Retatrutide vs Tirzepatide: How "Reta" Compares With Zepbound and Mounjaro

Tirzepatide is a dual agonist and retatrutide is a triple agonist. Tirzepatide activates the GIP and GLP-1 receptors.4 Retatrutide activates the GIP, GLP-1 and glucagon receptors.3 Both are weekly injections made by Eli Lilly.1,4

In TRIUMPH-1, adults with obesity on retatrutide 12 mg lost an average of 28.3% of body weight at 80 weeks, against 2.2% on placebo.1 On 4 mg and 9 mg, average losses were 19.0% and 25.9%.1 In a subgroup followed to 104 weeks, the 12 mg group averaged 30.3%.1

In SURMOUNT-1, the trial behind Zepbound, adults with obesity on tirzepatide 15 mg lost an average of 20.9% at 72 weeks, against 3.1% on placebo.4 On 5 mg and 10 mg, losses were 15.0% and 19.5%.4

These numbers come from different trials with different lengths and analysis methods, so they cannot be compared precisely. The Zepbound figures count everyone randomized; Lilly's retatrutide figures are topline results from press releases, not yet an FDA label.1,4 A direct comparison is underway: TRIUMPH-5 randomizes about 800 adults with obesity to retatrutide or tirzepatide for 80 weeks, with primary completion estimated for November 2026.10

In TRIUMPH-2, adults with type 2 diabetes and obesity or overweight lost an average of 12.7%, 19.1% and 20.8% on retatrutide 4 mg, 9 mg and 12 mg at 80 weeks, against 4.0% on placebo.2 In TRIUMPH-3, adults with severe obesity and cardiovascular disease lost 21.6% and 22.6% on 9 mg and 12 mg.2 Tirzepatide for type 2 diabetes is sold as Mounjaro, which is approved to improve blood sugar and reduce cardiovascular risk in adults with type 2 diabetes.5 Our Mounjaro vs Zepbound comparison explains how the two tirzepatide brands differ.

Yes, in part. Retatrutide activates the GLP-1 receptor, but it also activates the GIP and glucagon receptors, which is why it is called a triple agonist.3 "Reta" is shorthand for retatrutide. Some people call it "GLP-3," but no hormone by that name exists.

Retatrutide mimics three gut and pancreatic hormones at once. Like tirzepatide, it activates GLP-1 and GIP receptors, which reduce appetite and slow stomach emptying.3,4 The added glucagon-receptor activity is the part tirzepatide lacks.3 The phase 2 trial also found dose-dependent increases in heart rate that peaked at 24 weeks and then declined.3

Weight loss with retatrutide starts within the first months and keeps building for more than a year. In the phase 2 trial, the 12 mg group had lost an average of 17.5% of body weight at 24 weeks and 24.2% at 48 weeks.3 In TRIUMPH-1, the top dose reached 28.3% at 80 weeks and 30.3% at 104 weeks in the extension group.1 For comparison, see how long Zepbound takes to work.

Both drugs mainly cause stomach side effects. In TRIUMPH-1, nausea occurred in 28.6% to 42.4% of people on retatrutide, diarrhea in 25.2% to 34.1% and vomiting in 10.6% to 25.3%, depending on dose.1 Dysesthesia, an abnormal skin sensation, occurred in 5.1% to 12.5%.1 Side effects led 4.1% to 11.3% to stop treatment.1

On the Zepbound label, nausea affected 25% to 29% of people across doses, diarrhea 19% to 23% and vomiting 8% to 13%, against 8%, 8% and 2% on placebo.4 The figures come from different trials, so treat the comparison as rough. For tirzepatide in detail, see Zepbound side effects.

Retatrutide and Ozempic are different drugs for different uses. Ozempic is semaglutide, a GLP-1-only agonist approved for type 2 diabetes, not weight loss.7 The weight-loss version of semaglutide is Wegovy, whose 2.4 mg injection produced an average loss of 14.9% at 68 weeks.6 Retatrutide's top dose produced 28.3% at 80 weeks in TRIUMPH-1, in a separate trial.1 To compare the approved options, see Wegovy vs Zepbound.

Zepbound and Mounjaro both contain tirzepatide, so the comparison above applies to both.4,5 The practical difference is that Zepbound and Mounjaro can be prescribed and filled today, and retatrutide cannot. Zepbound costs from $299 a month at Lilly's self-pay prices.11 Current prices are on the Zepbound cost page and our cheapest Zepbound ranking.

No. As of October 2026, retatrutide is investigational and not approved anywhere in the world.9 After TRIUMPH-2 and TRIUMPH-3, Lilly said it plans to submit retatrutide to the FDA in the first quarter of 2027.2 Until that submission is filed and reviewed, retatrutide cannot be prescribed outside clinical trials.

Retatrutide sold online is not a legal medicine. The FDA says retatrutide cannot be used in compounding under federal law and has not been found safe and effective for any condition.8 The FDA has warned companies selling retatrutide labeled "for research purposes" or "not for human consumption," and says these products are of unknown quality and may be harmful.8 It has also warned telehealth companies for marketing retatrutide to consumers.8 In August 2026, Lilly said it had found more than 14,000 unlawful online listings and filed six lawsuits against US sellers.9

Is retatrutide stronger than tirzepatide? In separate trials it produced more weight loss: 28.3% at 80 weeks on 12 mg, against 20.9% at 72 weeks on tirzepatide 15 mg.1,4 TRIUMPH-5 is testing them head to head.10

Is retatrutide safe? It has not completed FDA review. Trials reported mostly stomach side effects, plus dysesthesia and heart-rate increases.1,3

When will retatrutide be available? Not before an FDA decision on a submission Lilly plans for the first quarter of 2027.2

Can I switch from tirzepatide to retatrutide? Not legally outside a clinical trial, because retatrutide is not approved or compoundable.8

Is tirzepatide available in pill form? No. Tirzepatide is only an injection.4 See GLP-1 pills vs injections.

Retatrutide is not an option yet. To start an approved tirzepatide today, compare programs in our brand-name GLP-1 ranking or read how to get Zepbound.

This article is for information only and is not medical advice. Retatrutide is an investigational drug that is not approved for any use. Tirzepatide is a prescription drug with real risks and side effects. Talk to a licensed clinician before starting, stopping or changing any treatment.