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Status: retatrutide is not approved for sale or use anywhere in the world, including the UK. Anything sold as retatrutide is unlicensed and illegal to supply.

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The evidence, in numbers

Retatrutide trial results: what the data actually says

The weight-loss figures behind the headlines are real and peer-reviewed or company-reported. Here is every major result, with the numbers, the populations, and the caveats that usually get left out.

Independently written · Last reviewed: · editorial policy

Key facts in 30 seconds

  • TRIUMPH-1 (pivotal): −28.3% average body weight at 80 weeks on 12 mg; 45.3% lost ≥30%; the 104-week extension reached −30.3% in participants with BMI ≥35.
  • TRIUMPH-2 (with type 2 diabetes): −20.8% at 80 weeks, HbA1c down ~1.6%. TRIUMPH-3 (severe obesity with cardiovascular disease): −22.6%.
  • TRIUMPH-4 (knee osteoarthritis): −28.7% at 68 weeks. TRANSCEND-T2D-1: HbA1c −2.0%, weight −16.8% at 40 weeks.
  • TRIUMPH-5 — the head-to-head against tirzepatide (Mounjaro) — reports late 2026/2027; until then cross-trial comparisons are extrapolations, not findings.
  • All figures are trial averages with intensive clinical support — not promises of individual results.

The headline numbers

StudyPopulationResult at top doseReported
Phase 2 (Jastreboff, NEJM)Adults with obesity, without diabetes−24.2% body weight at 48 weeks (12 mg)June 2023
TRIUMPH-1 (pivotal)2,339 adults with obesity or overweight plus a weight-related condition, without diabetes−28.3% at 80 weeks (12 mg); 45.3% of participants lost ≥30%. Extension to 104 weeks reached −30.3% in participants with BMI ≥3521 May 2026
TRIUMPH-2Obesity or overweight with type 2 diabetes−20.8% at 80 weeks (12 mg); HbA1c down up to ~1.6%23 July 2026
TRIUMPH-3Severe obesity with established cardiovascular disease−22.6% at 80 weeks (12 mg), with improvements in triglycerides, blood pressure and other risk markers23 July 2026
TRIUMPH-4Obesity with knee osteoarthritis−28.7% at 68 weeksDecember 2025
TRANSCEND-T2D-1Type 2 diabetesHbA1c −2.0%; weight −16.8% at 40 weeksMarch 2026
TRIUMPH-5 (head-to-head vs tirzepatide)ObesityNot yet reported; study completion expected around December 2026Expected late 2026 / 2027

How to read these numbers honestly

  • These are averages in trials, not promises. TRIUMPH-1's 28.3% is a group average at the highest dose over 80 weeks, in participants who had regular clinical contact, structured lifestyle support and high adherence. Individual results will spread widely around that average.
  • Placebo-adjusted thinking matters. Lifestyle support alone produced meaningful weight loss in these trials' placebo arms. The medicine's added effect is what regulators will judge, and it is large — but the headline total overstates what the molecule alone does.
  • Cross-trial comparison is slippery. Tirzepatide's SURMOUNT-1 (−20.9% at 72 weeks) and semaglutide's STEP 1 (−14.9% at 68 weeks) had different lengths, populations and designs. The clean comparison everyone wants — retatrutide versus tirzepatide directly — is TRIUMPH-5, and it has not reported yet. Until it does, “roughly a third more effective than Mounjaro” style claims are extrapolations, not findings.
  • Topline ≠ full paper. The July 2026 TRIUMPH-2 and TRIUMPH-3 figures are company announcements. Full methodological detail arrives with peer-reviewed publication; numbers can shift slightly.
  • Diabetes populations lose less weight. TRIUMPH-2's 20.8% is not a disappointment; it matches the pattern seen across the whole medicine class, where type 2 diabetes blunts weight loss.

What the trials also measured

Beyond the scale, the programme reported improvements in waist circumference, blood pressure, triglycerides, HbA1c and inflammatory markers — and earlier-phase imaging substudies showed large reductions in liver fat, which is why retatrutide is also being studied in MASLD (fatty liver disease). The cardiovascular outcomes trial that regulators and NICE will eventually care about most, TRIUMPH-Outcomes, runs until around 2029.

Why this matters for UK patients

NICE appraisals weight long-term outcomes heavily. The pattern from tirzepatide — rapid private availability after MHRA authorisation, but a phased NHS rollout taking years — is the realistic template for retatrutide too. Our UK timeline page maps what happens, in what order, and roughly when.

Cite this page

Johnson N. Yezz — independent UK retatrutide information. Medstack Ltd, 10 September 2026. https://yezz.co.uk/trial-results

Sources

Every factual claim on this page traces to one of these primary sources. We link out so you can check the original.

  1. 1.Eli Lilly TRIUMPH-1 topline announcement (21 May 2026) and trial history — includes TRIUMPH-2 and TRIUMPH-3 toplines of 23 July 2026
  2. 2.Retatrutide FDA approval timeline and trial tracker — TRIUMPH-5 registry dates and remaining programme
  3. 3.Jastreboff et al., New England Journal of Medicine (2023) — Phase 2 results
  4. 4.Retatrutide Phase 3 status summary — independent status review, August 2026