Cannabis - Warfarin Interaction

Interaction Details

Warfarin is classified as belonging to the following category: Cytochrome P450 2C9 (Cyp2C9) Substrates

Theoretically, cannabis might increase the levels and adverse effects of CYP2C9 substrates.
In vitro research shows that the cannabis constituents delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabinol moderately inhibit the CYP2C9-mediated 7-hydroxylation of S-warfarin in a concentration-dependent manner.

Interaction Rating

Likelihood of Occurrence

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists

References

• Damkier P, Lassen D, Christensen MMH, Madsen KG, Hellfritzsch M, Pottegård A. Interaction between warfarin and cannabis. Basic Clin Pharmacol Toxicol. 2019;124(1):28-31.

Interaction Details

Warfarin is classified as belonging to the following category: Cytochrome P450 3A4 (Cyp3A4) Substrates

Theoretically, cannabis may increase the levels and adverse effects of CYP3A4 substrates.
In vitro research shows that cannabis can inhibit the activity of CYP3A4 enzymes, which might decrease the metabolism of CYP3A4 substrates.

Interaction Rating

Likelihood of Occurrence

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists

References

• Pellinen, P., Honkakoski, P., Stenback, F., Niemitz, M., Alhava, E., Pelkonen, O., Lang, M. A., and Pasanen, M. Cocaine N-demethylation and the metabolism-related hepatotoxicity can be prevented by cytochrome P450 3A inhibitors. Eur.J Pharmacol 1-3-1994;2

Interaction Details

Warfarin is classified as belonging to the following category: Anticoagulant/Antiplatelet Drugs

Theoretically, cannabis might increase the risk of bleeding when used concomitantly with anticoagulant/antiplatelet drugs.
In vitro research shows that the cannabis constituents delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) inhibit platelet aggregation.

Interaction Rating

Likelihood of Occurrence

Interaction has been documented in animal or in lab research, or the interaction has been documented in humans but is limited to case reports or conflicting clinical research exists

References

• Levy, R., Schurr, A., Nathan, I., Dvilanski, A., and Livne, A. Impairment of ADP-induced platelet aggregation by hashish components. Thromb.Haemost. 12-31-1976;36(3):634-640.
• Formukong, E. A., Evans, A. T., and Evans, F. J. The inhibitory effects of cannabinoids, the active constituents of Cannabis sativa L. on human and rabbit platelet aggregation. J.Pharm.Pharmacol. 1989;41(10):705-709.

Interaction Details

Warfarin is classified as belonging to the following category: Warfarin (Coumadin)

Concomitant use with cannabis seems to increase the levels and clinical effects of warfarin.
In vitro research shows that the cannabis constituents delta-9-tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabinol inhibit the cytochrome P450 2C9 (CYP2C9)-mediated 7-hydroxylation of S-warfarin in a concentration-dependent manner. There are also three case reports of patients chronically taking warfarin that developed a spike in international normalized ratio (INR) after smoking cannabis or taking medical cannabis orally. One of the patients smoked 2-2.5 grams in one week and another patient had doubled the amount of THC consumed from 7.5 mg to 14.7 mg daily for one week. The dose smoked by the third patient is unknown.

Interaction Rating

Likelihood of Occurrence

Interaction has not been documented in well-controlled studies, however, the interaction has been demonstrated in some small human studies or in controlled animal studies in conjunction with multiple case reports.

References

• Yamreudeewong W, Wong HK, Brausch LM, Pulley KR. Probable interaction between warfarin and marijuana smoking. Ann Pharmacother 2009;43:1347-53.
• Damkier P, Lassen D, Christensen MMH, Madsen KG, Hellfritzsch M, Pottegård A. Interaction between warfarin and cannabis. Basic Clin Pharmacol Toxicol. 2019;124(1):28-31.
• Brown GW, Bellnier TJ, Janda M, Miskowitz K. ?-9-tetrahydrocannabinol dose increase leads to warfarin drug interaction and elevated INR. J Am Pharm Assoc (2003). 2021;61(1):e57-e60.

Warfarin Overview

• Warfarin is used to prevent blood clots from forming or growing larger in your blood and blood vessels. It is prescribed for people with certain types of irregular heartbeat, people with prosthetic (replacement or mechanical) heart valves, and people who have suffered a heart attack. Warfarin is also used to treat or prevent venous thrombosis (swelling and blood clot in a vein) and pulmonary embolism (a blood clot in the lung). Warfarin is in a class of medications called anticoagulants ('blood thinners'). It works by decreasing the clotting ability of the blood.

Cannabis - More Interactions

Cannabis interacts with 1054 drugs

Interaction Rating Key

These severity listings are for informational use only. Never start, stop or otherwise change your therapy before speaking with your provider.