- Design
- Phase 3b randomised trial, 52 weeks
- Population
- 271 adults with active psoriatic arthritis and overweight with comorbidity or obesity
- Primary outcome
- ACR50 plus ≥10% weight loss at 36 weeks
- Effect
- 31.7% vs 0.8%; ACR50 33.5% vs 20.4% (P = 0.02)
TOGETHER-PsA was a phase 3b randomised trial (Arthritis & Rheumatology, March 2026) in 271 adults with active psoriatic arthritis and obesity, or overweight with at least one weight-related comorbidity. All received ixekizumab; half also received tirzepatide, both at US-approved doses.
The primary endpoint, ACR50 plus at least 10% weight loss at 36 weeks, was met by 31.7% with combination therapy and 0.8% with ixekizumab alone. More informative is the key secondary endpoint: ACR50 alone was 33.5% vs 20.4% (P = 0.02), with separation from week 4. Minimal disease activity, skin scores, physical function and fatigue also favoured the combination, and safety was consistent with each drug alone.
Most people with psoriatic arthritis carry excess weight, which is linked to poorer response to biologics. This trial suggests treating obesity is part of treating the arthritis. Access and cost will limit this approach in many settings, but the principle applies to any effective weight intervention.
- Measure weight and BMI at every psoriatic arthritis review.
- Consider adding a weight-loss intervention, including a GLP-1-based drug where appropriate, for patients with obesity and active disease.
- Discuss weight as part of the arthritis treatment plan, not a separate issue.
- Expect early joint benefit; the combination separated from monotherapy by week 4.
- Check contraception and pregnancy plans before starting tirzepatide.
Why it matters
It reframes obesity in psoriatic arthritis from a comorbidity to a treatment target that changes joint outcomes.
Don't overread it
The primary endpoint included weight loss, so it was bound to favour the combination; the ACR50 difference is the clinically relevant result.
The statistics, in plain English
ACR50 means at least 50% improvement in joint counts and other measures. A rise from 20.4% to 33.5% means about one extra responder for every eight patients treated with the combination.
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