On September 29, the New England Journal of Medicine published TRIUMPH-1 — the pivotal Phase 3 trial for retatrutide, Eli Lilly’s triple-agonist obesity drug. The numbers are the largest ever recorded for a weight-loss medication.

What it is

Retatrutide (developed as LY3437943) hits three receptors at once: GIP, GLP-1, and glucagon. Semaglutide hits one. Tirzepatide hits two. The glucagon piece is the new idea — it’s thought to raise energy expenditure and pull fat out of the liver, on top of the appetite suppression from the other two.

What the trial showed

2,339 adults with obesity, 80 weeks. The highest-dose group lost an average of 25% of their body weight, versus under 4% on placebo. Earlier topline readouts put it at 28.3%, and in the extension for patients with severe obesity, losses reached 30% — roughly what gastric bypass surgery produces. This is the first drug to put up surgery-adjacent numbers in a randomized trial.

The supporting trials line up: 20.8% in patients with type 2 diabetes (with major blood-sugar improvement), 22.6% in patients with cardiovascular disease, 28.7% in a knee osteoarthritis trial. Liver fat dropped by more than 80% in a substudy.

The honest caveats

This is not a free lunch. Gastrointestinal side effects were the most common problem and got worse at higher doses — roughly 1 in 9 people on the top dose quit the trial over side effects. And the drug is not FDA approved. Lilly says it will file for approval in early 2027, which puts real availability in 2027-2028 at the earliest.

Honest grade: A-

The data is the strongest the field has ever produced — replicated across multiple large trials, published in top journals. The minus is for tolerability and the fact that you still can’t legally get it. Anyone selling it to you today is selling you a gray-market vial, not the drug in these trials.

Read the trial before you buy the vial.

Get the full Phase 3 findings report (free PDF)