Retatrutide vs Semaglutide: What the Trials Actually Show

By Evan Marsh, EditorUpdated August 7, 2026Phase 2/3 trial data, matched estimand for estimand

This is the widest gap in the incretin class on the scale — and the narrowest on evidence quality. Retatrutide reports weight reductions roughly ten points larger than semaglutide's. Semaglutide is the only drug in this comparison that has shown it prevents heart attacks and strokes. Both statements are true, and which one matters more depends on the question being asked.

The short answer

For weight reduction alone, retatrutide's trial numbers are far larger. For everything else — approval, prescribability, the depth of the safety record, and hard clinical outcome data — semaglutide is ahead by a distance no weight percentage closes. There has never been a head-to-head trial between them.

Side by side

	Retatrutide	Semaglutide
Receptor targets	GIP + GLP-1 + glucagon	GLP-1 only
Status	Phase 3; BLA submission stated for Q1 2027	FDA approved (Wegovy, Ozempic, Rybelsus)
Pivotal obesity trial	TRIUMPH-1, n=2,339, 80 weeks	STEP-1, n=1,961, 68 weeks
Weight change, counting everyone randomized	−25.0%	−14.9%
Cardiovascular outcome data	None	Yes — approved to reduce major adverse cardiovascular events
Other approved indications	None	Type 2 diabetes; noncirrhotic MASH with fibrosis (accelerated approval)
Oral formulation	No	Yes (tablets)
Peer-reviewed?	Phase 2 yes; Phase 3 topline only	Yes — NEJM 2021, plus a large follow-on literature
Can a doctor prescribe it?	No	Yes

Mean body-weight reduction, counting every participant randomised

InvestigationalFDA approved

Retatrutide 12 mgTRIUMPH-1, 80 weeks

25.0%

Semaglutide 2.4 mgSTEP-1, 68 weeks

14.9%

Both bars use the same analysis. Every obesity trial reports two numbers: one counting all randomized participants whether or not they stayed on the drug, and one assuming full adherence. Lilly calls these treatment-regimen and efficacy; Novo Nordisk calls the same pair treatment policy and trial product. Retatrutide's widely quoted 28.3% belongs to the second convention and cannot be placed beside STEP-1's first-convention 14.9% — doing so inflates the gap by two to three points. The chart above compares like with like.

What semaglutide has that retatrutide does not

The weight numbers are the least interesting part of this comparison. Semaglutide has accumulated something no investigational compound can have yet:

Hard outcome data. It is approved to reduce the risk of major adverse cardiovascular events in adults with established cardiovascular disease and obesity — evidence that it changes what happens to people, not just what the scale says.
Indication breadth. Type 2 diabetes, and an accelerated approval in noncirrhotic MASH with moderate-to-advanced fibrosis.
Discontinuation data. The STEP-1 extension documented substantial weight regain after stopping — unwelcome information that the sponsor published anyway. No equivalent data exists for retatrutide.
Years of post-marketing surveillance across a far larger and less selected population than any trial enrolls.

Retatrutide's counterpart list is short: larger weight reduction, a Phase 2a liver-fat result, and sub-study findings in sleep apnea and knee osteoarthritis. All of it is preliminary by comparison.

Mechanism: one receptor versus three

Semaglutide's single-receptor action works through appetite and satiety. Retatrutide adds GIP, and then glucagon — which raises energy expenditure and mobilizes hepatic fat instead of further suppressing appetite. Stacking distinct mechanisms is why the weight curve goes further. It is also why retatrutide's trials monitored heart rate and liver enzymes more closely than a GLP-1-only program needs to.

Side effects

Both are dominated by gastrointestinal effects worst during titration. Semaglutide's label carries the class boxed warning for thyroid C-cell tumors observed in rodents, with contraindications for personal or family history of medullary thyroid carcinoma or MEN 2. Retatrutide's Phase 3 program reported diarrhea as the most common complaint rather than nausea, plus a dose-related dysesthesia signal that has no counterpart in the semaglutide label. Detail on theretatrutide side effects page.

Practical difference

Semaglutide is obtainable with a prescription, dispensed by a pharmacy, monitored by a clinician, and often partly covered. Retatrutide has no prescription pathway and no legal compounding route; the only supervised access is a clinical trial. Ouraccess and approval page covers the routes and the timeline, and the full GLP-1 comparison tableputs every compound in the class side by side on one consistent analysis.

Frequently asked questions

Is retatrutide better than semaglutide for weight loss?

The reported weight reductions are substantially larger — roughly 25% versus 15% on matched analyses. But semaglutide is approved, prescribable, and uniquely backed by a cardiovascular outcomes trial showing it reduces major adverse cardiac events. Retatrutide has bigger weight numbers and no outcome data at all.

What is the difference between retatrutide and semaglutide?

Semaglutide activates one receptor, GLP-1. Retatrutide activates three: GIP, GLP-1 and glucagon. Semaglutide is approved as Wegovy and Ozempic with indications spanning weight, cardiovascular risk and liver disease; retatrutide is in Phase 3 with no approval anywhere.

Why does semaglutide have lower weight loss numbers?

Single-receptor activation works through appetite and satiety alone. The dual and triple agonists add mechanisms — GIP, and in retatrutide's case glucagon-driven energy expenditure. More mechanisms, larger effect on the scale. That does not automatically mean better health outcomes, which is a separate question with separate evidence.

Does weight come back after stopping either drug?

Yes — this is well documented for semaglutide, where the STEP-1 trial extension showed substantial regain after withdrawal. No published discontinuation data exists for retatrutide. There is no reason to expect it behaves differently.

Which is safer?

Semaglutide has by far the larger safety database, including years of post-marketing use and a completed cardiovascular outcomes trial. Both carry the class gastrointestinal profile. Retatrutide additionally showed a dose-related dysesthesia signal in Phase 3, and its safety record ends where its trials end.

Sources

Wilding JPH et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1). New England Journal of Medicine, 2021;384(11):989–1002. PubMed
Wilding JPH et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes, Obesity and Metabolism, 2022;24(8):1553–1564. PubMed
Jastreboff AM et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine, 2023;389(6):514–526. PubMed
Eli Lilly. TRIUMPH-1 topline results, 21 May 2026. Company announcement. Not peer-reviewed.
WEGOVY (semaglutide) prescribing information — indications, dose strengths and boxed warning. DailyMed label
Registry records: TRIUMPH-1 (NCT05929066).

Related guides

Research use only. Retatrutide is investigational and not approved for human use. This page compares published trial data and is not medical advice; decisions about approved medicines belong with a physician.