Retatrutide knee osteoarthritis pain falls in two Phase 3 trials shown at ACR

Eli Lilly will put retatrutide knee osteoarthritis data in front of rheumatologists this week, with a plenary talk at ACR Convergence 2026 in Orlando. The retatrutide knee osteoarthritis results come from two Phase 3 trials, TRIUMPH-4 and TRIUMPH-1, in which the company says knee pain scores fell by close to three quarters from baseline at best. The weekly triple agonist stays in Phase 3 on our board. The release adds detail, but it leaves out the placebo results, trial sizes and safety numbers that decide how much the pain gains really mean.

Two Phase 3 trials reach the ACR plenary stage

Lilly announced on 5 November that it will present new clinical and real world research at the American College of Rheumatology meeting, which runs from 6 to 11 November in Orlando. The lead item is a plenary slot on Sunday 8 November for TRIUMPH-4, a 68 week randomized Phase 3 trial of once weekly retatrutide in adults with knee osteoarthritis pain and obesity or overweight. A second retatrutide abstract, from the 80 week TRIUMPH-1 trial, which tested three dose levels in adults with knee osteoarthritis and obesity, follows as a poster on Tuesday 10 November. According to the company, the plenary covers knee pain, physical function and weight loss together, which is the mix rheumatologists will weigh.

Lilly frames the work around what it calls immunometabolic health. The company cites estimates that about 80% of people with knee osteoarthritis have obesity or overweight, and it notes that treatment guidelines already advise weight loss. "For many people living with knee osteoarthritis pain or psoriatic arthritis, obesity can compound the challenges of managing their condition, affecting how they feel and function every day," said Adrienne Brown, president of Lilly Immunology. For the pipeline, the point is simpler. The retatrutide knee osteoarthritis program is one of several Phase 3 efforts Lilly lists for the molecule, alongside obesity, type 2 diabetes, sleep apnea, chronic low back pain, cardiovascular and renal outcomes, and fatty liver disease.

What the WOMAC pain score numbers show and leave out

In TRIUMPH-4, the company says retatrutide lowered knee pain by up to an average of 4.5 points on the WOMAC pain subscale, from an average starting score of 6.0. Lilly expresses that change as a 75.8% drop from where patients began. In TRIUMPH-1 the best figure was 4.3 points, or 73.1%, from the same baseline. More than one in eight treated patients in TRIUMPH-4, and more than one in six in TRIUMPH-1, reported no knee pain at all when the trials ended. The phrase "up to" matters here. It suggests these figures describe the strongest dose groups rather than every patient on the drug, and the release does not say how the lower doses performed.

More than one in eight treated patients in TRIUMPH-4, and more than one in six in TRIUMPH-1, reported no knee pain at all when the trials ended.

Two caveats sit in the footnotes. Lilly states that the percent change in the WOMAC pain score was not a pre-specified measure and was estimated in a post hoc analysis, so the 75.8% and 73.1% figures are a later way of reading the data, not the tested endpoint. The release also gives no placebo arm results, no patient numbers, no weight loss figures and no rates of side effects or dropouts. Without the placebo change, readers cannot tell how much of the relief belongs to the drug, since pain is a self reported outcome that can also improve in control groups. Those answers should come with the plenary slides and, later, a journal paper.

Tirzepatide psoriatic arthritis data run alongside

The same release covers tirzepatide, Lilly's approved GIP and GLP-1 peptide sold as Zepbound for obesity. In the Phase 3b TOGETHER-PsA trial, adults with psoriatic arthritis and obesity or overweight received the IL-17A antibody Taltz with or without tirzepatide. At week 52, 43.7% of patients on the combination reached ACR50, a common arthritis response yardstick, against 15.7% on Taltz alone, the company said. Lilly adds that the combination group kept improving after week 36 and that disease activity, metabolic and patient reported outcomes also favoured it. The full results go to an oral session on Wednesday 11 November, with posters on early disease control, cardiovascular risk factors and economic modelling.

Here too the fine print counts. Lilly notes that the week 52 analyses were pre-specified but exploratory, with no control for multiplicity, and that comparisons between time points are descriptive. That makes the 43.7% figure supportive rather than confirmatory. Any tirzepatide psoriatic arthritis claim would be a label question, not a stage move, because the drug is already approved on our board. The trial asks whether adding it to an existing biologic helps joints as well as weight. Taltz itself is an antibody rather than a peptide, so it sits outside our tracker. The combination data matter mainly because they carry Lilly's incretins into rheumatology clinics, the same doors retatrutide hopes to open.

What this changes for the triple agonist

For retatrutide, the ACR data change the case more than the stage. The triple agonist, a single peptide that acts on GIP, GLP-1 and glucagon receptors, was already in late development across obesity and diabetes, and our report on its sleep apnea results pointed to a first US filing in early 2027. A retatrutide knee osteoarthritis claim would add a second kind of benefit beyond weight: a symptom that patients feel and that rheumatologists treat. If the full data hold up, Lilly could argue that the drug eases a painful joint disease, not only a number on the scale. The release reports no head to head knee trial against another incretin, so any ranking would be guesswork.

The open questions are about the price of that benefit. In the Ozempic head to head trial, more people stopped the higher retatrutide dose for adverse events than stopped the comparator. The knee pain readouts give no tolerability data yet, so that trade off is still unmeasured in people whose main complaint is a painful joint rather than weight alone. Retatrutide also remains unapproved. Lilly states that it cannot be legally sold or marketed for human use, and Malaysia's health ministry has reported seizing unregistered retatrutide in a series of raids. Product sold outside a trial carries unknown contents, possible counterfeits and no medical oversight. Legitimate access today runs only through registered clinical studies.

Conclusion

The retatrutide knee osteoarthritis readouts strengthen the drug's case without moving it on the board. Two Phase 3 trials show large drops in knee pain scores, but the headline percentages come from a post hoc analysis, and the release withholds placebo, weight and safety figures. The 8 November plenary is where those gaps should start to close. Until a regulator reviews the full package, retatrutide remains an investigational Phase 3 medicine, and these results describe research findings rather than treatment advice.