What's New: September 2026 Update

• Full TRIUMPH-2 data lands September 30, at an EASD-sponsored symposium in Milan. Everything published from that trial so far is topline. We will update this page afterwards.
• Regulatory path confirmed (July 23, 2026). Lilly plans to submit a Biologics License Application to the FDA in Q1 2027 — a BLA rather than an NDA, because retatrutide is regulated as a biologic.
• A narrow pre-approval access route exists. Lilly confirmed in August 2026 that it supplies retatrutide to a limited number of patients meeting strict medical criteria. Details below.
• Nothing has changed for the approved drugs. Tirzepatide and semaglutide remain the only two that can be prescribed today.

The Short Version

Semaglutide targets one receptor, tirzepatide two, retatrutide three — and the headline weight-loss figures line up with that progression almost too neatly. They are also not measured the same way, which means the gaps between them are smaller than they look.

If semaglutide's figure looks unfamiliar, that is the point: it is the one measured the same way as the other two.

Why These Numbers Don't Line Up

Obesity trials report results two ways. The efficacy estimand — Novo Nordisk calls its version the trial product estimand — measures the effect among participants taking the drug as intended. The treatment-regimen estimand includes everyone randomised, including people who stopped early or never reached the top dose. The first number is always larger.

Retatrutide's 28.3% and tirzepatide's 22.5% are efficacy figures. Semaglutide's widely quoted 14.9% is the conservative one; its efficacy figure is 16.9%. So the usual line-up sets two optimistic numbers against one conservative number and reads the difference as pharmacology.

Measured consistently, retatrutide's advantage over semaglutide is about 67% on the as-intended basis and 68% across all participants — not the roughly 90% in circulation. Over tirzepatide it is 26% and 20%. The ordering never changes; the distance does.

The Three Trials

TRIUMPH-1 — retatrutide

2,339 adults with obesity, without type 2 diabetes. 80 weeks; 4 mg, 9 mg and 12 mg against placebo, which lost 2.2%. Topline results May 21, 2026. At 12 mg, 62.5% of participants lost at least a quarter of their body weight under the efficacy estimand.

You will more often see 28.7% quoted for retatrutide. That comes from TRIUMPH-4 — 445 adults with obesity and knee osteoarthritis, over 68 weeks. It is a real Phase 3 result, but it is a specialty population less than a fifth the size, set against two general-obesity trials of roughly 2,000 to 2,500 people. TRIUMPH-1 is the trial built for that comparison, and the difference between the two figures is four tenths of a point.

SURMOUNT-1 — tirzepatide

2,539 adults with obesity or overweight. 72 weeks; 5 mg, 10 mg and 15 mg against placebo, which lost 2.4%. At 15 mg, 63% lost at least a fifth of their body weight under the efficacy estimand, 57% under the treatment-regimen estimand.

STEP 1 — semaglutide

1,961 adults with obesity or overweight, 68 weeks at 2.4 mg. Under the treatment-policy estimand, 32.0% lost at least a fifth of their body weight, against 1.7% on placebo.

Responder rates: two of the three

On a like-for-like basis the two approved drugs compare directly. Across all participants, 57% of those on tirzepatide 15 mg lost at least a fifth of their body weight, against 32.0% on semaglutide — a gap wider than the average weight-loss figures alone suggest.

Retatrutide cannot be added to that row. Lilly published the share of TRIUMPH-1 participants losing at least 25% of body weight, not 20%, which is a different question. Setting 62.5% beside 63% would imply a dead heat nobody has measured.

Mechanism

Semaglutide acts on the GLP-1 receptor: slows gastric emptying, reduces appetite, improves insulin response. Sold as Ozempic for type 2 diabetes and Wegovy for weight management.

Tirzepatide adds GIP, which improves insulin sensitivity. It also has the lowest nausea rate of the three despite acting on two receptors rather than one, and why that is remains unsettled. Sold as Mounjaro and Zepbound.

Retatrutide adds glucagon, which raises energy expenditure and mobilises liver fat. Where the other two mainly reduce energy taken in, retatrutide also increases energy burned — the most plausible explanation for both the larger weight loss and the side effect below.

Tolerability

Tirzepatide is the best tolerated: lowest nausea, lowest discontinuation. Semaglutide has high nausea but low discontinuation, which suggests its nausea is more often manageable than disqualifying. Retatrutide's discontinuation rate at 12 mg is about 1.6 times semaglutide's and 1.8 times tirzepatide's.

Diarrhoea and vomiting are left out on purpose. Retatrutide's rates in TRIUMPH-1 were 32.0% and 25.3%, but the semaglutide figures in circulation come from a pooled analysis of STEP 1 through 3 rather than STEP 1 alone, and the tirzepatide materials do not itemise them by dose. Lining those up would compare three different things.

Dysesthesia

Dysesthesia is an altered sense of touch — tingling, burning, or ordinary contact registering as unpleasant. In TRIUMPH-1, 12.5% of participants on 12 mg reported it against 0.9% on placebo; in TRIUMPH-4, 20.9% against 0.7%. Neither comparator produces it, and the glucagon receptor is the most likely explanation.

Lilly reported that these events did not generally cause participants to stop treatment. Analysts at BMO Capital Markets noted the signal had not appeared in Phase 2 and said they would watch for it in later readouts. The full publications will say more than topline releases have.

Dosing: Two Labels and One Protocol

An approved drug has an FDA label setting the starting dose, each step, and the maximum. It exists because the FDA reviewed the evidence and decided what was safe to tell a large population to do.

An investigational drug has a protocol instead — the schedule one trial used, on a screened population, with monitoring and a clinician who could pause or lower the dose the moment something went wrong. A protocol records what happened under those conditions. It is not instructions, and it does not transfer to someone using a vial bought online.

Semaglutide (Wegovy), from the label: Week 1–4: 0.25 mg → Week 5–8: 0.5 mg → Week 9–12: 1 mg → Week 13–16: 1.7 mg → Week 17 onward: 2.4 mg

Tirzepatide (Zepbound), from the label: Week 1–4: 2.5 mg → Week 5–8: 5 mg → Week 9–12: 10 mg → Week 13 onward: 15 mg

Retatrutide: no label, no approved dose. The Phase 3 programme studied maintenance doses of 4 mg, 9 mg and 12 mg under trial supervision. There is no approved starting dose and no approved maximum until the FDA reviews Lilly's filing and a label is published.

This matters for the tolerability figures too. Retatrutide's discontinuation rate comes from trials where escalation was fixed by protocol. Whether it is better tolerated when a prescriber can slow a titration down is one of the things a label will settle.

Availability

Semaglutide — Ozempic approved for type 2 diabetes in 2017, Wegovy for weight management in June 2021. About five years of post-marketing data in the weight-management indication, and longer as a diabetes drug.

Tirzepatide — Mounjaro approved for type 2 diabetes in May 2022, Zepbound for weight management in November 2023.

Retatrutide — not approved by the FDA or any other regulator, for any use. It cannot lawfully be prescribed, sold or dispensed. Lilly plans to file in Q1 2027; what follows a filing is a review, not a decision date. The FDA can accept or refuse to file, request more data, or approve with restrictions. Anyone quoting a launch date is estimating.

The one pre-approval route. In August 2026 Lilly confirmed it supplies retatrutide to a small number of patients outside clinical trials. A patient must be 18 or older, have treatment-resistant obesity, have at least two serious or life-threatening obesity-related complications, and be unable to enrol in a trial or access a comparable treatment. A Lilly spokesperson said: "For a limited number of patients who meet specific medical criteria and cannot enroll in a clinical trial, we believe it is medically appropriate to make authentic retatrutide available before FDA approval, consistent with FDA's guidance."

That is a route through a treating physician for people with advanced disease. It is not a purchase, and it is not open to people who simply want the drug early.

It also draws a line worth stating plainly. Lilly's own word is authentic. Vials sold online as "retatrutide" — by peptide sellers, research-chemical sites or compounding operations — are not that product. They are not made under pharmaceutical manufacturing oversight, their contents are not verified, and nobody is monitoring the person taking them. Every figure in this article describes Lilly's molecule under trial conditions. None of them describe anything bought from a website.

Cost

List prices mean little in 2026. Both manufacturers sell directly at a fraction of list, and the Medicare GLP-1 Bridge demonstration — running July 1, 2026 through December 31, 2027 — puts eligible beneficiaries at $50 a month. Commercial coverage for weight management remains inconsistent and many plans exclude it, while coverage for type 2 diabetes is routine with prior authorisation.

What the Data Supports

Tirzepatide has the stronger numbers among drugs that can be prescribed: more weight loss than semaglutide under either estimand, the lowest nausea rate of the three, and the lowest discontinuation rate at 6.2%. Nearly three years of post-marketing data in the weight-management indication, and longer as a diabetes drug.

Semaglutide has the longest record in weight management — about five years — and a 7.0% discontinuation rate. Its efficacy is the lowest of the three, though by less than the usual figures suggest. Its high nausea rate appears to be the more tolerable kind, judging by how few people stopped because of it.

Retatrutide produced the most weight loss and is the only one that also raises energy expenditure. It is also the least tolerable, and it cannot be prescribed. The question is not whether the trial numbers are better — they are — but what weight numbers for an unavailable drug should carry in a decision made now.

Which of these matters most depends on things this article cannot know: what you have already tried, what you tolerated, what your insurance covers, and what else is going on with your health. That is a conversation for a prescriber.

Conclusion

The efficacy gradient is real — 16.9%, 22.5%, 28.3% among participants taking each drug as intended; 14.9%, 20.9% and 25.0% across all participants. What the usual comparison overstates is the distance, because it sets an as-intended number against an all-participants one.

The gradient runs the other way too. Retatrutide's discontinuation rate is 1.6 to 1.8 times either approved drug's, and it produces a sensory side effect in one in eight participants at 12 mg in TRIUMPH-1 — one in five in TRIUMPH-4 — that neither comparator causes.

Two of these drugs can be prescribed today. The third is a filing away from a review that has not started. We will update this page after the full TRIUMPH-2 results are presented at EASD on September 30.

Sources

• Eli Lilly. Retatrutide delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1). May 21, 2026.
• Eli Lilly. Retatrutide successful in two additional Phase 3 obesity trials (TRIUMPH-2, TRIUMPH-3). July 23, 2026.
• Eli Lilly. Retatrutide delivered weight loss of up to an average of 71.2 lbs (TRIUMPH-4). December 11, 2025.
• Eli Lilly. SURMOUNT-1 results published in The New England Journal of Medicine. 2022. (Both estimands.)
• Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity. N Engl J Med. 2022;387(3):205–216.
• Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989–1002.
• Wharton S, Calanna S, Davies M, et al. Gastrointestinal tolerability of once-weekly semaglutide 2.4 mg. Diabetes Obes Metab. 2022;24(1):94–105.
• Eli Lilly. Lilly to present new data on Foundayo, retatrutide, and eloraTZP at EASD 2026. September 2026.
• Eli Lilly statement on pre-approval access to retatrutide, reported August 2026.
• BioSpace. Lilly's retatrutide scores triple trial triumph, but new safety signal emerges. 2026. (BMO Capital Markets commentary on dysesthesia.)
• Centers for Medicare & Medicaid Services. Medicare GLP-1 Bridge: GLP-1 Drugs for $50 a Month. 2026.
• U.S. Food and Drug Administration. Approval records for Ozempic (2017), Wegovy (June 2021), Mounjaro (May 2022) and Zepbound (November 2023).

Medical Disclaimer: This article is for informational purposes only and is not medical advice. Retatrutide is investigational and not approved by the FDA for any use. Semaglutide and tirzepatide are prescription medications. Nothing here is a recommendation to use, seek out or avoid any medication. Consult a qualified healthcare provider about your own treatment. Individual results vary.