BACKGROUND: Preclinical studies have shown that baclofen may reduce the risk of osteoarthritis through its anti-inflammatory effect. OBJECTIVE: We aimed to clarify this association by comparing the risks of osteoarthritis and joint replacement surgery in patients receiving baclofen and tizanidine. METHODS: This retrospective cohort study was conducted on the global TriNetX platform (October 31, 2024). New users of baclofen and tizanidine aged ≥40 years were included in the baclofen and tizanidine group, respectively. The propensity score matching method was used. The primary outcomes were osteoarthritis and joint replacement surgery. The secondary outcomes included all-cause mortality, a composite outcome of osteoarthritis and all-cause mortality, and a composite outcome of joint replacement surgery and all-cause mortality. Cause specific hazard ratios (HRs) with 95% confidence intervals (CIs) of the outcomes were calculated with Cox regression using the TriNetX platform. RESULTS: Two well-balanced groups containing 68,210 patients each were generated by propensity score matching (age: 57.8 years
female: 55.6% in both groups). Baclofen users had a significantly lower risk of developing osteoarthritis than tizanidine users (HR: 0.965, 95% CI: 0.941 to 0.989). A similar relationship was observed for joint replacement surgery (HR: 0.847, 95% CI: 0.750 to 0.956). However, the composite outcome of osteoarthritis or death had a HR of 1.129 (95% CI: 1.109 to 1.150), and the HR of joint replacement surgery or death was 1.509 (95% CI: 1.463 to 1.556). The HR of death was 1.577 (95% CI: 1.527 to 1.629), suggesting a higher risk of mortality in the baclofen group. CONCLUSION: The surviving baclofen users had a lower risk of osteoarthritis and joint replacement surgery compared to surviving tizanidine users. However, baclofen users exhibited a higher risk of mortality than tizanidine users. Future studies are necessary to clarify the impact of baclofen on osteoarthritis and joint replacement surgery while accounting for mortality.