Educational information only. Not medical advice.

Research Memos

Retatrutide vs semaglutide

Retatrutide activates GIP, GLP-1 and glucagon receptors; semaglutide activates GLP-1 receptors. Separate placebo-controlled obesity trials found substantial weight loss with each, but their percentages cannot establish which works better in a shared population. Semaglutide has approved products and cardiovascular-outcome evidence. Retatrutide remains investigational, with a direct semaglutide diabetes comparison registered but no result report located for this review.

Research reviewed October 15, 2026. Educational information only.

One shared receptor and two additional targets

Both compounds activate the receptor for glucagon-like peptide-1, or GLP-1, a hormone involved in appetite and glucose-dependent insulin release. Retatrutide is one engineered peptide that also activates receptors for glucose-dependent insulinotropic polypeptide, GIP, and glucagon. The three targets provide a biological rationale for studying changes in appetite, glucose regulation and energy use. Counting targets alone cannot predict the balance of clinical benefit and adverse effects.

Semaglutide’s clinical evidence comes from specific tablets and injections used in specific populations. Retatrutide’s trials have used investigational injections. The current Wegovy label and Jastreboff and colleagues’ 2026 trial establish those different settings.

The main differences

How much weight did people lose in the separate obesity trials?

These were two placebo-controlled trials in adults without diabetes. TRIUMPH-1 studied 2,339 adults with obesity over 80 weeks; STEP 1 studied 1,961 adults with obesity or overweight plus a weight-related condition over 68 weeks. Both main estimates account for treatment stopping. They are not a head-to-head comparison.

Retatrutide

TRIUMPH-1 reported average weight loss of 17.6%, 23.7% and 25.0% in the 4-, 9- and 12-mg groups versus 3.9% with placebo at 80 weeks. The two higher-dose differences from placebo were 19.8 and 21.0 percentage points (P<0.001 for both). These figures cannot establish superiority to semaglutide.

Sources

Semaglutide

STEP 1 reported average loss of 14.9% with weekly 2.4-mg semaglutide versus 2.4% with placebo at 68 weeks. The difference was 12.4 percentage points (95% confidence interval 11.5–13.4). The result concerns that study’s population, formulation and follow-up.

Sources

How do the receptor targets differ?

GLP-1 is involved in appetite and glucose-dependent insulin release. Each compound is an engineered peptide; the receptor targets describe how it acts and do not themselves measure clinical benefit.

Retatrutide

One peptide activates GIP, GLP-1 and glucagon receptors. This combination motivated the clinical studies of body weight and metabolic outcomes; three receptor targets do not establish a greater benefit than another medicine.

Sources

Semaglutide

Semaglutide activates the GLP-1 receptor. Its clinical effects have been measured with specific oral and injectable products; the approved indications depend on the product.

Sources

What evidence addresses cardiovascular events?

A cardiovascular-outcome trial counts events such as heart attacks and strokes. Weight-loss percentages cannot substitute for that outcome. SELECT enrolled adults with established cardiovascular disease and excess weight, without diabetes; its mean follow-up was 39.8 months.

Retatrutide

The TRIUMPH-1 obesity trial measured weight and selected knee-pain and sleep-apnea outcomes. It did not establish a retatrutide-versus-semaglutide difference in cardiovascular death, heart attack or stroke.

Sources

Semaglutide

In SELECT, cardiovascular death, nonfatal heart attack or nonfatal stroke occurred in 569/8,803 (6.5%) with semaglutide 2.4 mg and 701/8,801 (8.0%) with placebo. The hazard ratio was 0.80 (95% confidence interval 0.72–0.90). This supports benefit against placebo in that population.

Sources

What do pharmacokinetic studies show about time in blood?

Elimination half-life is the time blood concentration takes to fall by half during its terminal decline. The estimates come from human pharmacokinetic studies or the approved product label, not from the weight-loss percentages.

Retatrutide

Urva and colleagues’ phase 1b trial measured retatrutide after subcutaneous injections in adults with type 2 diabetes and reported a half-life of approximately six days. The abstract gives no numerical interval around that estimate.

Sources

Semaglutide

The current Wegovy label reports an elimination half-life of approximately one week. Oral and injected semaglutide differ in absorption; the STEP 1 and SELECT results above concern 2.4-mg weekly injections. Similar elimination times do not establish equal effects.

Sources

Can these sources show which is safer?

The obesity studies did not randomly assign people between retatrutide and semaglutide. Trial events and current product warnings answer different safety questions; they cannot be used as a direct rate comparison.

Retatrutide

Digestive events were common in the trials. The earlier phase 2 trial also recorded dose-related pulse increases that peaked at 24 weeks and declined afterward. Retatrutide remains investigational; these studies do not establish its long-term safety relative to semaglutide.

Sources

Semaglutide

The approved label addresses digestive effects and important pancreatic, gallbladder, kidney and other risks. Its boxed warning concerns thyroid C-cell tumors in rodents, with uncertain human relevance. It contraindicates use in people with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2. No direct safety comparison with retatrutide is established here.

Sources

The obesity percentages come from separate trials

In the published TRIUMPH-1 trial, Jastreboff and colleagues randomized 2,339 adults with obesity and without diabetes to retatrutide or placebo for 80 weeks. The main analysis estimated weight change according to assigned treatment, including people who stopped it. Mean loss was 17.6%, 23.7% and 25.0% across the 4-, 9- and 12-mg groups, compared with 3.9% with placebo. The two higher-dose comparisons with placebo met the prespecified statistical tests. These are the published main-analysis results, distinct from larger estimates reported under an assumption of continued treatment.

Wilding and colleagues’ STEP 1 trial randomized 1,961 adults with obesity, or overweight plus a weight-related condition, without diabetes. Both groups received lifestyle support. At 68 weeks, mean weight loss was 14.9% with weekly semaglutide 2.4 mg and 2.4% with placebo; the estimated difference was 12.4 percentage points (95% confidence interval 11.5–13.4). Its main analysis likewise accounted for treatment stopping. The separate populations, follow-up lengths and treatment plans prevent subtracting these headline percentages to obtain a retatrutide-versus-semaglutide treatment effect.

A direct diabetes comparison is registered

Lilly lists TRANSCEND-T2D-2 as a direct comparison of retatrutide with semaglutide in adults whose type 2 diabetes remains inadequately controlled with metformin, with or without an SGLT2 inhibitor, another glucose-lowering medicine. No outcome report from that comparison was identified in this review’s October 15, 2026 primary and official-source search. A registered study tells readers what is being tested; it does not yet establish a result.

That population also differs from the adults without diabetes in the two obesity trials above. A future glucose result would need its own formulations, doses, follow-up and analysis explained before being applied to weight management.

Weight and cardiovascular events are different outcomes

Semaglutide has evidence for a clinical outcome beyond weight. In Lincoff and colleagues’ SELECT trial, 17,604 adults with established cardiovascular disease and overweight or obesity, without diabetes, received semaglutide 2.4 mg or placebo. Over a mean 39.8 months, cardiovascular death, nonfatal heart attack or nonfatal stroke occurred in 569 of 8,803 semaglutide participants (6.5%) and 701 of 8,801 placebo participants (8.0%). The hazard ratio was 0.80 (95% confidence interval 0.72–0.90), supporting a reduction in the combined outcome in that population.

TRIUMPH-1 measured weight and separate knee-pain and sleep-apnea outcomes. Those measurements do not establish whether retatrutide prevents cardiovascular events better than semaglutide. The relevant comparison is between measured clinical outcomes in appropriate trials, not between numbers of receptor targets.

Pharmacokinetics: persistence in the bloodstream

Urva and colleagues measured retatrutide, then called LY3437943, after injections under the skin in adults with type 2 diabetes and reported an approximate six-day elimination half-life. The current Wegovy label reports an approximate one-week elimination half-life for semaglutide. A half-life describes how long blood concentration takes to fall by half during elimination. Similar values do not establish equal appetite effects, glucose lowering or weight loss.

Semaglutide tablets and injections also differ in absorption. This article’s STEP 1 and SELECT results concern the weekly 2.4-mg injection. The June 2026 Wegovy label also includes other formulations and strengths, including tablets and the 7.2-mg injection; their existence does not turn a 2.4-mg trial result into a comparison with every current semaglutide product.

What the safety evidence can compare

Retatrutide trials commonly reported stomach and intestinal adverse events. The earlier 338-person phase 2 obesity trial found these events increased with dose and reported pulse increases that peaked at 24 weeks and declined afterward. TRIUMPH-1 also identified digestive events as the most common adverse events. Different trials and incomplete head-to-head safety data prevent assigning a relative safety ranking against semaglutide.

Semaglutide’s approved label provides a broader product-specific safety framework, including nausea, vomiting and diarrhea, pancreatic and gallbladder warnings, kidney injury associated with fluid loss, and particular risks with other medicines. It carries a boxed warning about thyroid C-cell tumors observed in rodents; whether this applies to humans remains unknown. Contraindications include a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2. Retatrutide’s investigational status leaves its final regulatory benefit-risk assessment unsettled.

Frequently asked questions

Has a trial directly compared retatrutide with semaglutide?

TRANSCEND-T2D-2 is a registered direct diabetes comparison, described by Lilly in adults taking metformin with or without an SGLT2 inhibitor. No outcome report from that trial was located for this October 15, 2026 review. The obesity percentages discussed here come from separate placebo-controlled studies.

Why can different analyses quote different weight-loss percentages?

Different analyses can estimate different quantities. This article uses the published TRIUMPH-1 main weight analysis, which accounts for treatment stopping and gives 25.0% in the 12-mg group. An estimate assuming continued treatment must be identified separately; it cannot replace the main result without explanation.

Is STEP 1 a comparison with every current semaglutide product?

STEP 1 used weekly semaglutide 2.4-mg injections. The current Wegovy label also includes other strengths and tablets. Outcomes from a particular trial remain tied to its studied formulation, dose and population.

Does greater weight loss necessarily mean better cardiovascular protection?

Weight change and cardiovascular events are different measurements. SELECT directly showed fewer combined cardiovascular deaths, nonfatal heart attacks and nonfatal strokes with semaglutide than placebo in adults with established cardiovascular disease and excess weight. The retatrutide obesity result does not establish a better cardiovascular outcome than semaglutide.

Is retatrutide approved?

The dated September 2026 Lilly report identifies retatrutide as investigational. Semaglutide has approved products with product-specific indications and warnings. Published phase 3 results and regulatory approval are separate milestones.

Retatrutide — full profile · Selected studies

Semaglutide — full profile · Selected studies

Compare other compounds · Explore the guide previews

References

  1. Jastreboff AM, Kaplan LM, Davies MJ, Wilding JPH, Ahmad NN, Murray M, Du Y, Makarova N, Giblin K, Schloot NC, Wang Y, TRIUMPH-1 Investigators. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. The New England journal of medicine. 2026. doi:10.1056/NEJMoa2604169. PMID:42814954.

    Original indexed PubMed and NEJM abstract freshly read October 15, 2026. Full report/supplements not acquired; apparent sleep-apnea subgroup sign inconsistency excluded. Abstract Methods/Results, treatment-regimen weight analysis: n=2339, 80 weeks; higher doses 23.7/25.0% versus 3.9%.

  2. Wilding JPH, Batterham RL, Calanna S, Davies M, Van Gaal LF, Lingvay I, McGowan BM, Rosenstock J, Tran MTD, Wadden TA, Wharton S, Yokote K, Zeuthen N, Kushner RF, STEP 1 Study Group. Once-Weekly Semaglutide in Adults with Overweight or Obesity. The New England journal of medicine. 2021;384(11):989–1002. doi:10.1056/NEJMoa2032183. PMID:33567185.

    Original indexed PubMed abstract and NEJM methods/results freshly retrieved October 15, 2026; direct endpoint intermittently returned a shell. Abstract Methods/Results; treatment-policy analysis and weight difference with95%CI.

  3. Lincoff AM, Brown-Frandsen K, Colhoun HM, Deanfield J, Emerson SS, Esbjerg S, Hardt-Lindberg S, Hovingh GK, Kahn SE, Kushner RF, Lingvay I, Oral TK, Michelsen MM, Plutzky J, Tornøe CW, Ryan DH, SELECT Trial Investigators. Semaglutide and Cardiovascular Outcomes in Obesity without Diabetes. The New England journal of medicine. 2023;389(24):2221–2232. doi:10.1056/NEJMoa2307563. PMID:37952131.

    Original PubMed record and indexed primary NEJM Results/Table2 freshly retrieved October 15, 2026. Abstract and Results/Table2:17604randomized,569/8803versus701/8801,HR0.80(95%CI0.72–0.90),mean follow-up39.8months.

  4. Urva S, Coskun T, Loh MT, Du Y, Thomas MK, Gurbuz S, Haupt A, Benson CT, Hernandez-Illas M, D'Alessio DA, Milicevic Z. LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes: a phase 1b, multicentre, double-blind, placebo-controlled, randomised, multiple-ascending dose trial. Lancet (London, England). 2022;400(10366):1869–1881. doi:10.1016/S0140-6736(22)02033-5. PMID:36354040.

    Original indexed primary PubMed and ScienceDirect abstract freshly retrieved October 15, 2026; complete serial PK table not acquired. Abstract Findings:LY3437943half-life approximately6days; population/route in Methods.

  5. Jastreboff AM, Kaplan LM, Frías JP, Wu Q, Du Y, Gurbuz S, Coskun T, Haupt A, Milicevic Z, Hartman ML, Retatrutide Phase 2 Obesity Trial Investigators. Triple-Hormone-Receptor Agonist Retatrutide for Obesity – A Phase 2 Trial. The New England journal of medicine. 2023;389(6):514–526. doi:10.1056/NEJMoa2301972. PMID:37366315.

    Original PubMed abstract freshly retrieved October 15, 2026; full safety tables not acquired. Abstract Results:338randomized,48weeks,gastrointestinal events and time course of heart-rate change.

  6. Novo Nordisk. WEGOVY (semaglutide) injection and tablets: U.S. prescribing information. Revised June 2026. DailyMed.

    Complete original official source freshly read October 15, 2026. Sections1–5,11–12.3and14; June2026revision.

  7. Eli Lilly and Company. Effect of Retatrutide Compared With Semaglutide in Adult Participants With Type 2 Diabetes and Inadequate Glycemic Control With Metformin With or Without SGLT2 Inhibitor (TRANSCEND-T2D-2). Trial information page. Accessed October 15, 2026.

    Complete public sponsor trial page freshly read October15,2026; no results report identified in targeted primary/official searches. Study purpose and population; comparison with semaglutide.

  8. Eli Lilly and Company. Lilly’s triple agonist, retatrutide, delivered substantial weight loss and A1C reduction, underscoring its potential promise for people with obesity and type 2 diabetes. Sponsor results release. September 29, 2026.

    Original official indexed sponsor release freshly retrieved October15,2026; used for dated status, not new efficacy percentages. Opening description of investigational status and clinical-development setting.