The cytochrome p450 system accounts for 70 to 80 percent of the enzymes involved in drug clearance, making it the most important system for drug metabolism. Both THC and CBD are competitive inhibitors of three different enzymes in the cytochrome p450 system, two of which are involved in the metabolism of Xarelto (rivaroxaban). This means that CBD and THC are competing for the same receptors as is Xarelto. So when Xarelto is taken concurrently with CBD and/or THC, Xarelto levels could possibly rise. When Xarelto levels rise excessively, blood clotting may become compromised, leading to signs ranging from frequent bloody noses, all the way on up to a potentially fatal event, such as a hemorrhagic stroke or heart attack.
A case report published in 2009 described a patient who was on coumadin (Warfarin) —the most commonly prescribed blood thinner— therapy for eleven years. He was admitted to the hospital for a severe gastrointestinal bleed when he confessed to consuming much more cannabis than was typical for him; his INR was 10.41 (therapeutic range is usually between 2 and 3); after inpatient treatment, his INR normalized; then, fifteen days after being discharged, he was readmitted with an INR of 11.55; after he quit using cannabis, his INR remained between 1.08 and 4.40 and he suffered no further complications.
Another case report suggested that extremely high doses of CBD can lead to markedly elevated coumadin levels. Enrolled in a clinical trial evaluating CBD as a potential treatment for epilepsy, the test subject was given extremely high doses of CBD. He was first given doses averaging 265mg, which resulted in a slightly elevated coumadin level; at doses averaging 528mg, the coumadin levels were markedly elevated; after reducing the coumadin dose, INR results normalized. Relevantly, very few patients, if any, would ever take as much CBD.
However, as previously mentioned, a highly elevated Xarelto level can lead to serious, even fatal, consequences. And because the effects of cannabis on Xarelto levels have yet to be sufficiently studied, you should discuss the matter with your prescribing physician and monitor your INR results with extra vigilance.
You’re very welcome Colly. CBD and Xarelto would still compete for the same p450 isoenzymes. However, because CBD has low affinity to those isoenzyes, it would take much more than 40mg to affect coagulation. Your anesthesiologist will make sure coagulation isn’t compromised with a blood test prior to surgery. Best of luck!