6mg | –20.9% | –18.8% |
| 8mg | –22.8% | –20.7% |
| 12mg | –24.2% | –22.1% |
One of the most significant findings was that the weight loss curve at 48 weeks had not plateaued in the higher-dose groups. This is clinically meaningful: most GLP-1 trials show a weight loss plateau around 32–40 weeks. Retatrutide's trajectory suggested continued weight loss was occurring at trial end, implying final outcomes with 72+ week treatment (as run in Phase 3) could substantially exceed 24%.
Among participants with prediabetes or type 2 diabetes at baseline, retatrutide produced meaningful HbA1c reductions. Despite the glucagon receptor component (which raises blood sugar in isolation), glycemic outcomes were positive — confirming that GLP-1/GIP co-activation balanced glucagon's hyperglycemic effects at these doses.
Systolic blood pressure decreased by 5–10 mmHg in higher-dose groups. Triglycerides decreased significantly. HDL cholesterol increased modestly. These cardiometabolic improvements are broadly consistent with weight loss effects plus direct GLP-1 vascular effects.
In participants with hepatic steatosis at baseline (assessed by MRI-PDFF), retatrutide produced substantial reductions in liver fat content — greater than what has been observed with GLP-1 monotherapy, attributed to the additional glucagon receptor activation increasing hepatic fat oxidation.
GI adverse events were the most common — consistent with the entire GLP-1 drug class. Nausea was reported by 42–56% of participants in higher-dose groups versus 13% in placebo. Vomiting, diarrhea, and constipation followed similar patterns. The majority of GI events were mild-to-moderate and occurred during dose escalation, resolving with continued treatment at stable doses.
| Adverse Event | Placebo | 3mg | 12mg |
|---|---|---|---|
| Nausea | 13% | 42% | 56% |
| Vomiting | 4% | 17% | 28% |
| Diarrhea | 11% | 20% | 26% |
| Constipation | 9% | 18% | 24% |
| Discontinuation (AE) | 2% | 4% | 16% |
Mean resting heart rate increased by 4–7 bpm in higher-dose groups — a known GLP-1 class effect, consistent with tirzepatide and semaglutide data. No serious cardiac arrhythmia signals were identified.
Serious adverse events occurred in 5–8% of participants across dose groups, with no clear dose-dependent pattern and no clustering around a specific organ system. No pancreatitis cases were reported in this trial — though pancreatitis remains a class concern warranting monitoring.
The 16% discontinuation rate due to adverse events at the 12mg dose — compared to 2% for placebo — is notable. This is higher than tirzepatide's Phase 3 discontinuation rates and suggests the highest retatrutide dose may require more careful dose escalation management. Phase 3 protocols have been designed with this in mind.
The retatrutide Phase 2 results were described as "unprecedented" in obesity pharmacology at the time of publication. Here's the honest framing of what they do and don't tell us:
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