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This thread answers the most common questions about Retatrutide research for members of this forum. It’s meant as a starting reference point for the Retatrutide (GLP-3) Research & Experiences forum — for anything not covered here, feel free to start a new discussion thread.

What is Retatrutide?

Retatrutide (Eli Lilly compound LY3437943) is an investigational once-weekly injectable compound studied for obesity, overweight, and type 2 diabetes. It is currently in Phase 3 clinical development (Lilly’s TRIUMPH and TRANSCEND research programs) and is not FDA-approved and not available by prescription for any indication as of this writing. Any information in this forum reflects published research and public trial reporting, not real-world clinical use.

Why do people call it “GLP-3”?

You’ll see Retatrutide referred to informally as “GLP-3” in online research communities, including sometimes here. It’s worth being precise about this: “GLP-3” is not an official scientific or regulatory classification — there is no recognized “GLP-3 receptor” in endocrinology, and Lilly, the FDA, and the peer-reviewed literature do not use that term. The nickname comes from Retatrutide acting on three separate metabolic receptor pathways (GLP-1, GIP, and glucagon) rather than one (like semaglutide) or two (like tirzepatide) — so people shorthand it as a step beyond “GLP-1” and “GLP-2.” In the actual research literature, it’s described as a triple hormone receptor agonist or “tri-agonist.”

What does “triple agonist” actually mean?

Retatrutide is a single molecule engineered to activate three different receptors at once: the GLP-1 receptor, the GIP receptor, and the glucagon receptor. In published Phase 2 research, this combination was associated with appetite suppression and improved insulin signaling (via GLP-1 and GIP) alongside increased energy expenditure and liver fat reduction (linked to glucagon receptor activity). The rationale for combining all three is discussed in the original Phase 2 publication linked below.

What’s the current research status?

As of mid-2026, Retatrutide has completed Phase 2 testing and is in Phase 3 (the TRIUMPH program for obesity/overweight and TRANSCEND program for type 2 diabetes). Lilly has reported positive topline Phase 3 results for TRIUMPH-1 (obesity) and TRANSCEND-T2D-1 (type 2 diabetes) in 2026, with a cardiovascular/kidney outcomes trial (TRIUMPH-Outcomes) and a head-to-head trial against tirzepatide still ongoing. Based on public reporting, an FDA filing is anticipated in late 2026, which would put a possible approval decision in 2027 or later — but timelines can and do change, and none of this is guaranteed.

How is it different from semaglutide?

Semaglutide (marketed as Ozempic and Wegovy) is FDA-approved and activates only the GLP-1 receptor. In its pivotal STEP 1 trial, semaglutide 2.4 mg produced average weight loss of about 14.9% at 68 weeks. Retatrutide targets GLP-1, GIP, and glucagon receptors together, and in its own separate Phase 2 and Phase 3 trials has shown larger average weight loss than semaglutide’s published trials. These are results from separate studies in different patient populations, not a head-to-head comparison, so the percentages aren’t directly interchangeable.

How is it different from tirzepatide?

Tirzepatide (marketed as Mounjaro and Zepbound) is FDA-approved and activates two receptors: GLP-1 and GIP. Its SURMOUNT-1 trial showed average weight loss of about 22.5% at the 15 mg dose over 72 weeks. Retatrutide adds glucagon receptor activity on top of GLP-1 and GIP. A real head-to-head trial comparing Retatrutide directly against tirzepatide is currently running (ClinicalTrials.gov NCT06662383), with results expected around the end of 2026 — until then, any Retatrutide-vs-tirzepatide percentage comparison you see (including in this forum) is a cross-trial comparison, not a direct one, and should be read with that caveat.

For deeper compound-specific discussion, see Tirzepatide Research & Experiences and Semaglutide Research & Experiences, both part of GLP Research & Experiences.

Where can I read the actual trial data?

• Phase 2 obesity trial (NEJM, 2023): Triple-Hormone-Receptor Agonist Retatrutide for Obesity
• Phase 2a liver fat (MASLD) trial (Nature Medicine): Retatrutide for metabolic dysfunction-associated steatotic liver disease
• TRIUMPH-1 (Phase 3, obesity/overweight): ClinicalTrials.gov NCT05929066
• TRANSCEND-T2D-1 (Phase 3, type 2 diabetes): ClinicalTrials.gov NCT06354660
• TRIUMPH-Outcomes (cardiovascular & kidney outcomes): ClinicalTrials.gov NCT06383390
• Head-to-head vs. tirzepatide (ongoing): ClinicalTrials.gov NCT06662383

Educational disclaimer: This FAQ and this forum are for research and informational discussion only. Nothing here is medical advice, a treatment recommendation, or a substitute for care from a licensed healthcare professional. Retatrutide is investigational and not approved for medical use.

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