Aims: To describe inflammatory arthritis (IA) patients initiating biologic diseasemodifying anti-rheumatic drugs (bDMARDs) who use complementary and alternative medicine (CAM), and determine the impact of CAM on predicting modified Health Assessment Questionnaire (mHAQ) at 6 months.Methods: This was a prospective inception cohort study of patients ≥21 years old initiating a bDMARD for IA after July 2016. Data were obtained via questionnaires and abstraction from medical records. Baseline characteristics between ever-CAM and CAM non-users were compared. CAM as a predictor of mHAQ ≥1 at 6 months after bDMARD initiation was analyzed using multivariate logistic regression, adjusting for other baseline characteristics.Results: We recruited 299 patients (36.2% male, mean age 49.0 years). There were 45.8% who had rheumatoid arthritis, 54.2% had a spondyloarthropathy, median disease duration of 1.1 years and median mHAQ of 0.4. Compared to CAM non-users, ever-CAM users had a lower mean body mass index, were less likely to speak English, and more likely to smoke and drink alcohol. There was no association of CAM use with high mHAQ and no interaction with smoking. Smoking (odds ratio [OR] 938.9; 95% CI 3.20-275 884.1), baseline mHAQ (OR 252.2; 95% CI 5.34-11 899.2) and Charlson's Comorbidity Index score ≥4 (OR 237.4;) independently predicted high mHAQ at 6 months.Conclusions: CAM use was not associated with high mHAQ at 6 months. Smoking was an independent predictor of residual functional disability at 6 months, even after adjusting for age, comorbidity and baseline mHAQ. Greater emphasis on smoking cessation may improve long-term functional outcomes in IA patients on bDMARDs.