Drug & supplement interaction

Cannabis + Warfarin Sodium

Warfarin Sodium brand names: Coumadin, Panwarfin, Sofarin.

Major Interaction
Medically reviewed by · Updated September 2026
The bottom line Major

Warfarin Sodium falls into 5 drug categories that Cannabis can interact with; the most serious is rated major. Concomitant use with cannabis seems to increase the levels and clinical effects of warfarin.

Read the full interaction report
SeverityMajor
LikelihoodProbable
Interactions5
EvidenceD
What do Severity, Likelihood & Evidence mean?
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Interaction report

Cannabis and Warfarin Sodium

These two interact in 5 distinct ways. Each one is explained separately below.

Why Are There 5 Interactions?

Cannabis interacts with whole categories of medication. Warfarin Sodium falls into 5 of those categories, so it can interact with Cannabis in 5 different ways. We’ve listed each one below — your overall risk is driven by the most serious of them (Major).

Major

WARFARIN (Coumadin)

1 of 5
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.
Additionally, there are multiple case reports of patients chronically taking warfarin that developed a spike in international normalized ratio (INR) after using cannabis in various forms, including smoking cannabis, taking medical cannabis orally, or drinking water infused with cannabis flower. One patient 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.
Severity Major Likelihood Probable Evidence D

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..

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist: your liver uses an enzyme called CYP2C9 to break down warfarin and keep its blood-thinning effect steady. Compounds in cannabis (THC and CBD) appear to slow that enzyme down. When warfarin clears more slowly, it can build up, which means more blood-thinning than intended. In practice that shows up as a higher INR on your blood test and a greater risk of bruising or bleeding, like nosebleeds, bleeding gums, or blood in your urine or stool.

Warfarin is a narrow-therapeutic-index drug, so even small shifts matter. The evidence here is mostly lab data plus a handful of patient case reports, not large studies, but the cases are real enough to take seriously. If you use cannabis in any form, please tell your doctor or pharmacist so your INR can be watched. Don't change anything on your own.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Yamreudeewong W, Wong HK, Brausch LM, Pulley KR. Probable interaction between warfarin and marijuana smoking. Ann Pharmacother 2009;43:1347-53. PubMed
  2. 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. PubMed
  3. 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. PubMed
  4. Udomuksorn W, Saowaneepitak N, Dolthammasiri P, et al. Unveiling the impact of water-boiled cannabis on warfarin: A case report of atrial fibrillation patients after cannabis legalization in Thailand. Toxicol Rep 2024;13:101838. PubMed
Moderate

CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES

2 of 5

Why this applies to Warfarin Sodium

Warfarin Sodium falls under CYTOCHROME P450 2C9 (CYP2C9) SUBSTRATES — the group Cannabis interacts with.

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. In vitro research also shows that cannabis extracts modestly inhibit the CYP2C9 metabolism of tolbutamide; extracts providing the specific cannabinoids CBD and cannabigerol (CBG) had stronger inhibitory effects than extracts containing THC and CBD.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist with warfarin and cannabis. Your liver uses an enzyme called CYP2C9 to clear out the active part of warfarin. Lab studies suggest that cannabis compounds (THC, CBD, and cannabinol) can slow that enzyme down a bit. If warfarin gets cleared more slowly, it can build up, and that means your blood may get thinner than intended.

Because warfarin is a narrow therapeutic index drug, even small shifts matter. Too much effect can show up as easy bruising, nosebleeds, bleeding gums, or blood in urine or stool. Keep in mind this concern comes mostly from test-tube research, not solid human studies, so it's a theoretical caution. Still, please loop in your doctor or pharmacist before adding cannabis, since your INR may need closer watching.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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. PubMed
  2. Treyer A, Reinhardt JK, Eigenmann DE, Oufir M, Hamburger M. Phytochemical comparison of medicinal cannabis extracts and study of their CYP-mediated interactions with coumarinic oral anticoagulants. Med Cannabis Cannabinoids. 2023;6(1):21-31. PubMed
Moderate

CYTOCHROME P450 3A4 (CYP3A4) SUBSTRATES

3 of 5

Warfarin Sodium also falls under 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. In vitro research also shows that cannabis extracts modestly inhibit the CYP3A4 metabolism of testosterone; extracts providing the specific cannabinoids CBD and cannabigerol (CBG) had stronger inhibitory effects than extracts containing THC and CBD.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist with warfarin and cannabis. Warfarin is partly broken down by a liver enzyme called CYP3A4. Lab studies suggest cannabis compounds (especially CBD and CBG) can slow that enzyme down. If your body clears warfarin a little slower, more of it can hang around, which could nudge your blood toward being too thin. That can show up as easy bruising, nosebleeds, bleeding gums, or, less commonly, more serious bleeding.

I want to be honest about the evidence: this is mostly theoretical, based on test-tube work, not strong human studies. But warfarin is a narrow-window drug where small shifts matter. If you use or are considering cannabis, please loop in your doctor or pharmacist so your INR can be watched closely.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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 PubMed
  2. Treyer A, Reinhardt JK, Eigenmann DE, Oufir M, Hamburger M. Phytochemical comparison of medicinal cannabis extracts and study of their CYP-mediated interactions with coumarinic oral anticoagulants. Med Cannabis Cannabinoids. 2023;6(1):21-31. PubMed
Moderate

ANTICOAGULANT/ANTIPLATELET DRUGS

4 of 5

Warfarin Sodium also falls under 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.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist if you take warfarin (Coumadin) and are thinking about cannabis. Warfarin is a blood thinner with a very narrow safety window, so even small shifts in how your blood clots can matter. Lab studies suggest that cannabis compounds (THC and CBD) may make platelets a little less sticky, which in theory could add to warfarin's clot-preventing effect and slightly raise your bleeding risk.

I want to be honest about the evidence: this is theoretical, based on test-tube research, not strong human studies. Still, with warfarin I always play it safe. Watch for easy bruising, nosebleeds, bleeding gums, or dark stools, and keep your INR checks on schedule. Please don't start or stop anything on your own. Loop in your doctor or pharmacist first.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. 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. DOI
  2. 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.
Moderate

CYTOCHROME P450 2C19 (CYP2C19) SUBSTRATES

5 of 5

Warfarin Sodium also falls under CYTOCHROME P450 2C19 (CYP2C19) SUBSTRATES.

Cannabis may increase levels of drugs metabolized by CYP2C19.
Research shows that cannabidiol (CBD), a constituent of cannabis, inhibits CYP2C19. In clinical studies and case reports, cannabidiol use resulted in significant increases in the serum levels of topiramate, methadone, citalopram, omeprazole, and N-desmethylclobazam, the primary active metabolite of clobazam. These chemicals are metabolized by CYP2C19. Concomitant use of cannabis with CYP2C19 substrates may increase the risk for adverse effects from these substrates.
Severity Moderate Likelihood Possible Evidence D

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.

Dr. Brian Staiger, PharmD, BCPS
Dr. Brian Staiger explains PharmD, Clinical Pharmacist

Here's the gist for warfarin. The CBD in cannabis can slow down a liver enzyme called CYP2C19, which is one of the pathways your body uses to break down warfarin. If that pathway slows, more active warfarin can hang around, and your blood may end up thinner than intended. In real terms, that can show up as a rising INR, easy bruising, nosebleeds, or bleeding that's harder to stop.

Warfarin is a narrow-margin drug, so even small shifts matter. This particular interaction is mostly theoretical and based on how the drugs work, not hard warfarin studies, so I don't want to alarm you. Just please loop in your doctor or pharmacist before mixing them, and don't change your dose on your own. They may simply want to check your INR a bit more closely.

Contact Dr. Brian directly if you have additional questions on this interaction
References
  1. Harvey DJ. Absorption, distribution, and biotransformation of the cannabinoids. Marijuana and Medicine. 1999;91-103. DOI
  2. Bornheim LM, Everhart ET, Li J, Correia MA. Characterization of cannabidiol-mediated cytochrome P450 inactivation. Biochem Pharmacol 1993;45(6):1323-31. PubMed
  3. Gaston TE, Bebin EM, Cutter GR, Liu Y, Szaflarski JP; UAB CBD Program. Interactions between cannabidiol and commonly used antiepileptic drugs. Epilepsia. 2017 Sep;58(9):1586-92. PubMed
  4. Devinsky O, Marsh E, Friedman D, et la. Cannabidiol in patients with treatment-resistant epilepsy: an open-label interventional trial. Lancet Neurol. 2016 Mar;15(3):270-8.
  5. Geffrey AL, Pollack SF, Bruno PL, Thiele EA. Drug-drug interaction between clobazam and cannabidiol in children with refractory epilepsy. Epilepsia. 2015 Aug;56(8):1246-51. PubMed
  6. Madden K, Tanco K, Bruera E. Clinically Significant Drug-Drug Interaction Between Methadone and Cannabidiol. Pediatrics. 2020;e20193256. PubMed
  7. Anderson LL, Doohan PT, Oldfield L, et al. Citalopram and Cannabidiol: In Vitro and In Vivo Evidence of Pharmacokinetic Interactions Relevant to the Treatment of Anxiety Disorders in Young People. J Clin Psychopharmacol. 2021. PubMed
  8. Nasrin S, Watson CJW, Perez-Paramo YX, Lazarus P. Cannabinoid Metabolites as Inhibitors of Major Hepatic CYP450 Enzymes, with Implications for Cannabis-Drug Interactions. Drug Metab Dispos 2021;49(12):1070-1080. PubMed
  9. Bansal S, Zamarripa CA, Spindle TR, et al. Evaluation of Cytochrome P450-Mediated Cannabinoid-Drug Interactions in Healthy Adult Participants. Clin Pharmacol Ther 2023.

What These Ratings Mean

Every interaction above is graded three ways — here’s the key to each label.

Severity how clinically significant the interaction is
Major

Clinically significant. Avoid the combination, or use only under close professional supervision.

Moderate

Usually worth avoiding or managing — may need monitoring, a dose change, or timing apart.

Minor

Generally not serious. Be aware of it and mention it to your pharmacist.

Likelihood how strong the evidence is that the interaction actually happens in people
  • LikelyWell-controlled human studies have demonstrated the likely existence of this interaction.
  • ProbableInteraction 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.
  • PossibleInteraction 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.
  • UnlikelyInteraction has been demonstrated in animal or in lab research but has been shown not to occur in humans.
Evidence the quality of the studies behind the rating (graded A–D)
  • AHigh-quality meta-analysis (quantitative systematic review).
  • BCase-control study.
  • CConsensus.
  • DAnecdotal evidence.

These ratings are for information only. Never start, stop, or otherwise change your therapy before speaking with your provider.

Keep it in perspective

Cannabis Also Interacts With Other Medications

Cannabis has 1 major, 1,109 moderate, 25 minor known drug interactions in our database — the Warfarin Sodium one above is among them. If you take anything else, check it against the full list below.

Major 1 Moderate 1,109 Minor 25 No known interaction 1,695 (incl. Warfarin Sodium)
Taking anything else?

Check Another of Your Medications Against Cannabis

Covers the 2,830 medications we’ve checked against Cannabis. Pick one to open its full report.

From our Q&A

Questions About Cannabis or Warfarin Sodium

These are real questions from readers, answered by the pharmacists at HelloPharmacist — written by a person, not generated from a database. Each one covers Cannabis or Warfarin Sodium, not necessarily both, but if one is close to what you were about to ask it will usually go further than a database entry can:

Not quite your question? Ask our pharmacists directly — it is free, there is no account required, and answers usually come back within 24 hours.

Everything else you take

See Every Supplement That Interacts With Warfarin Sodium

This page covers Cannabis only. If you take other supplements — a multivitamin, a sleep aid, something for joints — the Warfarin Sodium page lists 361 supplements it has a documented interaction with, worst first, each one explained.

The most serious there right now: Activated Charcoal (major), Alfalfa (major), American Ginseng (major), Beer (major) and Danshen (major).

Open the Warfarin Sodium interaction page

One more smart check

Taking Cannabis as Part of a Dietary Supplement Product? Check It for Interactions

We hold 21 real supplement products containing Cannabis, each one broken down to its full ingredient list — and combination products often carry several ingredients besides Cannabis. Your product may carry other ingredients that interact with Warfarin Sodium too, on top of Cannabis — and those would not show on this page. Find your product and we’ll check every ingredient on its label:

How much people look this up

Where Cannabis and Warfarin Sodium Sit Against Everything Else

Out of every supplement and medication people look up on HelloPharmacist, here is where these two land this week — and which way each has been moving.

Supplement Cannabis
Top 25%

#203 of 1,452 supplements looked up here in the last 7 days

29 days ago today
Medication Warfarin Sodium
Top 1%

#25 of 2,830 medications looked up here in the last 7 days

29 days ago today

Position among everything looked up on this site, not a measure of how commonly either one is used or how important it is. A supplement can climb this list because of a news story. It counts every request to the page, automated ones included, and nothing here identifies anyone.

Supplement

About Cannabis

What is Cannabis?

Cannabis
  • Chronic pain
  • Nausea and vomiting from chemotherapy
  • Muscle spasticity (e.g., multiple sclerosis)
  • Anxiety and stress
  • Sleep problems
  • Appetite stimulation

Cannabis contains many active compounds, mainly THC (which causes a 'high') and CBD (which does not). Some uses, such as chemotherapy-related nausea, certain seizure disorders, and muscle spasticity, have meaningful evidence, while many other popular uses are not well proven. It can cause real side effects and impairment, so talk to your doctor or pharmacist and follow your local laws before using it.

Read the full Cannabis monograph & all interactions
Medication

About Warfarin

What Is Warfarin Used For?

Brand names: Coumadin, Panwarfin, Sofarin

Warfarin sodium tablets and Jantoven tablets are both used to prevent and treat venous thrombosis (blood clots in the veins) and pulmonary embolism (a clot in the lungs). They are also used to prevent clot-related complications in people with atrial fibrillation (an irregular heart rhythm) or who have had a heart valve replaced.

In people who have had a heart attack, warfarin is used to reduce the risk of death, another heart attack, stroke, or other clotting events. It does not dissolve an existing clot, but it helps prevent the clot from growing and stops new dangerous clots from forming.

See full Warfarin drug information
Keep checking

Other Drugs & Cannabis

Browse every other medication we’ve checked against Cannabis — both the ones with a known interaction and the ones without. Select any drug for the full detail.

1Major
1,109Moderate
25Minor
1,694No known interaction
1 Major 1,109 Moderate 25 Minor 1,694 No interaction
Major

1 interaction

Moderate

1,109 interactions

Showing 60 of 1,109 moderate interactions — see all 1,109 on the Cannabis page.

Minor

25 interactions

No interaction 1,694 drugs checked — show the list

We also checked Cannabis against these medications and found no known interaction in our sources. Open any page to confirm.

Showing the 60 most looked-up of 1,694 medications checked with no known interaction — see the full Cannabis list.

See the full Cannabis interactions page
See every supplement checked against Warfarin Sodium, ranked by severity
Sources

Sources & How We Checked

Interaction details are evidence-graded and sourced from the Natural Medicines database. The medication overview comes from MedlinePlus.

Content is written and reviewed by licensed HelloPharmacist pharmacists. See our data sources and editorial standards for how this information is built and checked.

Parts of this content are provided by the Therapeutic Research Center, LLC.

DISCLAIMER: Currently this does not check for drug-drug interactions. This is not an all-inclusive comprehensive list of potential interactions and is for informational purposes only. Not all interactions are known or well-reported in the scientific literature, and new interactions are continually being reported. Input is needed from a qualified healthcare provider including a pharmacist before starting any therapy. Application of clinical judgment is necessary.

© 2021 Therapeutic Research Center, LLC

Keep exploring
Cannabis monograph › Uses, safety, and every drug interaction in one place Warfarin Sodium supplement interactions › Every supplement checked against Warfarin Sodium, ranked by severity Warfarin drug information › The full plain-English guide to this medication Supplement interaction checker › Check any supplement or product against your medications Browse medications A–Z › Every drug we've checked against herbs & supplements Ask a pharmacist › Free, personal answer from our licensed team
Pharmacist Counseling Corner

Taking Cannabis and Warfarin Sodium Together: Common Questions

Can you take Cannabis with Warfarin Sodium?
This is rated a major interaction, so the combination is best avoided unless your doctor or pharmacist has specifically told you otherwise. Read the full details on this page and confirm with your pharmacist before combining them.
Why are there 5 interactions listed for Cannabis and Warfarin Sodium?
Warfarin Sodium belongs to more than one drug category, and Cannabis interacts with each of those categories a little differently. We list every one so nothing is missed — your overall risk is driven by the most serious of them.
How serious is the Cannabis and Warfarin Sodium interaction?
We rate it Major. This is a clinically significant combination that is generally best avoided, or used only under the direct supervision of your physician or pharmacist.

Written and reviewed by the HelloPharmacist editorial staff. Our editorial policy

Still Have a Question About Warfarin Sodium and Cannabis?

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This information is for education only and is not a substitute for professional medical advice. Always check with your pharmacist or doctor before starting, stopping, or combining supplements and medications.