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Retatrutide: Research Summary

Published: 2026-08-03 · Last updated: 2026-08-03

Mechanism

Retatrutide (LY3437943) is a single-molecule triple agonist at the glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon receptors. This three-way activity is the differentiating feature: GLP-1 and GIP components drive satiety, delayed gastric emptying, and glucose-dependent insulin secretion, while the glucagon-receptor arm raises resting energy expenditure and promotes hepatic fatty-acid oxidation. Retatrutide is a synthetic 39-amino-acid peptide with a C20 fatty-acid side chain that binds albumin and yields a half-life supporting once-weekly subcutaneous dosing.

Published trials

The most-cited data set is Eli Lilly's Phase 2 obesity trial: a 48-week, double-blind, randomized study in adults with obesity or overweight with at least one weight-related comorbidity. Reported mean placebo-subtracted body weight reduction at the highest tested dose was in the range of 22–24%, the largest magnitude yet reported for any single-molecule pharmacotherapy in obesity. HbA1c reductions, waist circumference change, and lipid-panel improvements tracked the weight response.

A parallel Phase 2 trial in adults with type 2 diabetes reported placebo- subtracted HbA1c reductions and weight loss consistent with the dose-response pattern seen in the obesity trial. A separate Phase 2 hepatology trial evaluated MASLD (metabolic dysfunction-associated steatotic liver disease) endpoints, with reported reductions in hepatic fat fraction on MRI-PDFF. Phase 3 programs (TRIUMPH) are ongoing at time of writing and had not reported topline data.

Safety profile

Adverse events in published Phase 2 data were predominantly gastrointestinal — nausea, vomiting, diarrhea, constipation — clustered during the dose- escalation window and largely resolving with continued titration. Frequency was dose-dependent. A modest, reversible increase in resting heart rate has been reported, consistent with the glucagon-receptor component. As with the broader incretin class, published literature discusses precautions around history of medullary thyroid carcinoma, multiple endocrine neoplasia type 2, pancreatitis, and diabetic retinopathy. Long-term safety data comparable to semaglutide's outcomes trials is not yet available.

How it compares in its class

Retatrutide sits alongside tirzepatide (dual GLP-1/GIP) and semaglutide (GLP-1 monoagonist) as the third rung of the incretin ladder. In head-to-head analyses of Phase 2 weight-loss magnitude (retatrutide vs. SURMOUNT tirzepatide vs. STEP semaglutide), retatrutide's Phase 2 placebo-subtracted weight loss is the largest reported to date. Whether that advantage will persist in Phase 3, and whether the glucagon-receptor component confers durability or cardiometabolic benefit beyond weight, remains an open trial question.

References

  • PMID: 37356247 — Jastreboff AM et al., "Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial." NEJM 2023;389:514-526.
  • PMID: 37170445 — Rosenstock J et al., Retatrutide Phase 2 trial in type 2 diabetes. Lancet 2023.
  • PMID: 38762741 — Sanyal AJ et al., Retatrutide Phase 2 trial in MASLD/NAFLD, 2024.
  • DOI: 10.1056/NEJMoa2301972 — NEJM Phase 2 obesity paper (Jastreboff 2023).

Buy Retatrutide in Canada: Prescott Bio Canada carries Retatrutide vials — HPLC + mass-spec tested, ships from Richmond BC in 2-4 business days.