Not a head-to-head comparisonThe numbers below come from separate trials with different lengths and populations. They give context, not a direct comparison. The head-to-head trial, TRIUMPH-5, has no results yet.
At a glance
| Retatrutide | Tirzepatide | |
|---|---|---|
| Receptors | GIP, GLP-1, glucagon | GIP, GLP-1 |
| Status | Investigational | FDA-approved (Zepbound, Mounjaro) |
| Dosing | Once weekly | Once weekly |
| Maintenance doses in phase 3 | 4, 9, 12 mg | 5, 10, 15 mg |
| Main obesity trial | TRIUMPH-1, 80 weeks | SURMOUNT-1, 72 weeks |
| Weight change, top dose (all randomized) | −25.0% (12 mg) | −20.9% (15 mg) |
| Weight change, placebo | −3.9% | −3.1% |
Sources: TRIUMPH-1[1] and SURMOUNT-1.[3] Both figures in the weight rows use the "all randomized" (treatment-regimen) analysis, the closest like-for-like numbers available.
Weight loss by dose
| Retatrutide (TRIUMPH-1, 80 wk) | Tirzepatide (SURMOUNT-1, 72 wk) | ||
|---|---|---|---|
| 4 mg | −17.6% | 5 mg | −15.0% |
| 9 mg | −23.7% | 10 mg | −19.5% |
| 12 mg | −25.0% | 15 mg | −20.9% |
Side effects and stopping treatment
Both drugs mainly cause stomach side effects. In SURMOUNT-1, 4.3–7.1% of people on tirzepatide stopped because of side effects, against 2.6% on placebo.[3] In TRIUMPH-1 the figures were 4.1–11.3% on retatrutide against 4.9% on placebo.[1] Retatrutide also showed a skin-sensation effect (dysesthesia) in up to 12.5% of people in TRIUMPH-1.[1]
How the doses are reached
Both drugs start low and step up every 4 weeks to limit stomach side effects. Tirzepatide (Zepbound) starts at 2.5 mg and rises in 2.5 mg steps to a maximum of 15 mg.[6] Retatrutide's phase 3 trials started at 2 mg and stepped through 4, 6 and 9 mg to a maximum of 12 mg.[1] The full retatrutide schedule is in the dosage chart.
Mechanism: two receptors or three
Tirzepatide activates GIP and GLP-1 receptors. Retatrutide adds the glucagon receptor. Compared with the body's own hormones, retatrutide is more potent at the GIP receptor and less potent at the GLP-1 and glucagon receptors.[5] Whether the third receptor adds benefit beyond higher weight loss, and at what cost in side effects, is what the head-to-head trial is designed to show. More in what is retatrutide.
Retatrutide vs Zepbound and Mounjaro
Zepbound and Mounjaro are both tirzepatide: Zepbound is the brand for weight management and Mounjaro the brand for type 2 diabetes. So "retatrutide vs Zepbound" and "retatrutide vs Mounjaro" are the same drug comparison as on this page. Zepbound's FDA label gives a starting dose of 2.5 mg and a top dose of 15 mg weekly.[6] Retatrutide has no brand name yet because it is not approved.
Availability and price
Tirzepatide is sold as Zepbound and Mounjaro, with self-pay Zepbound vials from $299 per 4-week supply on LillyDirect. Retatrutide has no price because it is not approved. See retatrutide cost.
Tirzepatide vs retatrutide: the head-to-head trial
TRIUMPH-5 (NCT06662383) is the only trial that compares the two drugs directly. It enrolled about 800 people with obesity and measures weight change at 80 weeks. On November 13, 2026 ClinicalTrials.gov listed it as active, not recruiting, with an estimated primary completion date of November 2026 and no results posted.[4] Until it reports, any claim that one drug "beats" the other rests on separate trials.
| Item | Detail |
|---|---|
| Design | Retatrutide vs tirzepatide, randomized |
| Participants | About 800 adults with obesity |
| Main measurement | Weight change at 80 weeks |
| Status | Active, not recruiting; estimated primary completion November 2026 |
| Results | None posted yet |
Related
- Retatrutide vs semaglutideIncluding the head-to-head result
- All retatrutide resultsEvery trial, both analyses
Frequently asked questions
Is retatrutide better than tirzepatide?
Its trial weight-loss numbers are higher, but no direct comparison has been published. TRIUMPH-5 will answer that question.
What is the difference between retatrutide and tirzepatide?
Tirzepatide activates GIP and GLP-1 receptors. Retatrutide also activates the glucagon receptor. Tirzepatide is approved; retatrutide is not.
When will tirzepatide versus retatrutide results be published?
The head-to-head TRIUMPH-5 trial lists an estimated primary completion date of November 2026. Topline results usually follow completion, but Lilly has not announced a date.[4]
Sources
- Jastreboff AM et al. Retatrutide for obesity (TRIUMPH-1)
- Lilly: retatrutide delivered powerful weight loss in pivotal phase 3 obesity trial (TRIUMPH-1)
- Jastreboff AM et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1)
- Retatrutide studies (NCT04881760, NCT05929066, NCT05931367, NCT06662383, NCT07629401 and others)
- Jastreboff AM et al. Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial
- Zepbound (tirzepatide) prescribing information