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Objective: Previous observational studies have yielded conflicting results on whether medication adherence differs between patients receiving warfarin and direct oral anticoagulants (DOACs). Importantly, no study has adequately accounted for warfarin dosing being continuously modified based on INR values while dosing of DOACs is fixed. We aimed to compare non-adherence between new users of apixaban, dabigatran, rivaroxaban and warfarin in a population-based cohort., Methods: New users of apixaban, dabigatran, rivaroxaban and warfarin from 2014 to 2019 living in the Icelandic capital area were included. Non-adherence was defined as proportion of days covered below 80%. Inverse probability weighting was used to yield balanced study groups and non-adherence was compared using logistic regression. Factors associated with non-adherence were estimated using multivariable logistic regression., Results: Overall, 1266 patients received apixaban, 247 dabigatran, 1566 rivaroxaban and 768 warfarin. The proportion of patients with non-adherence ranged from 10.5% to 16.7%. Dabigatran was associated with significantly higher odds of non-adherence compared with apixaban (OR 1.57, 95% CI 1.21 to 2.04, p<0.001), rivaroxaban (OR 1.45, 95% CI 1.12 to 1.89, p=0.005) and warfarin (OR 1.63, 95% CI 1.23 to 2.15, p<0.001). The odds of non-adherence were similar for apixaban, rivaroxaban and warfarin. Apart from the type of oral anticoagulants (OACs) used, female sex, hypertension, history of cerebrovascular accident and concomitant statin use were all independently associated with lower odds of non-adherence., Conclusion: Dabigatran was associated with higher odds of non-adherence compared with other OACs. Non-adherence was similar between apixaban, rivaroxaban and warfarin users. Female sex and higher comorbidity were associated with better medication adherence., Competing Interests: Competing interests: PTO and BRG together with the Landspitali University Hospital and the University of Iceland hold a patent for the Fiix-prothrombin measurement. All other authors declare no competing interests., (© Author(s) (or their employer(s)) 2023. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)