Retatrutide's phase 3 TRIUMPH results: what they showed and what comes next

Four phase 3 trials of Eli Lilly's triple-hormone drug reported strong weight loss in 2025–2026. Here is what the numbers mean, the new side effect to know about, and the filing timeline.

Retatrutide is an experimental once-weekly injection from Eli Lilly. It acts on three hormone receptors at once: GIP, GLP-1 and glucagon. Tirzepatide (Mounjaro, Zepbound) acts on the first two, and semaglutide (Ozempic, Wegovy) acts on GLP-1 only.

Between December 2025 and September 2026, Lilly reported results from four phase 3 trials in its TRIUMPH program. This post sums up what they found, how they compare with today's approved drugs, and what has to happen before retatrutide could reach pharmacies.

The four trials so far

TRIUMPH-4 (December 2025) enrolled adults with obesity and knee osteoarthritis. At 68 weeks, people on the 12 mg dose lost an average of 28.7% of their body weight, compared with 2.1% on placebo. Knee pain scores also fell sharply.

TRIUMPH-1 (May 2026) is the main obesity trial, with 2,339 adults followed for 80 weeks. Average weight loss was 19.0% on 4 mg, 25.9% on 9 mg and 28.3% on 12 mg, compared with 2.2% on placebo. On the top dose, 45.3% of people lost at least 30% of their body weight. In an extension to 104 weeks for people who started with a BMI of 35 or higher, the 12 mg group reached an average of 30.3%. Lilly presented the full data at the American Diabetes Association meeting in June.

TRIUMPH-2 and TRIUMPH-3 (July 2026) tested harder-to-treat groups. TRIUMPH-2 enrolled 1,152 adults with type 2 diabetes. Weight loss at 80 weeks reached 20.8% on 12 mg (4.0% on placebo), and A1c, a measure of long-term blood sugar, fell by up to 1.6 points. TRIUMPH-3 enrolled 1,949 adults with severe obesity and existing heart disease. Weight loss reached 22.6% on 12 mg (3.2% on placebo). In late September, Lilly presented detailed TRIUMPH-2 results at the European diabetes meeting (EASD), and they were published in The Lancet at the same time.

People with diabetes usually lose less weight on these drugs than people without it, so a lower number in TRIUMPH-2 is expected, not a sign of failure.

How it compares with tirzepatide and semaglutide

Here are the headline results from each drug's main obesity trial:

Semaglutide 2.4 mg (STEP-1): about 15% at 68 weeks.
Tirzepatide 15 mg (SURMOUNT-1): about 21% at 72 weeks.
Retatrutide 12 mg (TRIUMPH-1): 28.3% at 80 weeks.

Be careful with this list. These were separate trials, run at different times, with different people and different lengths, so the numbers can't be compared directly. The only fair way to compare two drugs is to test them against each other in the same trial. Tirzepatide has done that against semaglutide: in SURMOUNT-5, tirzepatide gave 20.2% weight loss versus 13.7% for semaglutide over 72 weeks.

Retatrutide has not been through a published head-to-head trial yet. Lilly is running one against tirzepatide (TRIUMPH-5). Its trial registry entry estimates it will finish around November to December 2026. No results have been released.

Side effects, including a new one

As with other drugs in this class, the most common side effects were stomach and gut problems. In TRIUMPH-1, nausea affected 42.4% of people on 12 mg versus 14.8% on placebo, and vomiting 25.3% versus 4.8%. These problems were linked to the dose and were most common while the dose was being raised.

The new issue is dysesthesia: skin that feels tingly, sensitive or painful to normal touch. It showed up in all the trials. In TRIUMPH-4, 20.9% of people on 12 mg reported it, compared with 0.7% on placebo. In TRIUMPH-1 the figures were 12.5% versus 0.9%, and in TRIUMPH-2 they were 7.3% versus 0.7%. Most cases were mild to moderate, and many went away during treatment. Researchers don't yet fully understand why it happens.

More people stopped taking the drug because of side effects as the dose went up. In TRIUMPH-1, 11.3% stopped on 12 mg, compared with 4.9% on placebo. In TRIUMPH-3, the figure was 13.5% on 12 mg versus 4.8% on placebo.

Very large weight loss raises its own questions, such as loss of muscle along with fat, gallbladder problems and nutrition. Longer follow-up will matter.

What's next: the filing timeline

Lilly has said it plans to send its application for retatrutide to the FDA (a Biologics License Application) in the first quarter of 2027. A standard FDA review of a new drug often takes around a year from submission, and faster review pathways exist. Either way, there is no confirmed approval date, and an application is not a guarantee of approval. More phase 3 trials, including the head-to-head study and trials in other conditions, are still running.

Until then, retatrutide is not approved in any country. No pharmacy can legally compound it in the US, because it is not an approved drug and is not on any compounding list.

A note on "research" retatrutide

Retatrutide is already sold online as a "research chemical". These products are not the drug used in the TRIUMPH trials, and nothing checks their purity, dose or sterility. Public Citizen, a consumer group, reported in June 2026 that the FDA had sent 14 warning letters to retatrutide sellers since late 2024, and that most of those sellers kept marketing peptides afterwards. The trial results tell us about Lilly's product, given under medical supervision. They say nothing about whether an unregulated vial is safe.

You can read our full retatrutide page for how it works, its regulatory status and its warnings, and compare it with tirzepatide and semaglutide.

This is educational information, not medical advice.