Tirzepatide vs retatrutide: what the trials show so far

No published trial has compared tirzepatide and retatrutide directly. Eli Lilly is running one, registered as NCT06662383: a randomized, double-blind phase 3 study in adults with obesity, with an estimated enrollment of 800 and a primary endpoint of percent change in body weight at week 80. ClinicalTrials.gov lists it as active and no longer recruiting, with primary completion estimated for November 2026 (record updated July 20, 2026). Until it reports, the only comparison available is between separate trials, and those cannot be ranked.

What does each drug target?

Tirzepatide activates two receptors, GIP and GLP-1. It is sold as Zepbound for chronic weight management and as Mounjaro. Retatrutide activates those two and the glucagon receptor as well. Whether the glucagon addition explains any of retatrutide's larger numbers is unresolved, as our incretin receptor article lays out: none of the papers we opened isolates what each receptor contributes.

What did the separate trials report?

Read quickly, the table suggests retatrutide wins. The trials do not support that reading. Weight keeps falling for longer in an 80-week trial than in a 48-week one, populations and analysis methods differ, and the TRIUMPH-1 numbers come from a sponsor announcement relayed by trade press rather than from a peer-reviewed paper. The same sponsor, Lilly, makes both drugs.

How do the side-effect signals compare?

In SURMOUNT-1, adverse events led to discontinuation in 4.3%, 7.1% and 6.2% of the three tirzepatide groups versus 2.6% on placebo, and gastrointestinal events were the most common. In TRIUMPH-1, adverse-event discontinuation was 4.1%, 6.9% and 11.3% across the three retatrutide arms versus 4.9% on placebo. Dysesthesia, an abnormal skin sensation, occurred in 5.1%, 12.3% and 12.5% of the retatrutide arms versus 0.9% on placebo. We found no matching figure in the SURMOUNT-1 abstract, so a clean comparison of that signal is not possible from published data.

What will the head-to-head trial add?

It will put both drugs in one randomized population with one analysis plan, which is the design that removes the cross-trial problem. Our semaglutide versus tirzepatide article shows how much a direct comparison can change the reading: SURMOUNT-5 found -20.2% against -13.7% at 72 weeks in 751 adults. When the retatrutide result appears, the useful questions will be the size of the gap, how many people stopped treatment, and whether the side-effect signals hold up in a trial that includes tirzepatide. We will update this page when it reports. The registry entry says participants must have obesity and at least one self-reported unsuccessful dietary attempt. It excludes people whose weight changed by more than 5 kg in the 90 days before screening, who have had or plan surgical, endoscopic or device-based obesity treatment, or who took weight-loss drugs in the prior 90 days. In the tirzepatide and semaglutide case, the separate trials (STEP 1 and SURMOUNT-1) and the later direct trial pointed the same way. That does not guarantee the same for retatrutide, where the trial lengths differ more.

Which of the two is approved?

Tirzepatide is. Its pivotal SURMOUNT-1 trial randomized 2,539 adults with obesity, or overweight plus a weight-related complication, to three tirzepatide groups or placebo for 72 weeks. The FDA approved Zepbound for chronic weight management on November 8, 2023. None of the sources we opened, checked on October 8, 2026, report a retatrutide approval in any country. Lilly's second-quarter 2026 earnings release, dated August 5, 2026, says the company plans to submit a Biologics License Application to the FDA in the first quarter of 2027. Our retatrutide results article covers the trials in more detail, and the retatrutide pricing article explains why no official price exists yet.

Research-grade tirzepatide or retatrutide is not the approved product and is not the drug used in any of these trials. Anyone seeking weight management should talk to a physician about approved options.

Quick answers

• Is retatrutide better than tirzepatide? Unknown. No head-to-head result is published, and Lilly's NCT06662383 trial is the one to watch.
• Is retatrutide the same as Zepbound or Mounjaro? No. Those are brand names of tirzepatide, which targets two receptors. Retatrutide targets three.
• Which has more weight loss in trials? Retatrutide's separate trials reported larger numbers (-24.2% to -28.3%) than tirzepatide's SURMOUNT-1 (-20.9%), but the trials differ in length, population and reporting source.
• When will the comparison trial report? ClinicalTrials.gov estimates primary completion in November 2026. The date can change.
• Is retatrutide available to prescribe? No approval was found in the sources we opened, and the FDA says retatrutide cannot be used in compounding.

Bottom line

Tirzepatide has the stronger, approved, peer-reviewed record. Retatrutide has larger reported numbers from shorter or sponsor-reported trials and a head-to-head result still to come. Read the tirzepatide and retatrutide profiles for status, and use the price comparison table for research-material pricing at two suppliers.