THC, CBD, and CBN inhibit multiple drug-metabolizing enzymes, meaning cannabis products could alter the effectiveness or toxicity of many commonly prescribed medications.
Anyone taking medications alongside cannabis or CBD, pharmacists, and prescribing physicians.
THC, CBD, and CBN all inhibit CYP2C9, CYP1A1/2, and CYP1B1
What the researchers found
CYP2C9, CYP1A1/2, and CYP1B1 are likely inhibited by all three major cannabinoids (THC, CBD, CBN). CYP2D6, CYP2C19, CYP2B6, and CYP2J2 are inhibited by THC and CBD. CYP3A4/5/7 is potentially inhibited by CBD alone. Clinical evidence supports CBD inhibition of CYP2C19 and various cannabis products inhibiting CYP2C9.
Why it matters
As medical cannabis and CBD products proliferate, patients often take them alongside prescription medications. This review identifies specific enzyme pathways at risk, helping clinicians anticipate dangerous interactions.
The numbers in context
THC, CBD, and CBN all inhibit CYP2C9, CYP1A1/2, CYP1B1. THC and CBD inhibit CYP2D6, CYP2C19, CYP2B6, CYP2J2. CBD inhibits CYP3A4/5/7, UGT1A9, and potentially CES1. Cannabis smoking induces CYP1A2.
How the study worked
Systematic literature search of Google Scholar and PubMed through March 2019 for in vitro and clinical studies of cannabis drug interaction potential. In vitro inhibition parameters were compared to physiologically achievable cannabinoid concentrations.
What this study cannot tell us
Many findings are based on in vitro data that may not reflect real-world clinical significance. Clinical drug interaction studies with cannabis are still limited. Most in vivo data involves smoked cannabis or CBD specifically.
How to read the evidence
Moderate: systematic review combining in vitro and limited clinical data, providing comprehensive but partly theoretical interaction profiles.
When this study was published
Published in 2019.
The bigger picture
The explosion of CBD products means millions of people are unknowingly combining cannabinoids with medications metabolized by the same enzymes. Warfarin (CYP2C9), clopidogrel (CYP2C19), and many psychiatric drugs (CYP2D6) could all be affected.
Questions still open
- At what doses do cannabis-drug interactions become clinically significant? Should patients on blood thinners avoid cannabis entirely? Do different consumption methods change the interaction profile?
Common questions
Which medications are most at risk?
Does this apply to CBD products sold in stores?
Read the original research
The Potential for Pharmacokinetic Interactions Between Cannabis Products and Conventional Medications.
Journal of clinical psychopharmacology, 39(5), 462-471
Citation
Qian, Yuli; Gurley, Bill J; Markowitz, John S. (2019). The Potential for Pharmacokinetic Interactions Between Cannabis Products and Conventional Medications.. Journal of clinical psychopharmacology, 39(5), 462-471. https://doi.org/10.1097/JCP.0000000000001089
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