Retatrutide TRIUMPH-1 Results: Up to 30% Weight Loss in Phase 3

On May 21, 2026, Eli Lilly shared topline results from TRIUMPH-1. This was a Phase 3 trial of retatrutide in adults with obesity or overweight who did not have diabetes. Phase 3 is the last big testing step before a company asks regulators for approval.

Retatrutide is a once-weekly shot. It works on three body signals at once: GIP, GLP-1, and glucagon. Drugs like Wegovy and Zepbound hit one or two of these. Retatrutide is the first in its class to also act on glucagon, which is one reason people watch it so closely.

The trial enrolled 2,339 people and ran for 80 weeks, with a smaller group continuing to 104 weeks. Lilly says it met its main goals at every dose. The results are topline only, which means the full data has not been published in a medical journal yet.

People started the trial at an average weight of about 248 lbs. Here is how much weight each dose took off at 80 weeks, compared to a placebo (a fake shot with no drug).

A smaller group with higher starting weight kept going to 104 weeks, which is two years. In that group, the 12 mg dose reached 30.3% average weight loss, or about 85 lbs. Lilly's investigators noted that 30% weight loss has long been a level usually seen only with weight-loss surgery.

One number stands out for context. At 80 weeks, 65.3% of people on 12 mg dropped to a BMI under 30, which is the line that defines obesity. The 4 mg dose is also worth noting: it reached about 19% weight loss with just one dose-increase step, which may matter for people who do not tolerate higher doses.

The side effects looked similar to other GLP-1-class drugs. Most were stomach-related and showed up more often at higher doses. Lilly reported the following as the most common, listed for 12 mg versus placebo.

Two less common effects stood out. Dysesthesia, which is an odd skin sensation like tingling or burning, hit 12.5% on 12 mg versus 0.9% on placebo. Urinary tract infections were also a bit higher. Lilly said most of these were mild to moderate and many cleared up while people kept taking the drug.

Dropouts matter too. About 11.3% of people on 12 mg stopped because of side effects, compared to 4.9% on placebo. At the lower 4 mg dose, the dropout rate was actually close to placebo. That trade-off between bigger results and more side effects is the real story at the top dose.

Lilly already sells two big obesity drugs: Zepbound (tirzepatide), a weekly shot, and Foundayo (orforglipron), a daily pill. Retatrutide would sit at the high end of weight loss if it gets approved. These are different drugs and are not interchangeable.

The headline gap is the third target. By also acting on glucagon, retatrutide may push weight loss higher than the two-target drugs. Lilly framed it as a way to match the drug to the person, with the 4 mg dose for milder needs and 12 mg for the largest weight loss.

If you research peptides, you have probably seen "retatrutide" sold by research-use suppliers. It is important to be clear: that is not the same thing as the Lilly drug studied in TRIUMPH-1.

Lilly's retatrutide is an investigational medicine. As of May 2026, it is legally available only to people enrolled in Lilly's clinical trials. There is no approved brand, no pharmacy version, and no FDA-cleared dose for the public. The TRIUMPH-1 numbers come from that controlled trial, with a known molecule, a known dose, and medical monitoring.

Research-use compounds sold under the same name are a separate market with no FDA approval and no guarantee of identity, purity, or dose. The trial results do not transfer to those products. If you read about research-use peptides, treat purity testing and documentation as the first question, not the last.

Topline Phase 3 data is a milestone, not an approval. The usual path is: finish the trials, submit the full data to the FDA, wait for review, then a possible launch. That process takes time and is never guaranteed.

Lilly said more Phase 3 data is coming later in 2026, including TRIUMPH-2 (people with type 2 diabetes) and TRIUMPH-3 (people with heart disease). Some TRIUMPH-1 details are set to be presented at the American Diabetes Association meeting in 2026. Watch those readouts for the fuller picture.

For now, the honest answer is that there is no public way to get the Lilly drug outside a trial. If you want the access angle, see our existing explainer linked below, but the regulatory reality has not changed with this announcement.

TRIUMPH-1 is one of the strongest obesity-drug results reported so far, with up to 30% average weight loss in a two-year subgroup. The side-effect and dropout numbers at the top dose are the trade-off to keep in view.

It is still investigational, still topline-only, and still trial-only as of May 2026. The result is a big deal for the field. It is not a reason to treat research-use "retatrutide" as a proven product.