Retatrutide

How does Retatrutide work?

Retatrutide is described by its developers' trial reports as a single peptide with agonist activity at three receptors: the glucose-dependent insulinotropic polypeptide (GIP) receptor, the glucagon-like peptide-1 (GLP-1) receptor and the glucagon receptor55PubMedRetatrutide, 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 conducted in the USA. Rosenstock J et al. Lancet. 2023.. The first two are the targets of tirzepatide; glucagon-receptor agonism is the addition. Glucagon signaling is studied for its effects on energy expenditure and hepatic fat handling, which is one reason the program includes a dedicated liver-fat sub-study4.

In the phase 2 liver sub-study, reductions in liver fat tracked changes in body weight, abdominal fat and markers of insulin sensitivity and lipid metabolism4. Whether the glucagon component adds benefit beyond weight loss itself has not been isolated in a published trial.

How long does it last, and how was it scheduled in trials?

Trials administer retatrutide once weekly by subcutaneous injection1. Phase 2 work found that gastrointestinal side effects were partially mitigated by starting at 2 mg rather than 4 mg, which is why later protocols escalate the dose stepwise3. We have not found a peer-reviewed human half-life value in the records we fetched, so none is given here.

What did the clinical trials find?

Obesity without diabetes. The phase 2 trial randomized 338 adults to 1–12 mg or placebo for 48 weeks. At 24 weeks, the 12 mg group's mean weight change was −17.5% versus −1.6% with placebo; at 48 weeks, it was −24.2% versus −2.1%. At 48 weeks, 83% of the 12 mg group had lost at least 15% of body weight, compared with 2% on placebo3. The phase 3 TRIUMPH-1 trial then enrolled 2,339 adults and reported −23.7% (9 mg) and −25.0% (12 mg) at 80 weeks against −3.9% with placebo1.

Type 2 diabetes. In the phase 2 diabetes trial (281 participants across 42 US centers), HbA1c fell by up to 2.02 percentage points at 24 weeks with the 12 mg escalation arm, versus −1.41 with the active comparator dulaglutide 1.5 mg5. Phase 3 TRANSCEND-T2D-1 (537 participants) reported HbA1c reductions of 1.69–1.94 points against 0.81 with placebo at 40 weeks, with body-weight reductions of 11.5–15.3%66PubMedEfficacy and safety of retatrutide, a GIP, GLP-1, and glucagon receptor agonist, in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1): a double-blind, randomised, phase 3 trial. Bajaj HS et al. Lancet. 2026.. TRIUMPH-2, in 1,152 people with both obesity and type 2 diabetes, reported up to −18.8% weight change at 80 weeks2.

Body composition. A DXA sub-study of the phase 2 diabetes trial measured total fat mass by DXA at 36 weeks: it fell 26.1% with the pooled 8 mg groups and 23.2% with 12 mg, versus 4.5% with placebo and 2.6% with dulaglutide. The investigators reported that the proportion of lean mass lost relative to total weight lost was similar to other obesity treatments77PubMedEffects of retatrutide on body composition in people with type 2 diabetes: a substudy of a phase 2, double-blind, parallel-group, placebo-controlled, randomised trial. Coskun T et al. Lancet Diabetes Endocrinol. 2025..

The design of the phase 3 program. TRIUMPH uses a "basket" design: obstructive sleep apnea and knee-osteoarthritis protocols are nested inside the weight-management trials, with a separate cardiovascular-disease population (TRIUMPH-3) and a stand-alone osteoarthritis trial (TRIUMPH-4), totaling more than 5,800 participants88PubMedRetatrutide for the treatment of obesity, obstructive sleep apnea and knee osteoarthritis: Rationale and design of the TRIUMPH registrational clinical trials. Giblin K et al. Diabetes Obes Metab. 2026..

What adverse events were reported in trials?

Across trials the dominant adverse events were gastrointestinal. In TRIUMPH-2, diarrhea occurred in 27–34% of retatrutide participants versus 13% on placebo, and nausea in 14–28% versus 8%2. The same trial reported hypotension in up to 6% and dysesthesia (abnormal skin sensation) in up to 7% of retatrutide participants, versus under 1% and 1% on placebo. Permanent discontinuation due to adverse events or death was 12% at 9 mg and 8% at 12 mg, compared with 5% on placebo; the investigators judged all deaths unrelated to the study drug2.

In TRANSCEND-T2D-1, discontinuation due to adverse events was 2–5% with retatrutide and 0% with placebo, and no severe hypoglycemia was reported6. A dose-dependent rise in heart rate that peaked at 24 weeks and declined thereafter was reported in the phase 2 obesity trial3.