Thanks to hemostasis expert and colleague Dave McGlasson for a recent phone discussion on the effects of marijuana on warfarin therapy [disclaimer: no personal experience]. A literature search turned up several studies and meta-analyses associating THC with markedly raised INR, implying an effect on the cytochrome oxidase pathway. Click review article Damkier P, Lawwen D, Christensen MMH, et al. Interaction between warfarin and cannabis. BCPT 2019;124:28–31 doi: 10.1111/bcpt.13152 for a complete discussion. We found no article implicating CBD preperations affecting the INR.
See Dave McGlasson’s comment below. To access the Dave references, article, click Grayson L, Vines B, Nichol K, et al. An interaction between warfarin and cannabidiol, a case report. Epilepsy & Behavior Case Reports 2018;9: 10–11.
I just discovered an article
Dave found Grayson L, Vines B, Nichol K, et al. An interaction between warfarin and cannabidiol, a case report. Epilepsy & Behavior Case Reports 2018;9: 10–11 [attached to original post above].
Abstract: An interaction between warfarin and cannabidiol is described. The mechanisms of cannabidiol and warfarin metabolism are reviewed. Mechanism of the interaction is proposed: INR should be monitored in patients when cannabinoids are introduced.