Background The stroke severity or functional outcomes could differ because the efficacy of non-vitamin K antagonist oral anticoagulants (NOACs) could be different according to the dose. We investigated whether there was any difference in the stroke outcomes in patients with non-valvular atrial fibrillation (NVAF) by their prior medication status, including standard-dosed versus under-dosed NOACs. Materials and Methods We enrolled 858 patients with acute ischaemic stroke with chronic NVAF admitted at six hospitals in Korea. We categorized their prior medication status as follows: (1) no anti-thrombotics (n = 219), (2) only anti-platelet (n = 347), (3) warfarin with a sub-therapeutic intensity (n = 185), (4) warfarin with a therapeutic intensity (n = 37), (5) under-dosed NOAC (n = 27) and (6) standard-dosed NOAC (n = 43). We compared the initial stroke severity between groups. Results Among the 858 patients, the patients on standard-dosed NOACs had the lowest initial National Institute of Health Stroke Scale (NIHSS) score, followed by those on warfarin with a therapeutic intensity and those on only anti-platelet (p < 0.05). Multivariate analysis demonstrated that the NIHSS score was significantly low in the patients on warfarin with a therapeutic intensity (B, -5.602; 95% confidence interval [CI], -8.636 to -2.568; p < 0.001) or those on standard-dosed NOACs (B, -3.588; 95% CI, -6.405 to -0.771; p = 0.013), while there was no difference in the NIHSS score between the patients not taking any anti-thrombotics and those on warfarin with a sub-therapeutic intensity or under-dosed NOACs. Conclusion Use of warfarin with a therapeutic intensity or standard-dosed NOACs was associated with a relatively mild stroke in the patients with NVAF.
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