Retatrutide

Retatrutide (developmental code LY3437943) is an investigational once-weekly injectable peptide from Eli Lilly that activates three metabolic hormone receptors at once: GIP, GLP-1, and the glucagon receptor. It is a clinical-stage compound — pivotal phase 3 trials are running, but it is not approved anywhere in the world for any use.

Two facts define retatrutide right now. First, its phase 2 obesity trial produced the most striking weight-loss result yet published for a single agent: a mean reduction of 24.2% of body weight at 48 weeks on the highest dose, with weight still falling when the trial ended (Jastreboff et al., NEJM 2023, n=338). Second, because no regulator has approved it, every vial sold as "retatrutide" today is unapproved gray-market product. There is no pharmacy version, no legitimate retail supply, and no independent verification of what those vials contain.

Retatrutide is a single peptide engineered to act as an agonist at three receptors that its approved relatives cover only partially: semaglutide activates the GLP-1 receptor alone, and tirzepatide adds GIP. Each arm contributes something different:

• GLP-1 receptor: suppresses appetite, slows gastric emptying, and enhances glucose-dependent insulin secretion — the "eat less" pathway shared by the whole incretin class.

• GIP receptor: adds complementary insulinotropic and appetite effects, and appears to improve gastrointestinal tolerability of the combination.

• Glucagon receptor: the new piece. Glucagon signaling increases energy expenditure and drives the liver to oxidize fat — a "burn more" arm layered on top of the "eat less" pharmacology, and the leading explanation for retatrutide's unusually deep effects on weight and liver fat (Sanyal et al., Nature Medicine 2024).

The glucagon arm is also a balancing act: glucagon raises blood glucose, so a triple agonist has to pair it with enough incretin activity to keep glycemic control moving in the right direction. The phase 2 diabetes trial suggests the balance works — HbA1c fell by about 2 percentage points at the top dose (Rosenstock et al., The Lancet 2023).

Retatrutide has no approved indication in any country. Its clinical program targets the conditions where triple agonism is hypothesized to matter most:

• Obesity and overweight (the phase 3 TRIUMPH program).
• Type 2 diabetes (phase 2 and phase 3 TRANSCEND trials).
• Metabolic dysfunction-associated steatotic liver disease (MASLD), via a dedicated liver-fat substudy.
• Obesity-linked conditions such as knee osteoarthritis and obstructive sleep apnea, folded into the TRIUMPH master protocol (NCT05929066).

Outside those trials, retatrutide circulates heavily as a gray-market "research chemical." The FDA has warned specifically about unapproved GLP-1 class drugs sold for weight loss outside the regulated supply chain (FDA). For retatrutide the situation is starker than for compounded semaglutide: there is no approved reference product at all, so nothing sold under this name has passed any regulatory quality bar.

The trial safety picture so far looks like the incretin class, with one signal specific to the added pharmacology:

• Gastrointestinal effects — nausea, vomiting, diarrhea, constipation — were the most common adverse events in the phase 2 obesity trial, were dose-related, and were mostly mild to moderate (NEJM 2023). In the phase 2 diabetes trial, 35% of retatrutide-treated participants reported GI events (The Lancet 2023).

• Heart-rate increase — in the obesity trial, heart rate rose on treatment, peaking around 24 weeks and declining thereafter. This is watched closely because glucagon-receptor agonism can raise heart rate beyond what GLP-1 drugs alone do, and it is a standing monitoring item in the trial protocols.

• Hypoglycemia — no severe hypoglycemia and no deaths were reported in the phase 2 diabetes trial.

What is not known matters just as much: long-term cardiovascular and kidney outcomes are exactly what the dedicated phase 3 outcomes trial (TRIUMPH-Outcomes, NCT06383390) is designed to establish, and it has not reported. Gray-market vials add a separate layer of risk — unverified identity, purity, and sterility — on top of an incompletely characterized drug. See the side-effects page for a fuller discussion.

Retatrutide is administered as a once-weekly subcutaneous injection in all of its clinical trials; its pharmacokinetics support weekly dosing the same way they do for semaglutide and tirzepatide.

Trial protocols also include monitoring — heart rate, glycemic measures, adverse-event tracking — that has no counterpart in self-directed use of gray-market material. More context is on the dosing-education page.

The only legitimate retatrutide is the sponsor's trial material, supplied inside clinical studies. There is no pen device, no pharmacy vial, and no authorized generic anywhere. Vials sold online under codes like "RT10" are unapproved products whose contents no regulator has verified.

Within the incretin family, retatrutide is best understood by receptor count: semaglutide (GLP-1 only, approved), tirzepatide (GLP-1 + GIP, approved), retatrutide (GLP-1 + GIP + glucagon, investigational). The head-to-head differences are laid out in tirzepatide vs retatrutide. Retatrutide is studied as a standalone agent; it is not part of any studied combination product.

The published record is unusually strong for a drug this early, which is why it dominates search interest despite having no approval:

• Phase 2, obesity (n=338, 48 weeks): mean weight change from −8.7% (1 mg) to −24.2% (12 mg) vs −2.1% for placebo; the 12 mg arm was −17.5% at the 24-week primary endpoint, so weight was still falling steeply through the second half of the trial (Jastreboff et al., NEJM 2023).

• Phase 2, type 2 diabetes (n=281, 36 weeks): HbA1c −2.02% at 12 mg at 24 weeks, superior to placebo and dulaglutide; weight −16.94% at 36 weeks (Rosenstock et al., The Lancet 2023).

• Phase 2a, MASLD substudy (n=98): mean relative liver-fat reduction of just over 80% at the 8 mg and 12 mg doses at 24 weeks; 86% of the 12 mg group reached normal liver-fat levels (Sanyal et al., Nature Medicine 2024).

• Phase 3: the TRIUMPH obesity program — TRIUMPH-1 (n=2,335, completed), TRIUMPH-3 (severe obesity with cardiovascular disease, n=1,946, completed), TRIUMPH-4 (obesity with knee osteoarthritis, completed), and the ongoing TRIUMPH-Outcomes cardiovascular and kidney outcomes trial. The first phase 3 results in type 2 diabetes (TRANSCEND-T2D-1, n=537) published in 2026 (Bajaj et al., The Lancet 2026).

For deeper dives on this peptide, see:

• Retatrutide benefits and areas of interest
• Retatrutide side effects and safety context
• Retatrutide dosing concepts (educational)
• Retatrutide research and evidence overview

Is retatrutide approved? No. As of August 2026, retatrutide is not approved by the FDA, EMA, or any other regulator, for any indication, anywhere in the world. It is available legitimately only inside clinical trials, and anything sold under the name is unapproved gray-market product.

What did the retatrutide trial actually show? In the phase 2 obesity trial (n=338), the 12 mg weekly dose produced a mean weight reduction of 24.2% at 48 weeks versus 2.1% for placebo, and the weight-loss curves had not flattened when the trial ended (NEJM 2023). That is the largest reduction reported for any single agent in a randomized trial to date — but it is a 338-person, 48-week study, not a completed approval package.

How is retatrutide different from tirzepatide? Tirzepatide activates two receptors (GLP-1 and GIP); retatrutide adds a third, the glucagon receptor, which is thought to raise energy expenditure and accelerate liver-fat clearance. Tirzepatide is an approved medicine with completed phase 3 programs; retatrutide is still investigational. See the full tirzepatide vs retatrutide comparison.

What is the phase 3 status? The pivotal TRIUMPH obesity trials — including TRIUMPH-1 (n=2,335) and TRIUMPH-3 (n=1,946) — are listed as completed on ClinicalTrials.gov, a long-term cardiovascular and kidney outcomes trial is ongoing, and the first phase 3 results in type 2 diabetes published in The Lancet in 2026.

When could retatrutide be approved? No approval has been announced and no regulator has publicly committed to a decision date. With pivotal trials completed or reporting, a regulatory submission is the logical next step, but review timing is the regulator's call. Any specific approval date circulating online is speculation.

Is the retatrutide sold online real? There is no legitimate retail supply — the manufacturer sells retatrutide to no one outside its trials. Vials sold as "retatrutide" are unregulated products whose identity, dose accuracy, and sterility are unverified, a category the FDA has warned about for unapproved GLP-1 class drugs (FDA).

Does retatrutide reduce liver fat? In a 98-person phase 2a substudy of participants with MASLD, the 8 mg and 12 mg doses cut liver fat by just over 80% on average at 24 weeks, and 86% of the 12 mg group reached normal liver-fat levels (Nature Medicine 2024). Liver-related benefit remains an investigational finding, not an approved indication.