Retatrutide cut body weight by a quarter in its big trial, and nearly half on the top dose lost 30%

Evidence check, October 1, 2026

The claim: "Retatrutide, the triple-hormone shot, is the strongest weight-loss drug yet; people lose close to 30% of their body weight."

Our grade: Promising. In large randomized trials, retatrutide caused more weight loss than any approved shot did in its own trials: 25% on average on the top dose, and 30% or more for nearly half of the people who stayed on it. It hasn't been tested head to head against tirzepatide yet, and it isn't approved.

Maya is 38. She has tried every diet her friends swear by, and the weight always comes back. Her doctor brought up Zepbound (tirzepatide) last month. Then, on a morning walk, she heard a podcast about a newer shot that makes people lose close to 30% of their body weight.

So should she start now, or wait for the new one?

Retatrutide matters because weight loss of this size used to take surgery. Two big trials came out on September 29, so we can now check the 30% against the full results.

Where the claim came from

Retatrutide is a weekly shot from Eli Lilly, the maker of Zepbound. Semaglutide (Ozempic, Wegovy) copies one gut hormone, GLP-1. Tirzepatide copies two, GLP-1 and GIP. Retatrutide adds a third, glucagon, which is why it's called the triple-hormone shot [4].

The 30% comes from Lilly's May 21 announcement of its first big trial: people on the top dose lost an average of 28.3%, and 45.3% lost at least 30%, "a level long associated with bariatric surgery" [3]. Headlines and videos ran with it. Peter Attia reviewed the early retatrutide data on his podcast in June [2], and Andrew Huberman discussed it with Dr. Chris Thompson on September 21 [1].

On September 29, the full results came out in the New England Journal of Medicine and The Lancet [5, 6].

What the studies found

The first trial: 24% in 48 weeks

In the 2023 phase 2 trial, 338 adults with obesity were randomly assigned to retatrutide or a placebo (a dummy shot) for 48 weeks [4]. On the top dose, 12 mg, they lost 24.2% of their weight, against 2.1% on placebo. 83% lost at least 15%.

The big trial: 25%, or 28% if you stay on it

TRIUMPH-1 randomized 2,339 adults with obesity but no diabetes to one of three doses or placebo, for 80 weeks, double-blind (neither they nor their doctors knew who got what) [5]. Lilly paid for it, as it did every trial here.

Counting everyone who started, including people who quit the shot, the top dose cut weight by 25.0%, against 3.9% on placebo [5]. Counting only the time people stayed on it, the loss was 28.3% [3]. Both numbers are honest; they answer different questions. The first is what a doctor can expect across all patients; the second is what the drug does when you take it.

Among people who stayed on the top dose, 45.3% lost 30% or more [3]. People with a BMI of 35 or higher who kept going to two years reached 30.3% on average, but that group had already done well and tolerated the drug [3]. The 30% is real, but it is the top end, not the average.

Weight wasn't the only change. Knee pain dropped more than on placebo, and in people with sleep apnea, breathing pauses fell by about 32 an hour against about 10 on placebo [5].

With type 2 diabetes, less

TRIUMPH-2 tested the same doses in 1,152 adults with obesity and type 2 diabetes, also randomized and double-blind for 80 weeks [6]. The top dose cut weight by 18.8%, against 5.1% on placebo. A separate 40-week trial of 537 people with newer diabetes found 15.3% against 2.6% [10]. Still a lot, but not 30%.

How much stronger than Zepbound?

No trial has compared the two drugs directly yet. But tirzepatide's big trial, SURMOUNT-1, was run by the same company and counted weight the same two ways, so the numbers line up fairly well [7].

The gap is about 4 to 6 points. For someone who starts at 248 pounds, the average in TRIUMPH-1, that is about 10 to 14 extra pounds (5 to 6.5 kg). The trials had different people and ran for different lengths of time, so treat it as an estimate.

So back to Maya: most of the benefit is already in a drug she can get today. Waiting would buy a few more points, from a shot that isn't approved yet.

The trade-offs

Side effects were mostly stomach problems and rose with the dose. On 12 mg, 42% had nausea (15% on placebo) and 25% vomited (5%) [3]. One is new: dysesthesia, a tingling, burning or extra-sensitive feeling in the skin, hit 12.5% on 12 mg against 0.9% on placebo. Most cases were mild to moderate and went away during treatment [3]. In the diabetes trial, up to 6% had low blood pressure [6].

11.3% quit the top dose because of side effects, against 4.9% on placebo. On 4 mg, only 4.1% quit, and people still lost 17.6% [3, 5]. Heart rate rose at first in the phase 2 trial, peaked at 24 weeks, then came down [4].

Muscle is the usual worry. In a 189-person body-scan study of people with diabetes, the share of the lost weight that was lean mass (everything that isn't fat or bone) was about the same as with other ways of losing weight [9].

Our grade

The case for the other side: every trial was paid for by Lilly, and the longest ran 80 weeks, plus a two-year extension. Nobody knows yet what years of the drug do, or what happens when people stop. The skin symptom is new for this class. And tirzepatide already gets most people most of the way.

What would change the grade: TRIUMPH-5, the head-to-head trial against tirzepatide [8]; heart outcome results; and data from a few years of use.

What this means for you

• If your doctor offers semaglutide or tirzepatide now, the numbers say there's little to gain by waiting. Tirzepatide cut 21% in its big trial [7].
• Expect about a quarter of your weight on retatrutide's top dose, not 30%. With type 2 diabetes, expect closer to 19% [5, 6].
• Staying on the drug is where the extra comes from. The lower 4 mg dose lost 17.6% with far fewer quitting, so a lower dose you can stay on beats a higher one you can't [3, 5].
• It isn't approved yet. Vials sold online as "research peptides" aren't the tested drug; see our article on peptides.
• Protect your muscle on any of these drugs: about 1.6 g of protein per kg of body weight a day and lifting two or three times a week. See keeping muscle on GLP-1 drugs and our protein target.

What's next

TRIUMPH-5 is testing retatrutide against tirzepatide directly, over 80 weeks; it has stopped enrolling [8]. Other trials are testing it in people with heart and kidney disease. We'll update this article when they report. For more on these drugs, see keeping muscle on GLP-1 drugs, our check of peptides, and how much protein to eat.

Sources

1. Huberman A. Best tools for gut health & weight loss | Dr. Chris Thompson. Huberman Lab, September 21, 2026. https://www.hubermanlab.com/episode/best-tools-for-gut-health-and-weight-loss-chris-thompson
2. Attia P. AMA #86: GLP-1 RAs and muscle loss: new data, better questions, and how to preserve muscle during weight loss. The Peter Attia Drive, June 29, 2026. https://peterattiamd.com/ama86/
3. Eli Lilly. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. Press release, May 21, 2026. TRIUMPH-1 efficacy-estimand results, side effects and 104-week extension. https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-powerful-weight-loss
4. Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-hormone-receptor agonist retatrutide for obesity — a phase 2 trial. N Engl J Med, 2023. 338 adults, randomized, double-blind, placebo-controlled, 48 weeks. Funded by Eli Lilly. https://doi.org/10.1056/NEJMoa2301972
5. Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1). N Engl J Med, 2026. 2,339 adults without diabetes, randomized, double-blind, placebo-controlled, 80 weeks. Funded by Eli Lilly. https://doi.org/10.1056/NEJMoa2604169
6. Bellido V, le Roux CW, Ekinci EI, et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2). Lancet, 2026. 1,152 adults, randomized, double-blind, placebo-controlled, 80 weeks. Funded by Eli Lilly. https://doi.org/10.1016/S0140-6736(26)01861-1
7. Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med, 2022. 2,539 adults, randomized, double-blind, placebo-controlled, 72 weeks. Funded by Eli Lilly. https://doi.org/10.1056/NEJMoa2206038
8. Eli Lilly. A study of retatrutide compared to tirzepatide in adults who have obesity (TRIUMPH-5). ClinicalTrials.gov NCT06662383. Phase 3, randomized, double-blind, 80-week primary end point. https://clinicaltrials.gov/study/NCT06662383
9. Coskun T, Wu Q, Schloot NC, et al. Effects of retatrutide on body composition in people with type 2 diabetes. Lancet Diabetes Endocrinol, 2025. 189 adults, randomized, double-blind, placebo-controlled substudy, 36 weeks. Funded by Eli Lilly. https://doi.org/10.1016/S2213-8587(25)00092-0
10. Bajaj HS, Welch M, Shah P, et al. Efficacy and safety of retatrutide in people with type 2 diabetes and inadequate glycaemic control with diet and exercise (TRANSCEND-T2D-1). Lancet, 2026. 537 adults, randomized, double-blind, placebo-controlled, 40 weeks. Funded by Eli Lilly. https://doi.org/10.1016/S0140-6736(26)00967-0