Retatrutide knee osteoarthritis trial results (TRIUMPH-4): what the data show
TRIUMPH-4 is the Phase 3 trial that tested Eli Lilly's investigational triple agonist retatrutide in adults with obesity and knee osteoarthritis. It was the first retatrutide Phase 3 trial to report, on 11 December 2025, and it is still the trial people search for when they look up knee osteoarthritis drug results. This page sets out what was measured, what was found, what the numbers do and do not mean, and where regulators stand as of October 2026.
- Design: 445 adults with obesity or overweight and knee osteoarthritis, no diabetes; two retatrutide arms vs placebo; 68 weeks; randomized and double-blind.
- Result: both retatrutide arms met both co-primary goals, body weight and WOMAC knee pain, and all key secondary goals.
- Size of effect: weight change up to −28.7% vs −2.1% on placebo; WOMAC pain change up to −75.8% vs −40.3% (efficacy estimand).
- Caveats: company topline data, not yet a peer-reviewed paper; symptoms measured, not cartilage; more people stopped treatment for side effects on retatrutide.
- Status: retatrutide is not approved anywhere. Lilly plans its US filing in the first quarter of 2027.
How TRIUMPH-4 was designed
The trial is registered on ClinicalTrials.gov as NCT05931367. It enrolled 445 adults who had obesity or overweight plus knee osteoarthritis and did not have diabetes. Participants were randomized in equal groups to one of two retatrutide arms or to placebo, and followed for 68 weeks. Their average weight at the start was 112.7 kg, and 84% had a body mass index of 35 or more.
There were two co-primary endpoints:
- Percent change in body weight from baseline to week 68.
- Change in WOMAC pain, the pain subscale of the Western Ontario and McMaster Universities Osteoarthritis Index, a standard questionnaire in osteoarthritis research. WOMAC physical function was a key secondary endpoint.
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Ad · affiliate links. For laboratory research use only, not for human or veterinary use.The results in numbers
Lilly reported results two ways. The efficacy estimand looks at people who stayed on treatment; the treatment-regimen estimand counts everyone, including those who stopped. Both matter.
| At 68 weeks | Lower retatrutide arm | Higher retatrutide arm | Placebo |
|---|---|---|---|
| Weight change (efficacy) | −26.4% | −28.7% | −2.1% |
| Weight change (treatment-regimen) | −20.0% | −23.7% | −4.6% |
| WOMAC pain change (efficacy) | −75.8% | −74.3% | −40.3% |
| WOMAC pain change (treatment-regimen) | −67.2% | −62.6% | −35.1% |
| WOMAC physical function (efficacy) | −71.8% | −73.7% | −35.6% |
| Completely free of knee pain at week 68 (post hoc) | 14.1% | 12.0% | 4.2% |
| Stopped due to adverse events | 12.2% | 18.2% | 4.0% |
Lilly also reported reductions in non-HDL cholesterol, triglycerides and the inflammation marker hsCRP, and a 14.0 mmHg fall in systolic blood pressure in the higher arm.
How to read these results
- The placebo group improved too. Pain fell by about 40% on placebo, which is common in pain trials. The fair comparison is the gap between retatrutide and placebo, not the raw percentage.
- Pain and function, not joint structure. WOMAC measures symptoms reported by participants. TRIUMPH-4 does not show that retatrutide protects cartilage or slows osteoarthritis.
- Weight and pain are linked. Losing weight reduces load on the knee, so the trial cannot separate a direct effect on the joint from the effect of weight loss.
- Topline, not peer-reviewed. The figures come from Lilly's release and medical news reports of it. Full data were due to be presented at a medical meeting and published later.
- Dose comparisons are not meaningful here. The two arms gave similar pain results; the trial was not designed to pick the best arm for pain.
Side effects reported
As with other incretin-based medicines, the most common adverse events were gastrointestinal. Rates in the two retatrutide arms versus placebo were reported as:
| Adverse event | Lower arm | Higher arm | Placebo |
|---|---|---|---|
| Nausea | 38.1% | 43.2% | 10.7% |
| Diarrhea | 34.7% | 33.1% | 13.4% |
| Constipation | 21.8% | 25.0% | 8.7% |
| Vomiting | 20.4% | 20.9% | 0.0% |
| Dysesthesia (abnormal skin sensation) | 8.8% | 20.9% | 0.7% |
Lilly said discontinuations for adverse events tracked baseline BMI and included some people who stopped because of perceived excessive weight loss. Long-term safety outside trial settings is unknown.
How TRIUMPH-4 fits the wider TRIUMPH program
TRIUMPH-4 was the first of four registrational trials. TRIUMPH-1, the main obesity trial, also contained a knee osteoarthritis sub-study that reported WOMAC pain reductions of up to 73.1% in June 2026. TRIUMPH-2 tested people with type 2 diabetes and TRIUMPH-3 people with cardiovascular disease. Our retatrutide Phase 3 overview covers all four, and our semaglutide vs tirzepatide vs retatrutide comparison explains how the molecules differ.
FDA, EMA and UK status (October 2026)
Retatrutide holds no approval from the FDA, the European Medicines Agency or the UK's MHRA. On its Q2 2026 earnings call, Lilly said it plans to submit a US Biologics License Application in the first quarter of 2027, and that it has data to support submissions for obesity, knee osteoarthritis pain and obstructive sleep apnea. Any site quoting a firm approval date is guessing.
Research-grade retatrutide sold online is not Lilly's trial medicine and is not approved for human use. In the UK the MHRA has raided sites making unlicensed retatrutide pens; see are peptides legal in the UK? For the US picture, see our FDA warning letters tracker and the peptide legal guide.
Frequently asked questions
What were the TRIUMPH-4 results?
In 445 adults with obesity and knee osteoarthritis, both retatrutide arms beat placebo on weight and WOMAC knee pain at 68 weeks: weight change up to −28.7% vs −2.1%, and pain change up to −75.8% vs −40.3% (efficacy estimand).
Does retatrutide treat knee osteoarthritis?
It is not approved for any use. TRIUMPH-4 showed lower pain and better function scores alongside large weight loss, but it measured symptoms, not cartilage, and the results are company topline data.
When will retatrutide be approved?
No approval date exists. Lilly plans to file in the US in the first quarter of 2027, after which FDA review typically takes months.
What side effects were seen in TRIUMPH-4?
Mostly gastrointestinal: nausea, diarrhea, constipation and vomiting. Dysesthesia was reported in up to 20.9% on retatrutide vs 0.7% on placebo, and up to 18.2% stopped for adverse events vs 4.0% on placebo.
Is TRIUMPH-4 published in a journal?
As of October 2026 the results have been released as topline data and reported in medical news; Lilly said full data would be presented at a medical meeting and published later.
Sources
- ClinicalTrials.gov: NCT05931367 (TRIUMPH-4)
- Rheum Live: TRIUMPH-4, retatrutide delivers weight loss and knee osteoarthritis pain relief (11 December 2025)
- HCPLive: TRIUMPH-4 topline data (6 March 2026)
- Eli Lilly Q2 2026 earnings call transcript (filing plans)
- PharmExec: retatrutide TRIUMPH-2 and TRIUMPH-3 results
Research suppliers we have checked
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