TRIUMPH-5 Retatrutide vs Tirzepatide Trial: Design, Doses and When Results Are Due

If you searched for TRIUMPH 5 retatrutide results, they aren't out yet. TRIUMPH-5 (NCT06662383) is Lilly's double-blind trial of retatrutide against tirzepatide (Zepbound, Mounjaro) in about 800 adults with obesity, and its main result is weight change at week 80. ClinicalTrials.gov estimates primary completion in November 2026, and as of October 31, 2026 Lilly hadn't released a topline.

Every retatrutide vs tirzepatide comparison so far sets two separate trials side by side. TRIUMPH-5 is built to replace them, so this page sticks to it. For the drugs compared on side effects, dosing and price, see retatrutide vs tirzepatide; for the six trials that have reported, see retatrutide Phase 3 results.

What TRIUMPH-5 is testing

Two groups, one question: does retatrutide take off more weight than tirzepatide when each is pushed as high as a person can tolerate? Unless a row says otherwise, the details come from the ClinicalTrials.gov record, last updated July 20, 2026 and checked on October 31, 2026.

The registry's exclusion list doesn't mention diabetes. Lilly Medical Information (last reviewed April 21, 2026) and Lilly's October 28, 2026 release both describe the people as adults with obesity "with or without type 2 diabetes", but Lilly hasn't said what share have it. That share could pull the averages down: in TRIUMPH-2 (The Lancet, 2026), people with type 2 diabetes lost 18.8% on retatrutide 12 mg, against 25.0% in TRIUMPH-1's people without it (NEJM, 2026), both counted on the treatment-regimen method over 80 weeks.

The blinding matters too. TRANSCEND-T2D-2, retatrutide's head-to-head with Ozempic, was open-label, and so was SURMOUNT-5, Lilly's tirzepatide vs semaglutide trial (NEJM, 2025). In TRIUMPH-5 neither participants nor investigators know who got which drug, so expectations can't color the side-effect reports.

Which doses does TRIUMPH-5 compare?

Each drug's maximum tolerated dose, and Lilly hasn't published the milligram levels. The ClinicalTrials.gov arms say only "retatrutide" and "tirzepatide". The trial's entry in the EU Clinical Trials Information System (2024-511450-49-00) gives the main objective as: "To demonstrate that retatrutide MTD is superior to tirzepatide MTD for change in body weight." MTD is the maximum tolerated dose, the highest step each person can stay on.

Lilly has used this design before. In SURMOUNT-5, people got tirzepatide at 10 mg or 15 mg, or semaglutide at 1.7 mg or 2.4 mg, whichever was the highest they tolerated. In TRIUMPH-1's 104-week extension, retatrutide's maximum tolerated dose meant 9 or 12 mg (Lilly's May 2026 release). Those are other trials, and TRIUMPH-5's protocol could set different options.

A design like this is closer to how doctors prescribe, since they hold or lower a dose when side effects bite. The trade-off: the result won't tell you how retatrutide 12 mg compares with tirzepatide 15 mg. If TRIUMPH-5 uses the schedules from earlier trials, the climb takes 16 weeks to reach retatrutide 12 mg (2 mg, then 4, 6 and 9 mg, 4 weeks each, per TRIUMPH-1) and 20 weeks to reach tirzepatide 15 mg (2.5 mg steps every 4 weeks, per the Zepbound label and SURMOUNT-1).

Why a head-to-head trial matters here

Lilly makes both drugs, so TRIUMPH-5 is a company testing its next obesity drug against its current one. Tirzepatide is approved and sold as Zepbound and Mounjaro. Retatrutide has no approved version anywhere yet.

Placebo trials show a drug works. They can't tell a doctor which of two drugs to pick, and lining up separate trials only goes so far. TRIUMPH-1 enrolled people averaging 112.7 kg with a BMI of 40.0 and ran 80 weeks; SURMOUNT-1 averaged 104.8 kg with a BMI of 38.0 and ran 72. Randomizing people between the two drugs in one trial takes those differences out.

The trial isn't what an application waits on. On August 5, 2026, Lilly said its clinical data package was complete to support registrations for obesity, sleep apnea and knee osteoarthritis pain (Q2 2026 results, SEC filing). Lilly last said, on September 29, 2026, that it plans to submit retatrutide to the FDA in the first quarter of 2027 as a Biologics License Application (BLA). On October 2, 2026, the FDA decided that retatrutide is a drug, not a biological product, so an application would need to be filed under section 505 of the Federal Food, Drug, and Cosmetic Act. Lilly's appeal on that question is pending in the Seventh Circuit, and we found no ruling as of October 31, 2026. Our retatrutide release date page tracks the rest.

What separate trials suggest (not head to head)

Retatrutide's best obesity data comes from TRIUMPH-1, 2,339 adults without diabetes treated for 80 weeks. On Lilly's efficacy estimand, which asks what happens if everyone stays on the drug, the 12 mg group lost an average of 28.3%.

Tirzepatide's matching trial is SURMOUNT-1 (NEJM, 2022): 2,539 adults without diabetes over 72 weeks. Here are both on the treatment-regimen estimand, which counts everyone randomized, including people who stopped their shots.

Sources: Lilly's May 2026 TRIUMPH-1 release and the NEJM paper; the SURMOUNT-1 NEJM abstract.

On the efficacy estimand the top-dose gap widens to 5.8 points, because Lilly's June 2022 SURMOUNT-1 release put tirzepatide 15 mg at 22.5% on that method. So the separate trials point to a lead of about 3 to 6 points for retatrutide, which also had 8 more weeks to work. The dropout row runs the other way: about 1 in 9 people on retatrutide 12 mg (11.3%) quit over side effects, against 6.2% on tirzepatide 15 mg.

SURMOUNT-5 shows what tirzepatide does in a maximum-tolerated-dose trial. Among 751 adults with obesity and no diabetes, it took off 20.2% at 72 weeks against 13.7% for semaglutide, a gap of 6.5 points (least-squares means from the NEJM abstract).

Our read: tirzepatide has now landed near 20% in two separate trials, so expect something close to that again in TRIUMPH-5, a bit lower if many participants have diabetes. Retatrutide would need to land about 3 to 6 points higher to match the separate-trial gap.

What would count as a meaningful win

Passing the main test is the easy part. In SURMOUNT-5, each drug's 95% confidence interval was 2.3 points wide with 751 people. TRIUMPH-5 is about the same size, so by our estimate a gap of 2 points would probably be enough to show superiority on paper. Beyond the pass, here's how to read the size of the lead:

The weight number is only half the readout. On the day, check:

1. Which estimand each figure uses. Lilly's TRANSCEND-T2D-2 release gave efficacy-estimand numbers only, and those run higher than treatment-regimen numbers.
2. How many people stopped each drug because of side effects.
3. Nausea, vomiting and burning or oversensitive skin (dysesthesia). In TRIUMPH-1, 12.5% of people on 12 mg had dysesthesia, against 0.9% on placebo.
4. The doses people actually reached on each drug, if Lilly reports them.
5. Waist, blood pressure, cholesterol, A1C and quality of life, the registry's secondary results.

Our read: the dropout gap matters about as much as the weight gap, because weight only comes off on a drug you can keep taking. A 4-point lead with twice as many people quitting over side effects is a different choice for a patient than the same lead with similar quitting.

TRIUMPH 5 retatrutide results

Not released as of October 31, 2026. Lilly hasn't issued a TRIUMPH-5 release, its third-quarter 2026 results (October 29) don't mention a topline, and ClinicalTrials.gov has no posted results. Lilly's October 28, 2026 release still lists the trial as ongoing.

When to expect them: ClinicalTrials.gov estimates primary completion in November 2026 and study completion in December 2026, and the EU register gives an estimated end date of November 16, 2026. Lilly hasn't announced a date. Its past toplines came 27 to 98 days after primary completion, by our count from registry and release dates, which points to about late November 2026 to early March 2027.

What TRIUMPH-5 won't answer

Even a clean win leaves some questions open:

• Muscle. The registry lists no body-composition scan, so the trial won't show how much of the weight lost on each drug was fat.
• Heart and kidney outcomes. None is a TRIUMPH-5 endpoint. TRIUMPH-Outcomes, about 10,000 people, has an estimated primary completion of February 2029.
• Switching. Anyone on a weight-loss drug in the 90 days before screening was excluded, so the trial says nothing about moving from tirzepatide to retatrutide. Our page on switching from tirzepatide covers what is known.
• Life after week 80. The registry lists no extension.

A positive readout doesn't change what you can legally buy. Lilly says retatrutide "cannot be legally sold or marketed for human use", so anything listed online as retatrutide for sale isn't Lilly's product or the drug these trials tested.

TRIUMPH-5 is closed to new people. As of October 31, 2026 the only Lilly retatrutide study recruiting on ClinicalTrials.gov is SYNERGY-Outcomes, a liver-disease trial; upcoming retatrutide trials lists what's still running.