Retatrutide: the incretin landscape, charted compound by compound.

In plain English

Retatrutide is a new kind of weight-loss drug candidate — not yet approved anywhere, still being tested in large clinical trials. What makes it different from earlier options is that it works on three hormone signals at once: GLP-1 (which curbs appetite and helps regulate blood sugar), GIP (which also helps control insulin and affects fat cells), and glucagon (which makes your body burn more energy). Most earlier drugs in this class targeted just one or two of those signals. In the biggest Phase 2 study completed so far, the highest-tested amount caused an average 24.2% reduction in body weight over 48 weeks — a number that drew wide attention in the research community. The trials are ongoing; regulators have not approved it for any use. This site summarizes what the published studies have found — the promising numbers, the safety signals, and what is still unknown. What people have reported using research-labeled material — including downsides — is on the effects page.

What does retatrutide do

Retatrutide (LY3437943) activates three receptors simultaneously: GLP-1R (glucagon-like peptide-1 receptor), GIPR (glucose-dependent insulinotropic polypeptide receptor), and GCGR (glucagon receptor). The GLP-1 and GIP arms suppress appetite and enhance glucose-dependent insulin secretion. The glucagon arm adds a layer the dual agonists lack: increased energy expenditure (the rate at which the body burns calories) and accelerated hepatic lipid (liver-fat) metabolism ^[1].

In a 48-week Phase 2 obesity trial enrolling 338 adults, once-weekly subcutaneous retatrutide at 12 mg produced a mean body-weight change of -24.2% versus -2.1% with placebo ^[1]. In a parallel 36-week Phase 2 trial in type 2 diabetes, 12 mg lowered HbA1c (glycated hemoglobin — a three-month blood-sugar average) by -2.02 percentage points and reduced body weight by -16.94% versus placebo ^[2]. A dedicated 48-week Phase 2 substudy in participants with MASLD (metabolic dysfunction-associated steatotic liver disease, the current clinical term for fatty liver linked to metabolic risk) found retatrutide 12 mg cut liver fat by -82.4% at 24 weeks, with 86% reaching normal liver-fat levels below 5% ^[5].

These figures come from controlled Phase 2 trials. Phase 3 studies (the TRIUMPH program) are ongoing and have not yet published results. No regulator has approved retatrutide for any indication as of mid-2026.

How does retatrutide work

Cryo-EM structural studies resolved retatrutide's engagement with all three receptors at near-atomic resolution (2.68/3.26/2.84 Å). Relative to the endogenous hormones themselves, retatrutide is approximately 8.9× more potent at GIPR (glucose-dependent insulinotropic polypeptide receptor) but ~0.3× and ~0.4× at GCGR and GLP-1R respectively ^[3]. This tuning — high GIP potency, partial glucagon activation — is deliberate: full glucagon agonism raises blood glucose; partial agonism drives energy expenditure without triggering hyperglycemia.

The downstream signal at all three receptors is cAMP/PKA (cyclic adenosine monophosphate/protein kinase A) — a second-messenger cascade common to class-B G protein-coupled receptors (GPCRs, a large family of receptors that relay hormone signals through the cell membrane). The net effect observed in trials is appetite reduction, improved glucose regulation, increased caloric burn, and substantial liver-fat clearance. How these signals coordinate inside a single molecule is the subject of the cryo-EM structural analysis ^[3].

The first-in-human Phase 1b study established retatrutide's pharmacokinetics (PK — how the body handles the drug over time): a half-life of approximately 6 days supports once-weekly subcutaneous dosing ^[4]. The highest-dose group in that 12-week study lost -8.96 kg placebo-adjusted.

Retatrutide results — what Phase 2 measured

The headline Phase 2 obesity result: -24.2% mean body weight at 48 weeks (12 mg once weekly) versus -2.1% placebo ^[1]. To situate this on the incretin landscape, a 2024 comparative review covering seven GLP-1 receptor agonists and polyagonists ranked retatrutide among the highest-efficacy agents studied ^[7]. A 2026 network meta-analysis of randomized controlled trials ranked retatrutide highest for both weight and HbA1c reduction versus placebo, with only retatrutide reaching statistical significance for HbA1c among the glucagon receptor agonists analyzed ^[11].

In the diabetes Phase 2 trial, HbA1c fell -2.02 percentage points from baseline at 24 weeks, and body weight fell -16.94% by week 36 ^[2]. GI adverse events (nausea, vomiting, diarrhea, constipation) occurred in ~35% of participants and were mostly mild to moderate; no severe hypoglycemia and no deaths were recorded ^[2].

A 2025 review characterized the ~24% weight loss as "a step-change versus prior incretin therapies," noting that no previously approved compound in the GLP-1 class had produced this magnitude of loss in a Phase 2 program ^[6].

For a direct head-to-head comparison of retatrutide against tirzepatide (a dual GIP/GLP-1 agonist), see the retatrutide vs tirzepatide page. For the semaglutide comparison, see is retatrutide better than semaglutide.

Is retatrutide fda approved

No. Retatrutide is not FDA-approved and not approved by any regulatory agency as of mid-2026. It is an investigational compound. The active Phase 3 program (TRIUMPH) includes trials in obesity, type 2 diabetes, cardiovascular outcomes, chronic kidney disease (TRANSCEND-CKD ^[10]), and an active-comparator trial directly pitting retatrutide against tirzepatide (NCT06662383 ^[8]). A 2024 Clinical Diabetes profile described retatrutide as "the first triple agonist developed for anti-obesity therapy" — noting its investigational status explicitly ^[9].

Retatrutide availability outside clinical trials does not exist through any approved channel. Research-labeled material sold outside trials is unregulated, of unverified identity and purity, and outside clinical oversight. The FDA issued warning letters to gray-market retatrutide vendors in 2025 citing Federal FD&C Act violations.

Retatrutide availability and when will retatrutide be available

Retatrutide is available only through clinical trials as of mid-2026. The Phase 3 TRIUMPH program (in obesity, type 2 diabetes, cardiovascular outcomes, and CKD) is ongoing; no results from these Phase 3 trials have been published. A dedicated head-to-head Phase 3 trial versus tirzepatide (NCT06662383) is enrolled and running ^[8].

Timeline to potential regulatory approval depends on Phase 3 results, which have not been published. No official approval date has been announced. Eli Lilly, the developer, has stated Phase 3 enrollment timelines consistent with potential NDA submission in the 2026-2027 window — but this is subject to trial outcomes and regulatory review and cannot be confirmed here.