TRIUMPH-4 Results: Retatrutide Slashes Weight and Relieves Knee Osteoarthritis Pain

Eli Lilly announced topline results from TRIUMPH-4, the first Phase 3 trial to evaluate retatrutide specifically in adults living with both obesity and knee osteoarthritis. The data, released December 11, 2025, marks a major milestone — not just for the drug, but for the millions of patients whose joint pain has been notoriously difficult to treat with pharmacologic weight loss alone. Retatrutide met all primary and key secondary endpoints in the 68-week, randomized, double-blind, placebo-controlled study (NCT05931367). Participants experienced mean weight loss of up to **28.7%** (approximately 71.2 lbs or 32.3 kg) from baseline and reported substantial improvements in knee pain and physical function. ## The data The dual-endpoint design of TRIUMPH-4 set it apart from typical obesity trials. The study measured: - **Weight reduction:** Up to 28.7% mean body weight loss at the highest dose, on par with the results seen in the TRIUMPH-1 obesity trial - **Knee pain (WOMAC Pain subscale):** Clinically meaningful reduction from baseline, sustained over the treatment period - **Physical function (WOMAC Physical Function subscale):** Significant improvement, reflecting real-world mobility benefits - **Safety profile:** Consistent with the GIP/GLP-1/glucagon receptor class; gastrointestinal side effects (nausea, vomiting, diarrhoea) were the most common, with some patients discontinuing due to tolerability, as reported in some analyses of the data The magnitude of pain reduction is particularly noteworthy. Osteoarthritis of the knee is a leading cause of disability worldwide, and weight loss is a first-line recommendation in clinical guidelines — yet most patients struggle to achieve and maintain the 10–15% weight loss typically needed for meaningful symptomatic relief. Retatrutide's ability to deliver bariatric-surgery-level weight loss in a medical context, combined with direct improvements on osteoarthritis-specific endpoints, positions it as a potential dual-indication therapy. ## Why this matters TRIUMPH-4 is the first successful Phase 3 trial of a triple-agonist (GIP/GLP-1/glucagon) in an obesity-related osteoarthritis population. The implications extend beyond simple weight loss: 1. **Mechanism matters:** GIP and glucagon receptor agonism may contribute direct anti-inflammatory or metabolic effects on joint tissues, independent of weight loss. Researchers are investigating whether the triple-agonist mechanism offers benefits that GLP-1 monotherapy cannot. 2. **Broadening the addressable population:** If approved for both obesity and obesity-related knee OA, retatrutide could reach patients who might not otherwise qualify for weight-loss pharmacotherapy alone. 3. **A class effect?** The data raise the question of whether other incretin-based therapies might show similar OA benefits — or whether retatrutide's unique triple-agonist profile is required. ## Canadian context TRIUMPH-4 included **10 Canadian trial sites**, reflecting strong investigator interest from Canadian rheumatology and metabolic disease centres. This is directly relevant to Canadians: osteoarthritis affects approximately **1 in 7 Canadian adults** (about 4.5 million people), and obesity is the single strongest modifiable risk factor for knee OA. For Canadian patients with obesity-related knee OA, the current treatment landscape is limited: - **Weight loss** (lifestyle modification) has poor long-term success rates - **NSAIDs and analgesics** provide symptomatic relief but do not address the underlying drivers of disease - **Joint replacement surgery** is effective but costly to the healthcare system and inaccessible to many - **GLP-1 drugs** (semaglutide, tirzepatide) are not specifically studied for OA endpoints and are not indicated for OA in Canada If retatrutide ultimately receives Health Canada approval for both weight management and obesity-related knee OA, it could fill a substantial therapeutic gap. The Canadian OA population skews older, and many patients have comorbidities — diabetes, cardiovascular disease, hypertension — that overlapping metabolic treatments could simultaneously address. The data will need to be presented at a major medical conference and published in a peer-reviewed journal before any regulatory submission. We will update this page when the full dataset becomes available. ## Sources - [Pharmacy Times — Once-Weekly Retatrutide Reduces Weight and Knee Pain in Patients With Obesity and Osteoarthritis](https://www.pharmacytimes.com/view/once-weekly-retatrutide-reduces-weight-and-knee-pain-in-patients-with-obesity-and-osteoarthritis) - [ClinicalTrials.gov — TRIUMPH-4 (NCT05931367)](https://clinicaltrials.gov/study/NCT05931367) - [HCPLive — TRIUMPH-4: Topline Data Highlights Retatrutide's Significant Weight Loss Effects](https://www.hcplive.com/view/triumph-4-topline-data-highlights-retatrutide-significant-weight-loss-effects) - [Patient Care Online — Retatrutide Achieves Up to 28.7% Weight Loss and Marked Knee Pain Reduction in Phase 3 TRIUMPH-4 Trial](https://www.patientcareonline.com/view/retatrutide-achieves-up-to-28-7-weight-loss-and-marked-knee-pain-reduction-in-phase-3-triumph-4-trial) - [CNBC — Eli Lilly's next-generation obesity drug delivers strong weight loss, reduces knee pain in late-stage trial](https://www.cnbc.com/2025/12/11/eli-lilly-retatrutide-obesity-knee-pain-phase-3.html) - [Fierce Biotech — Lilly's obesity triple threat smashes efficacy expectations in phase 3 but proves intolerable for some](https://www.fiercebiotech.com/biotech/lillys-obesity-triple-threat-smashes-efficacy-expectations-phase-3-proves-intolerable-some) - [BioPharma Dive — Lilly's three-pronged drug puts obesity field 'on notice'](https://www.biopharmadive.com/news/lilly-retatrutide-phase-3-obesity-osteoarthritis/734991/)