Updated October 31, 2026

Retatrutide, explained.

Eli Lilly's once-weekly GIP, GLP-1 and glucagon triple agonist, in plain English. Dosing, results, side effects and every trial, with each number linked to the study it came from.

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Sourced to the published trials
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A retatrutide vial and syringe with three rings, one for each receptor it activates

28.3%

average weight loss on 12 mg at 80 weeks in TRIUMPH-1

Investigational · US filing planned Q1 2027

Phase 3 trials reported, as of Oct 31, 2026: 6
people randomized across them (our sum of Lilly's per-trial figures): 7,720
weight lost on 12 mg vs Ozempic 2 mg in TRANSCEND-T2D-2: 20.9% vs 9.4%
Lilly's planned US filing, as it last said on Sep 29, 2026: Q1 2027

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Dosage

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Trial doses week by week, units and vials

Side effects

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What is common, what is rare, what helps

Compare

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Against tirzepatide, Ozempic and the rest

Conditions

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Diabetes, liver, sleep apnea, knees

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Price, legality and checking a vial

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Units, mixing, drug levels and trial timelines, worked out from the published numbers.

Dose to syringe units

U-100 syringe

Vial

BAC water (mL)Dose (mg)

40units0.40 mL at 5 mg/mL

5 doses per vial at this doseOpen the full calculator

Retatrutide in 60 seconds

Retatrutide is an experimental once-weekly injection from Eli Lilly and Company for obesity and type 2 diabetes. It's a single peptide that switches on three hormone receptors at once (GIP, GLP-1 and glucagon), which is why it gets called a triple agonist, and online "reta" or "GLP-3". As of October 31, 2026, six Phase 3 trials have reported positive results, and no approved version exists yet anywhere in the world.

The headline numbers come from two of those trials. In TRIUMPH-1, adults without diabetes on the top 12 mg dose lost an average of 28.3% of their body weight over 80 weeks. In TRANSCEND-T2D-2, the first head-to-head trial, people with type 2 diabetes lost 20.9% on 12 mg against 9.4% on Ozempic 2 mg. Lilly has said it plans to file in early 2027, but on October 2 the FDA decided what kind of application it needs, and Lilly's appeal on that question is pending in court.

Retatrutide acts on GIP, GLP-1 and glucagon receptors. Tirzepatide acts on the first two, semaglutide only on GLP-1.
Average weight loss on 12 mg ran from 16.8% at 40 weeks in type 2 diabetes to 28.7% at 68 weeks in knee osteoarthritis (efficacy estimand).
In all six Phase 3 trials, more people stopped because of side effects on 12 mg than on placebo or Ozempic.
No approved version exists anywhere, and when Australia's regulator tested a vial sold as retatrutide, it held none.

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