Quick answer: in the published Phase 2 trial of retatrutide (GLP-3 RT), the most common adverse events were gastrointestinal: nausea, diarrhea, vomiting, and constipation. They were dose-related, mostly mild to moderate, and clustered during dose escalation. A dose-dependent increase in heart rate was also reported, peaking early and declining over the study.
What the published data covers
Retatrutide is a single-molecule agonist of the GIP, GLP-1, and glucagon receptors. The main source for its adverse-event profile is a 48-week, randomized, placebo-controlled Phase 2 trial in adults with obesity published in the New England Journal of Medicine in 2023, along with a parallel Phase 2 trial in type 2 diabetes published in The Lancet. This article summarizes what those papers reported. It is a literature review for research reference, not clinical guidance.
Gastrointestinal events
Across dose groups, the most frequently reported adverse events were nausea, diarrhea, vomiting, and constipation. The authors described them as mostly mild to moderate in severity, dose-related, and occurring primarily during the dose-escalation period. The trial used a gradual escalation schedule, and the papers note that slower escalation was associated with fewer early gastrointestinal events. Discontinuation because of adverse events was more common at the higher doses.
Cardiovascular observations
A dose-dependent increase in heart rate was reported. In the obesity trial, the increase peaked around week 24 and declined thereafter, a pattern the authors described as not monotonic. Blood pressure was reported to decrease alongside weight reduction. These are trial observations, and the papers call for longer studies to characterize them.
Other reported events
- Dysesthesia (skin sensation changes) was reported at higher doses and was generally mild.
- Cardiac arrhythmia events were reported in a small number of participants across groups.
- No new safety signals were identified beyond those known for the GLP-1 receptor agonist class, according to the authors.
Reading this data as a researcher
Phase 2 trials are designed to find a dose range and a preliminary safety picture, not to characterize rare events. The cohorts were a few hundred participants per trial. Larger Phase 3 programs are ongoing and will define the profile more completely. When citing adverse-event data, note the dose group, the escalation schedule, and the duration, since all three shaped the numbers reported.
Sources
- Jastreboff AM et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial. New England Journal of Medicine, 2023.
- Rosenstock J et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes: a randomised, double-blind, placebo and active-controlled, parallel-group, phase 2 trial. The Lancet, 2023.
- Coskun T et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Cell Metabolism, 2022.
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