Tirzepatide vs retatrutide
Tirzepatide acts on two receptors (GIP and GLP-1) and is FDA-approved. Retatrutide adds a third, glucagon, and is not approved. In separate trials, top-dose weight change was −20.9% at 72 weeks on tirzepatide 15 mg (SURMOUNT-1) and −25.0% at 80 weeks on retatrutide 12 mg (TRIUMPH-1). No head-to-head trial exists.[1,2]
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At a glance
How do Tirzepatide and Retatrutide compare?
No published trial has compared these directly. The numbers come from separate trials with different people and lengths, so treat the gap between them as a rough guide, not a measured difference.
| Tirzepatide | Retatrutide | |
|---|---|---|
| Receptors | TirzepatideGIP and GLP-1 | RetatrutideGIP, GLP-1 and glucagon |
| FDA status[3,2] | TirzepatideApproved: Mounjaro (2022), Zepbound (2023) | RetatrutideNot approved for any use |
| Developer | TirzepatideEli Lilly | RetatrutideEli Lilly |
| How often | TirzepatideOnce a week | RetatrutideOnce a week |
| Main obesity trial[1,2] | TirzepatideSURMOUNT-1: 2,539 adults, 72 weeks | RetatrutideTRIUMPH-1: 2,339 adults, 80 weeks |
| Weight change on the top dose, with timeframe[1,2] | Tirzepatide−20.9% on 15 mg at 72 weeks (placebo −3.1%) | Retatrutide−25.0% on 12 mg at 80 weeks (placebo −3.9%) |
| Weekly doses used in the phase 3 trials[1,2,4] | Tirzepatide5, 10 and 15 mg (SURMOUNT-1) | Retatrutide4, 9 and 12 mg (TRIUMPH-1 and -2) |
| Weekly doses used in the phase 2 trial[5] | TirzepatideNot covered here (label doses are on the tirzepatide dosage chart) | Retatrutide1, 4, 8 and 12 mg over 48 weeks |
| Stopped because of side effects[1,4] | TirzepatideSURMOUNT-1: 4.3% to 7.1% (placebo 2.6%) | RetatrutideTRIUMPH-2: 4% to 12% (placebo 5%) |
| Side effects beyond the stomach[3,4] | TirzepatideBoxed warning about thyroid C-cell tumours seen in rodents | RetatrutideLow blood pressure and dysesthesia (unusual skin sensations), more common at higher doses |
Receptors
Which receptors does each one act on?
Tap a drug to compare. Each extra receptor adds another hormone signal. More receptors does not by itself mean safer or better.
What is the difference between tirzepatide and retatrutide?
The number of hormone receptors and the approval status. Tirzepatide activates GIP and GLP-1 receptors and is sold on prescription as Mounjaro and Zepbound. Retatrutide activates those two plus the glucagon receptor, which is thought to increase energy use and liver fat burning. Retatrutide is still investigational.[3,2]
Does retatrutide cause more weight loss than tirzepatide?
It is not known, because no trial has compared them. In separate phase 3 trials, average weight change on the top dose was −25.0% over 80 weeks for retatrutide (TRIUMPH-1) and −20.9% over 72 weeks for tirzepatide (SURMOUNT-1). Different people and trial lengths make that only a rough guide.[2,1]
How do the side effects compare?
Both mainly cause stomach and gut effects such as nausea and diarrhea. In TRIUMPH-2, retatrutide also caused more low blood pressure and unusual skin sensations (dysesthesia) than placebo, increasing with dose, and heart rate rose with dose in phase 2. Tirzepatide's label carries a boxed warning about thyroid C-cell tumours.[4,5,3]
Is retatrutide available on prescription?
No. Retatrutide is not approved by the FDA for any use, so there is no pharmacy version. Phase 3 results were published on September 29, 2026. Tirzepatide has been approved since 2022. Anything sold as retatrutide today is an unregulated research product.[2,4,3]
Work out the units for your vial
Milligrams are not comparable between compounds, and the units on your syringe depend on your vial and how much water you add. Each guide has a chart for its common vial sizes.
Questions
Common questions
Is retatrutide stronger than tirzepatide?
No trial has compared them. Top-dose results from separate trials were −25.0% (retatrutide, 80 weeks) and −20.9% (tirzepatide, 72 weeks). The trials differed in length and participants, so the gap is a rough guide only.
What does the third receptor in retatrutide do?
Retatrutide adds the glucagon receptor to the GIP and GLP-1 receptors that tirzepatide acts on. Glucagon signalling is thought to increase energy use and liver fat burning, on top of the appetite effects of the other two.
Are the doses of tirzepatide and retatrutide comparable?
No. They are different molecules. SURMOUNT-1 tested 5, 10 and 15 mg of tirzepatide weekly; the TRIUMPH trials tested 4, 9 and 12 mg of retatrutide weekly. A milligram of one is not equivalent to a milligram of the other.
Who makes tirzepatide and retatrutide?
Both come from Eli Lilly. Tirzepatide is its approved medicine (Mounjaro, Zepbound). Retatrutide, also known as LY3437943, is still in development.
Sources
- 1.Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1)
Jastreboff AM et al. N Engl J Med 2022;387:205-216 · Human trial - 2.Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1)
Jastreboff AM et al. N Engl J Med 2026 (online Sep 29) · Human trial - 3.Zepbound label
FDA. Zepbound (tirzepatide) prescribing information, 2024 · FDA - 4.Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2)
Bellido V et al. Lancet 2026 (online Sep 29) · Human trial - 5.Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial
Jastreboff AM et al. N Engl J Med 2023;389:514-526 · Human trial
Last reviewed Nov 7, 2026. Education only, not medical advice. PepDose sells no peptides.