The short version
Retatrutide is the "triple agonist" everyone keeps asking about. It hits three hormone receptors at once: GIP, GLP-1 and glucagon.
In 2023, its phase 2 trial made headlines with an average weight loss of 24.2% at 48 weeks on the highest dose (Jastreboff et al., NEJM 2023).
The big question was whether phase 3, the large trials regulators rely on, would hold up. So far, Eli Lilly says it has. Here is the scorecard.
The TRIUMPH scorecard
TRIUMPH-4 (announced December 11, 2025): adults with obesity and knee osteoarthritis. On the highest dose, average weight loss was 28.7% at 68 weeks, and knee pain scores dropped sharply compared with placebo.
TRIUMPH-1 (announced May 21, 2026): the main obesity trial, with 2,339 adults. Average weight loss was 28.3% at 80 weeks on the highest dose, versus 2.2% on placebo. In a pre-planned extension for people starting at a BMI of 35 or more, the highest-dose group reached 30.3% at 104 weeks.
TRIUMPH-2 and TRIUMPH-3 (announced July 23, 2026): adults with type 2 diabetes lost up to 20.8% on average at 80 weeks, with A1C down by up to 1.6 points. Adults with severe obesity and existing heart disease lost up to 22.6%.
Then came the peer-reviewed papers. On September 29, 2026, the full TRIUMPH-1 results appeared in the New England Journal of Medicine and the full TRIUMPH-2 results appeared in The Lancet.
What comes next
Lilly says it plans to ask the FDA for approval in the first quarter of 2027.
The matchup everyone wants is TRIUMPH-5, a head-to-head trial of retatrutide versus tirzepatide. Its registry listing shows primary completion expected around November 2026. Until those results are out, any claim that retatrutide "beats" tirzepatide is a guess built on comparing different trials.
Liver fat is another one to watch. A small phase 2 substudy (Sanyal et al., Nature Medicine 2024) found most participants on the higher doses reached normal liver-fat levels, but phase 3 liver results have not been reported yet.
The fine print
Different headlines use different math. Lilly's press releases lead with the "efficacy estimand" (as if everyone stayed on the drug). The journal papers lead with the "treatment-regimen estimand" (everyone randomized, whether or not they stayed on it), which gives lower numbers, for example 25.0% versus 3.9% on placebo in TRIUMPH-1.
Side effects were mostly gastrointestinal: nausea, diarrhea, constipation and vomiting, more often at higher doses. An unusual skin sensation called dysesthesia was also reported more often than on placebo. More people quit for side effects on the higher doses.
Retatrutide is not approved anywhere. Lilly says it is investigational and cannot be legally sold or marketed for human use, so anything sold online as retatrutide is not the product tested in these trials.
This is education, not medical advice. If weight or metabolic health is on your mind, talk with a licensed clinician who knows your history.
Want the plain-English rundown on retatrutide and the other peptides everyone is talking about? Grab The Peptide Playbook, our free guide, at /guide.
