Claimed effect · Retatrutide

Does Retatrutide help with body weight?

A
Grade A — established in humans2 phase 3 + 1 phase 2 RCT published; 2 phase 3 topline · effect size: large
Short answerEstablished in humans. 2 phase 3 + 1 phase 2 RCT published; 2 phase 3 topline point the same way: a large effect. TRIUMPH-1, published in the New England Journal of Medicine on 29 September 2026 (2,339 adults with obesity and no diabetes, 80 weeks): −17.6% on 4 mg, −23.7% on 9 mg and −25.0% on 12 mg versus −3.9% on placebo. TRIUMPH-2, published in The Lancet the same day (1,152 adults with obesity and type 2 diabetes, 80 weeks): −11.9%, −16.8% and −18.8% versus −5.1%. Both papers count every participant randomised; the figures first announced by press release, 28.3% and 20.8% on 12 mg, were higher. Phase 2: −24.2% at 48 weeks on 12 mg. Still press releases only: TRIUMPH-4 (−28.7% at 68 weeks vs −2.1% placebo), TRIUMPH-3 (1,949 adults with severe obesity and cardiovascular disease: −22.6% vs −3.2%) and the 104-week TRIUMPH-1 extension in people with a BMI of 35 or more (−30.3%).

What the studies show

TRIUMPH-1, published in the New England Journal of Medicine on 29 September 2026 (2,339 adults with obesity and no diabetes, 80 weeks): −17.6% on 4 mg, −23.7% on 9 mg and −25.0% on 12 mg versus −3.9% on placebo. TRIUMPH-2, published in The Lancet the same day (1,152 adults with obesity and type 2 diabetes, 80 weeks): −11.9%, −16.8% and −18.8% versus −5.1%. Both papers count every participant randomised; the figures first announced by press release, 28.3% and 20.8% on 12 mg, were higher. Phase 2: −24.2% at 48 weeks on 12 mg. Still press releases only: TRIUMPH-4 (−28.7% at 68 weeks vs −2.1% placebo), TRIUMPH-3 (1,949 adults with severe obesity and cardiovascular disease: −22.6% vs −3.2%) and the 104-week TRIUMPH-1 extension in people with a BMI of 35 or more (−30.3%).

“The mean percent change in body weight in the retatrutide groups was -17.6% (4-mg dose), -23.7% (9-mg dose), and -25.0% (12-mg dose) versus -3.9% in the placebo group (differences, -19.8 and -21.0 percentage points, respectively; P<0.001 for both comparisons).”

Verbatim, from the abstractJastreboff AM, et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1). N Engl J Med, 2026 (online 29 Sep)

Several well-run randomised trials in people, pointing the same way. You can plan around this. It still says nothing about whether the effect is worth the side effects for you.

  1. 1
    Jastreboff AM, et al. Retatrutide, a triple hormone receptor agonist, for treatment of obesity (TRIUMPH-1).N Engl J Med, 2026 (online 29 Sep)2,339 randomised, 80 weeks; −25.0% on 12 mg vs −3.9% placebo by intention to treat. Subgroups with knee osteoarthritis (n=574) and obstructive sleep apnoea (n=243). NCT05929066.
  2. 2
    Bellido V, et al. Retatrutide in adults with obesity and type 2 diabetes (TRIUMPH-2): a double-blind, parallel-group, randomised, placebo-controlled, phase 3 trial.Lancet, 2026 (online 29 Sep)1,152 randomised, 92 sites, 80 weeks; −18.8% on 12 mg vs −5.1% placebo (treatment-regimen estimand). NCT05929079.
  3. 3
    Jastreboff AM, et al. Triple-hormone-receptor agonist retatrutide for obesity — a phase 2 trial.N Engl J Med, 2023;389:514–526338 adults; −24.2% at 48 weeks on 12 mg.
  4. 4
  5. 5
    Eli Lilly. Retatrutide TRIUMPH-1 topline results (NCT05929066).Press release, May 20262,339 adults, 80 weeks plus 104-week extension. Detailed data promised for the ADA Scientific Sessions; not peer-reviewed at time of review.
  6. 6
    Eli Lilly. Lilly's triple agonist retatrutide successful in two additional phase 3 obesity trials (TRIUMPH-2, TRIUMPH-3).Press release, 23 Jul 2026TRIUMPH-2: 1,152 adults with obesity and type 2 diabetes, 80 weeks. TRIUMPH-3: 1,949 adults with severe obesity and cardiovascular disease, 80 weeks. Topline; not peer-reviewed. Lilly intends to file with the FDA in Q1 2027.

In context

Retatrutide is an investigational once-weekly peptide that activates three receptors at once: GIP, GLP-1 and glucagon. In TRIUMPH-1, a 2,339-person phase 3 trial published in September 2026, adults with obesity lost 25.0% of body weight at 80 weeks on the top dose against 3.9% on placebo; in adults who also have type 2 diabetes the figure was 18.8% (TRIUMPH-2). A separate published trial cut HbA1c by up to 1.9 percentage points. It is not approved anywhere, and no legitimate supply exists outside clinical trials.

Retatrutide is investigational. Legal status differs by country — see the regulation section or the jurisdiction pages.

Questions

Is Retatrutide proven to help with body weight?
Yes, as far as human trials can show it: 2 phase 3 + 1 phase 2 RCT published; 2 phase 3 topline. LYO grades this outcome A.
What studies are behind the grade?
TRIUMPH-1, published in the New England Journal of Medicine on 29 September 2026 (2,339 adults with obesity and no diabetes, 80 weeks): −17.6% on 4 mg, −23.7% on 9 mg and −25.0% on 12 mg versus −3.9% on placebo. TRIUMPH-2, published in The Lancet the same day (1,152 adults with obesity and type 2 diabetes, 80 weeks): −11.9%, −16.8% and −18.8% versus −5.1%. Both papers count every participant randomised; the figures first announced by press release, 28.3% and 20.8% on 12 mg, were higher. Phase 2: −24.2% at 48 weeks on 12 mg. Still press releases only: TRIUMPH-4 (−28.7% at 68 weeks vs −2.1% placebo), TRIUMPH-3 (1,949 adults with severe obesity and cardiovascular disease: −22.6% vs −3.2%) and the 104-week TRIUMPH-1 extension in people with a BMI of 35 or more (−30.3%).
Is Retatrutide approved for this?
No. Retatrutide is investigational; it is not an approved medicine for any indication in the jurisdictions LYO covers.

Other outcomes for Retatrutide

Written and maintained by LYO Research — how pages are written and checked. Reviewed 7 October 2026. Grades count human evidence only; see how LYO grades. Not medical advice. Correct this page →