A review of 665 screened articles identified potential interactions between cannabis and anticoagulants/antiplatelets, including THC increasing warfarin levels via CYP2C9 inhibition and CBD potentially reducing clopidogrel effectiveness via CYP2C19 inhibition.
Cardiologists, pharmacists, patients on blood thinners, and cannabis-using patients with cardiovascular conditions.
THC inhibits CYP2C9 (warfarin); CBD inhibits CYP2C19 (clopidogrel)
What the researchers found
Cannabis components can inhibit liver enzymes (CYP2C9, CYP2C19) and transporters involved in metabolizing blood thinners. Case reports showed cannabis inhibited warfarin metabolism, increasing INR and bleeding risk. CBD may reduce conversion of clopidogrel to its active form, potentially increasing stroke risk.
Why it matters
Patients using blood thinners for cardiac conditions, stroke prevention, or post-stent management are at high risk from drug interactions. With increasing medical and recreational cannabis use, clinicians need to be aware of these potential interactions.
The numbers in context
665 articles screened, 6 relevant publications identified. THC inhibits CYP2C9 (warfarin metabolism). CBD inhibits CYP2C19 (clopidogrel activation). Case reports documented increased INR with cannabis-warfarin co-use.
How the study worked
Review screening 665 articles from PubMed and EMBASE. Six relevant publications were identified: 4 case reports, 1 in vitro study, and 1 pharmacokinetic article.
What this study cannot tell us
Very limited direct evidence (only 6 relevant publications). Most data comes from case reports and in vitro studies. Clinical significance of these interactions in real-world dosing is not well established.
How to read the evidence
Moderate: plausible pharmacological mechanisms supported by case reports, but very limited clinical data.
When this study was published
Published in 2020 in Journal of Clinical Pharmacology.
The bigger picture
These interactions highlight a gap in patient counseling: patients on life-critical medications like warfarin or clopidogrel may not be asked about cannabis use, and cannabis users may not realize the risks of combining it with their prescribed medications.
Questions still open
- Should patients on blood thinners receive routine counseling about cannabis interactions? How clinically significant are these interactions at typical cannabis doses? Should INR monitoring be increased in warfarin patients who use cannabis?
Common questions
Can I use cannabis while taking blood thinners?
How strong is the evidence?
Read the original research
A Review of Cannabis and Interactions With Anticoagulant and Antiplatelet Agents.
Journal of clinical pharmacology, 60(4), 432-438
Citation
Greger, Jessica; Bates, Vernice; Mechtler, Laszlo; Gengo, Fran. (2020). A Review of Cannabis and Interactions With Anticoagulant and Antiplatelet Agents.. Journal of clinical pharmacology, 60(4), 432-438. https://doi.org/10.1002/jcph.1557
Explore the wider topic
- CBD Oil Quality Guide: How to Avoid Snake Oil
- Anxiety After Quitting Weed: When to Consider Medication
- Cannabis for Chemotherapy Nausea: What the Evidence Actually Shows
- Cannabis for Chronic Pain: What the Research Actually Supports
- Cannabis and Epilepsy: The Epidiolex Story and What It Means
- Does CBD Actually Work for Anxiety? What the Evidence Shows
- Does CBD Help with Weed Withdrawal? What Studies Show
- CBD vs THC: The Differences That Actually Matter
- The Proven Medical Benefits of Cannabis: What Research Supports
- Quitting Weed Before Surgery
- Weed and Medications: What Changes When You Quit
- Quitting Weed During Pregnancy: What You Need to Know
- Quitting Weed While Pregnant: What You Need to Know
- Cannabis and Older Adults: Risks Seniors Should Know
- Cannabis and Breastfeeding: THC in Breast Milk
- THC and Blood Pressure Medication: Cardiovascular Interactions
- THC and Caffeine: The Most Common Drug Combo on Earth