Both THC and CBD can significantly alter how the body processes other medications — affecting absorption, metabolism, and elimination in ways that could make prescribed drugs more or less effective.
Pharmacists, clinicians prescribing to cannabis-using patients, anyone taking prescription medications alongside cannabis products.
What the researchers found
This review mapped the pharmacokinetic drug-drug interactions involving cannabinoids across the full ADME framework (absorption, distribution, metabolism, excretion).
The metabolism interactions are the most clinically significant. Both THC and CBD are metabolized by cytochrome P450 enzymes — the same enzyme family that processes the majority of prescription medications. CBD in particular is a potent inhibitor of several CYP450 enzymes (including CYP2C19, CYP2D6, and CYP3A4), meaning it can increase blood levels of co-administered drugs by blocking their breakdown.
This interaction is already documented clinically: CBD increases clobazam levels in epilepsy patients (leading to more sedation), and similar interactions are possible with antidepressants, antipsychotics, blood thinners, cardiovascular drugs, and opioids.
The review highlighted that as cannabis access increases, more patients will be combining cannabinoids with prescription medications — often without informing their healthcare providers. The resulting drug interactions may be misinterpreted as drug side effects, disease progression, or treatment failure.
Why it matters
Cannabis is increasingly used alongside prescription medications for pain, mental health, epilepsy, cancer, and cardiovascular conditions — exactly the categories where drug interactions could have serious consequences. This review provides a comprehensive interaction map that clinicians need as cannabis use normalizes among medicated populations.
The numbers in context
Key CYP450 enzymes affected: CYP2C19, CYP2D6, CYP3A4 (inhibited by CBD). Therapeutic areas with documented or potential interactions: pain medications, antidepressants, antipsychotics, anticoagulants, cardiovascular drugs, antiepileptics, opioids. CBD-clobazam interaction well-documented in epilepsy patients.
How the study worked
Narrative review examining pharmacokinetic drug-drug interactions involving cannabinoids. Covered interactions affecting absorption, distribution, metabolism, and excretion of co-administered medications. Focused on CYP450 enzyme interactions, drug transporter effects, and clinical case reports across multiple therapeutic areas.
Who was studied
Comprehensive review of cannabinoid interactions with various medications.
What this study cannot tell us
Many interaction predictions are based on in vitro (test tube) enzyme studies that may not translate directly to clinical significance. Cannabinoid products vary widely in composition, making it difficult to predict interactions from specific products. Most clinical interaction data come from pharmaceutical-grade CBD (Epidiolex) at high doses; recreational and medical cannabis products may have different interaction profiles.
How to read the evidence
Narrative review integrating in vitro enzyme data, clinical case reports, and pharmacokinetic studies — provides a comprehensive interaction map but significance of specific interactions varies.
When this study was published
Published in 2026 in the British Journal of Clinical Pharmacology, capturing interaction data as cannabis use increasingly overlaps with prescription medication populations.
The bigger picture
The CBD pharmacokinetics study (RTHC-00246) showed that food triples CBD absorption — and this review shows that higher CBD levels increase the interaction risk with other medications. The therapeutic cannabis review (RTHC-00250) noted that 27% of US adults have used cannabis medicinally, many while taking other medications. The cancer patient navigation study (RTHC-00262) found patients combining cannabis with cancer treatments without standardized guidance. Together, these studies describe a growing drug interaction problem that the healthcare system is poorly equipped to manage.
Replication
Not stated in abstract.
Funding
Not reported in abstract.
Conflicts of interest
Not reported in abstract.
Questions still open
- Should pharmacies routinely screen for cannabis use when dispensing medications known to interact with cannabinoids? At what CBD doses do clinically significant drug interactions become likely? Can pharmacogenomic testing identify patients most vulnerable to cannabinoid drug interactions?
Read the original research
Cannabinoids and drug-drug pharmacokinetic interactions: Deciphering the risks.
British journal of clinical pharmacology
The British Journal of Clinical Pharmacology is a well-respected journal focusing on the effects of drugs in humans.
Citation
Papakyriakopoulou, Paraskevi; Valsami, Georgia; Ismailos, Georgios. (2026). Cannabinoids and drug-drug pharmacokinetic interactions: Deciphering the risks.. British journal of clinical pharmacology. https://doi.org/10.1002/bcp.70430
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