Retatrutide (LY3437943) is not approved by the FDA or any other regulator. The results below come from clinical trials; they are not approved benefits, and anything sold as retatrutide today is unapproved gray-market material.
Overview
The benefits being studied for retatrutide are large reductions in body weight, blood glucose, and liver fat. In its phase 2 obesity trial, the highest dose produced a mean weight loss of 24.2% at 48 weeks — the largest reduction yet reported for a single agent in a randomized trial (Jastreboff et al., NEJM 2023). Separate trials have reported HbA1c reductions of about 2 percentage points in type 2 diabetes and liver-fat reductions above 80% in fatty liver disease. Every one of these findings is investigational: retatrutide is a clinical-stage drug with no approval anywhere.
Weight loss — the headline result
The phase 2 obesity trial randomized 338 adults to once-weekly retatrutide (1–12 mg) or placebo for 48 weeks (NEJM 2023):
- Mean weight change ranged from −8.7% (1 mg) to −24.2% (12 mg), versus −2.1% for placebo.
- At 48 weeks, 60–83% of participants on active doses lost at least 15% of body weight, versus 2% on placebo.
- The 12 mg arm was −17.5% at 24 weeks and −24.2% at 48, so weight was still falling steeply when the trial ended — whether longer treatment produces more loss is what phase 3 is testing.
For scale: approved incretin drugs like semaglutide and tirzepatide produced roughly 15% and 20–21% mean weight loss in their own longer pivotal trials. Cross-trial comparisons are unreliable — different populations, durations, and designs — but the phase 2 number is why retatrutide draws so much attention.
Glucose control in type 2 diabetes
In the phase 2 type 2 diabetes trial (n=281, 36 weeks), retatrutide 12 mg reduced HbA1c by 2.02 percentage points at 24 weeks — superior to both placebo and the GLP-1 drug dulaglutide — while reducing body weight by 16.94% at 36 weeks (Rosenstock et al., The Lancet 2023). The first phase 3 diabetes results (TRANSCEND-T2D-1, n=537) broadly confirmed the pattern: HbA1c fell 1.94 points and weight fell 15.3% at 40 weeks on 12 mg (Bajaj et al., The Lancet 2026). Notably, no severe hypoglycemia was reported in either trial.
Liver fat
A 98-person phase 2a substudy enrolled participants with metabolic dysfunction-associated steatotic liver disease (MASLD) and at least 10% liver fat (Sanyal et al., Nature Medicine 2024):
- Mean relative liver-fat reduction at 24 weeks: −42.9% (1 mg), −57.0% (4 mg), −81.4% (8 mg), −82.4% (12 mg), versus +0.3% for placebo.
- At 24 weeks, 86% of the 12 mg group achieved normal liver-fat levels (under 5%), versus none on placebo.
This is the endpoint where the glucagon-receptor arm is expected to matter most, because glucagon signaling acts directly on hepatic fat metabolism.
Why the third receptor matters
Retatrutide's design thesis is that adding glucagon-receptor agonism to the GLP-1 and GIP activity of drugs like tirzepatide changes the mechanism from "eat less" to "eat less and burn more":
- GLP-1 and GIP activity suppress appetite and support insulin secretion.
- Glucagon-receptor activity increases energy expenditure and drives hepatic fat oxidation.
- The trade-offs — a heart-rate increase and glucagon's glucose-raising effect — are covered on the side-effects page.
How the three arms compare in practice against the approved dual agonist is discussed in tirzepatide vs retatrutide.
Status and limits
All of the above comes from phase 2 studies and one phase 3 diabetes trial; the pivotal phase 3 obesity results and the long-term cardiovascular outcomes trial (TRIUMPH-Outcomes) will determine whether the phase 2 numbers hold at scale. Until a regulator approves it, retatrutide has no established benefit in the medical sense — and no legitimate product exists outside its trials. The research-evidence page tracks the full program.