Retatrutide
Retatrutide, often called "reta", is Eli Lilly's experimental weekly injection. Its Phase 3 results are among the strongest reported for any weight-loss drug. It is not approved, and it cannot be legally sold for human use.
- Legal lane: investigational. No legal access outside a clinical trial.
- Evidence grade: B
- Form: weekly injection under the skin
- FDA filing: Lilly plans to submit in the first quarter of 2027
What it is
Retatrutide is a single molecule that activates three hormone receptors: GIP, GLP-1 and glucagon. Semaglutide acts on one of these and tirzepatide on two.
What the evidence shows
Lilly reported two pivotal Phase 3 trials in July 2026, each lasting 80 weeks.
| Trial | Who was studied | Average weight loss |
|---|---|---|
| TRIUMPH-2 | 1,152 adults with obesity or overweight and type 2 diabetes | 12.7% (4 mg), 19.1% (9 mg), 20.8% (12 mg) |
| TRIUMPH-3 | 1,949 adults with severe obesity and cardiovascular disease | 21.6% (9 mg), 22.6% (12 mg), versus 3.2% on placebo |
These are topline company results. Full data had not yet been published in a peer-reviewed journal when Lilly announced them, which is why this page grades the evidence B and not A. The grade will change if the FDA approves it.
Dosing used in the trials
There is no approved dose. In the Phase 3 trials, participants started at 2 mg once a week and stepped up every four weeks:
- To a 9 mg target: 2 mg, 4 mg, 6 mg, then 9 mg.
- To a 12 mg target: 2 mg, 4 mg, 6 mg, 9 mg, then 12 mg.
This was done under trial monitoring with pharmaceutical-grade product. It is a description of the studies, not guidance for self-use.
Side effects
- The most common were diarrhea (up to about 34% of participants), nausea (up to 28%) and vomiting.
- About 6% of participants on retatrutide in TRIUMPH-3 reported dysesthesia, an abnormal skin sensation, compared with 1.3% on placebo.
- In TRIUMPH-3, 9.8% (9 mg) and 13.5% (12 mg) stopped treatment because of side effects, versus 4.8% on placebo.
Legal status
In Lilly's own words, retatrutide "cannot be legally sold or marketed for human use." Every vial sold online as retatrutide is an unapproved product from an unverified source. The FDA has sent warning letters to sellers, and Lilly sued six of them in August 2026. See the tracker.
Sources
- Eli Lilly: TRIUMPH-2 and TRIUMPH-3 topline results, July 23, 2026
- HCPLive: retatrutide Phase 3 summary
- VialAudit: FDA letters and Lilly lawsuits
This compound appears in widely promoted weight-loss stacks alongside the others. No trial has tested those combinations; see blends and stacks.