AbstractObjectiveTo examine the effects of filgotinib, an oral, selective Janus kinase 1 inhibitor, on health-related quality of life (HRQoL) using the Psoriatic Arthritis Impact of Disease (PsAID)9 questionnaire in active PsA.MethodsPatients were randomized 1 : 1 to filgotinib 200 mg or placebo once daily for 16 weeks in EQUATOR, a multicentre, double-blind, phase 2 randomized controlled trial. HRQoL was assessed with PsAID9 at Weeks 4 and 16. Change from baseline in total and individual domain scores, plus the proportions of patients achieving minimal clinically important improvement (MCII; ⩾3 points) and patient-accepted symptom status (PASS; score <4), were evaluated. Correlation with the 36-item short-form health survey (SF-36) was investigated.ResultsOne hundred and thirty-one patients were randomized to filgotinib or placebo. Filgotinib effects on PsAID9 were observed from Week 4. At Week 16, mean (s.d.) change from baseline in PsAID9 was –2.3 (1.8) and –0.8 (2.2) for filgotinib and placebo, respectively (least-squares mean of group difference –1.48 [95% CI –2.12, –0.84], P < 0.0001), with significant improvements in all domains vs placebo. Significantly more patients on filgotinib achieved MCII (group difference 25.4% [95% CI 8.92, 39.99], P = 0.0022) and PASS (group difference 29.6% [95% CI 10.65, 45.60], P = 0.0018) at Week 16 vs placebo. Similar improvements in SF-36 were observed, with moderate to strong negative correlation between PsAID9 and SF-36.ConclusionFilgotinib significantly improved HRQoL vs placebo in patients with active PsA, as measured by PsAID9. To our knowledge, EQUATOR is the first randomized controlled trial to evaluate PsAID9.Trial registrationClinicalTrials.gov, https://clinicaltrials.gov/ct2/show, NCT03101670.