Are there interactions between blood thinners and marijuana?

That is an excellent question. There have been a few studies that seem to indicate that high doses of CBD can inactivate some enzymes in the liver that metabolize some blood thinners such as warfarin. These enzymes are the cytochrome P450 enzymes (CYP) and have a role in many metabolic pathways.There is no clearly established cut-off dose, below which CBD does not interact with other drugs. A 2013 report on a clinical trial using GW Pharmaceutical’s Sativex, a whole plant CBD-rich sublingual spray, found no interactions with CYP enzymes when approximately 40mg of CBD were administered. Whether or not any amount of CBD makes bleeding times longer is still a question that has not been satisfactorily answered. If you are taking blood thinners it would be wise to inform your physician to that fact so that they can monitor your bleeding times appropriately.

Perry Solomon, MD