CBD and Warfarin

CBD (cannabidiol) is taken by many to help relieve the debilitating effect of osteoarthritis in both humans and pets (https://curtisswift.com/cbd-for-pets/).  Care needs to be taken, however, when you and I take CBD along with Warfarin prescribed as a blood thinner.  Or, when your veterinarian prescribes it for your pet. In dogs, it is used primarily for long-term thromboprophylaxis (when a blood clot forms in a deep vein).

Past research has indicated an interaction between warfarin and marijuana smoking, resulting in increased international normalized ratio (INR) values and bleeding complications by inhibiting the breakdown of  Warfarin (https://pubmed.ncbi.nlm.nih.gov/19531696/). The cannabinoids, THC, the psychoactive component of Cannabis,  CBD (cannabidiol), and CBN (cannabinol) have all been shown to cause this problem (https://pubmed.ncbi.nlm.nih.gov/16644197/). The extent of the problem and how to adjust your medication is determined by a test to evaluate blood clotting, in other words to determine the blood thinning effect when Warfarin and a cannabinoid are taken orally.

This time test is expressed as an international normalized ratio (INR). “When the INR is higher than the recommended range, it means that your blood clots more slowly than desired, and a lower INR means your blood clots more quickly than desired.” For more info on this testing procedure and what the numbers mean, check out the Mayo Clinic post.

Test to determine how CBD and Warfarin interact

To ensure there are no complications when taking CBD and Warfarin orally, your physician can monitor your International Normalized Ratio (INR). In a 2018 study, a patient’s warfarin dose needed to be reduced by approximately 30% due to the enhancing effect of CBD to prevent excessive bleeding. Check out the report at https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5789126/. The authors of this study recommend your INR be monitored whenever you are taking CBD with Warfarin.

In a 2020 research report, the researchers reported a patient required a nearly 20% warfarin dose reduction to maintain an INR within the safe goal range after starting therapy with cannabidiol. (https://pubmed.ncbi.nlm.nih.gov/33016308/)