What is retatrutide?

Retatrutide is a single molecule that acts as a triple agonist of the GIP, GLP-1, and glucagon receptors. Its developmental code is LY3437943 and it is being developed by Eli Lilly as a once weekly subcutaneous injection. [1][4]

It belongs to the broader family of incretin based therapies, the same general class as semaglutide and tirzepatide, but it targets one more receptor than either of those. [4]

Published pharmacology describes retatrutide as activating all three receptors together. The proposed result is that glucagon receptor activity raises energy expenditure, while GIP and GLP-1 receptor activity reduce appetite and food intake. The combination is intended to drive weight loss alongside improved blood sugar control. [4]

These are the mechanisms reported by the researchers who developed the molecule, not outcomes guaranteed in any individual.

The findings below are listed newest first.

Phase 3 TRIUMPH-1 (company reported topline, May 2026). Eli Lilly reported that in its pivotal Phase 3 obesity trial the highest dose produced a mean weight reduction of about 28 percent at 80 weeks. These figures come from a company press release and have not yet been peer reviewed or published in full. [5]

Phase 2 obesity trial (Jastreboff and colleagues, New England Journal of Medicine, 2023). In a 48 week randomized, placebo controlled trial of 338 adults with obesity and without type 2 diabetes, mean body weight change ranged up to about 24 percent at the 12 milligram dose, compared with about 2 percent in the placebo group. [1]

Phase 2 type 2 diabetes trial (Rosenstock and colleagues, The Lancet, 2023). In 281 adults with type 2 diabetes, retatrutide reduced HbA1c and body weight across the dose groups over the study period. [2]

Phase 2a liver trial (Sanyal and colleagues, Nature Medicine, 2024). In a substudy of participants with metabolic dysfunction associated steatotic liver disease, most participants on the higher doses reached normal liver fat levels by 48 weeks, while none did on placebo. [3]

No. As of June 2026 retatrutide is investigational and is not approved by the FDA or the EMA for any use. [5][6] In its 2026 Phase 3 announcement, Eli Lilly stated that retatrutide is available only to participants in its clinical trials. [5]

Products sold elsewhere as retatrutide are not approved medicines and their contents, purity, and safety are not verified by any regulator.

In the published trials the most commonly reported side effects were gastrointestinal, including nausea, vomiting, diarrhea, and constipation. These were reported most often during dose escalation, were generally mild to moderate, and were more frequent at higher doses. Some participants stopped treatment because of side effects. [1]

This is a summary of what the trials reported and is not a complete safety profile.

The three differ mainly in how many receptors they target. Semaglutide acts on the GLP-1 receptor. Tirzepatide acts on the GIP and GLP-1 receptors. Retatrutide is described in published trials as a triple agonist that adds the glucagon receptor. [1][4]

Semaglutide and tirzepatide are approved medicines in many regions, whereas retatrutide remains investigational. [5]