Cannabinoids interact with a wide range of medications through CYP450 enzyme inhibition and other mechanisms — this review maps the specific interactions relevant to epilepsy, autism, cancer, MS, and chronic pain treatments.
Read this if you use medical cannabis alongside prescription medications for epilepsy, cancer, pain, or other serious conditions — or if you're a clinician managing these patients.
What the researchers found
As medical cannabis use expands, patients are increasingly combining cannabinoids with prescription medications for serious conditions. This review maps out the drug interaction landscape across five major therapeutic areas where cannabinoid use is common: epilepsy, autism spectrum disorder, cancer, multiple sclerosis, and chronic pain.
The interactions work through several mechanisms. The most common is inhibition of cytochrome P450 (CYP) enzymes, the liver's main drug-processing system. Both THC and CBD inhibit CYP2C9 and CYP3A4 — two enzymes that collectively metabolize a large proportion of prescription drugs. When these enzymes are inhibited, co-administered medications accumulate to higher blood levels, potentially causing toxicity.
Specific examples highlight the clinical significance. The antifungal ketoconazole (a CYP3A4 inhibitor itself) increases plasma concentrations of both THC and CBD when taken together. Conversely, rifampicin (a CYP3A4 inducer, used for tuberculosis) reduces THC levels by 20-40% and CBD levels by 50-60%, potentially making cannabis treatment ineffective.
For epilepsy patients on clobazam — one of the most common co-prescribed drugs with CBD — the interaction is particularly important: CBD inhibits CYP2C19, causing clobazam levels to rise significantly, which can increase sedation and requires dose adjustment. In cancer treatment, cannabinoid interactions with chemotherapy agents could either reduce efficacy or increase toxicity.
The review emphasizes that interactions can be additive, synergistic, or antagonistic — and may affect absorption, distribution, metabolism, and excretion. The bottom line: cannabinoids are pharmacologically active drugs that interact with the body's drug processing systems in clinically meaningful ways.
Why it matters
Patients using medical cannabis for serious conditions are often on multiple other medications. This review provides a practical reference for the specific interaction risks in the conditions where cannabinoid use is most common. The clinical stakes are high: in epilepsy, interactions could cause breakthrough seizures or excessive sedation; in cancer, they could affect chemotherapy efficacy; in pain management, they could cause opioid accumulation.
The numbers in context
Ketoconazole increases plasma THC and CBD concentrations (CYP3A4 inhibition). Rifampicin reduces THC levels by 20-40% and CBD by 50-60% (CYP3A4 induction). CBD inhibits CYP2C9 and CYP3A4, affecting metabolism of warfarin, some chemotherapy agents, opioids, and anticonvulsants. Clobazam-CBD interaction (via CYP2C19) is clinically documented and requires dose adjustment.
How the study worked
Narrative review critically summarizing published evidence on drug-cannabinoid interactions across five therapeutic areas: epilepsy, autism spectrum disorder, cancer, multiple sclerosis, and chronic pain. Focused on CYP450-mediated interactions, pharmacodynamic interactions, and clinical consequences.
Who was studied
Review of drug interactions involving cannabinoids and various therapeutic agents.
What this study cannot tell us
Narrative review, not systematic. Drug interaction evidence varies greatly in quality — some interactions are based on controlled human studies, others on case reports or in vitro data only. Individual patient factors (genetics, liver function, dose, other medications) affect actual interaction risk. The review covers five therapeutic areas but not all medications within those areas. Cannabis product variability (different THC:CBD ratios, other cannabinoids) means interaction risk differs between products.
How to read the evidence
Narrative review synthesizing evidence from controlled trials, case reports, and in vitro studies. Evidence quality varies by specific interaction. The CYP450 mechanism is well-established; specific clinical consequences are better documented for some drug pairs than others.
When this study was published
Published in 2024. Drug interaction research for cannabinoids is expanding rapidly as more patients combine cannabis with conventional medications.
The bigger picture
This is the broadest drug interaction review in the database, tying together the specific findings from RTHC-00091 (controlled CYP450 human trial), RTHC-00104 (blood thinner interactions), and RTHC-00078 (buprenorphine interaction). While those studies demonstrated individual interactions, this review maps the full landscape. The message is consistent: cannabinoids are real drugs with real pharmacokinetic interactions, and patients combining them with other medications need monitoring.
Replication
Not stated in abstract.
Funding
Not reported in abstract.
Conflicts of interest
Not reported in abstract.
Questions still open
- Should pharmacies and dispensaries have interaction-checking systems for cannabinoids, similar to those for prescription drugs? At what CBD/THC doses do clinically meaningful interactions begin? Should patients starting medical cannabis have their co-prescribed medication levels monitored more frequently? Could standardized cannabinoid products reduce interaction variability compared to whole-plant products?
Read the original research
Drug-Cannabinoid Interactions in Selected Therapeutics for Symptoms Associated with Epilepsy, Autism Spectrum Disorder, Cancer, Multiple Sclerosis, and Pain.
Pharmaceuticals (Basel, Switzerland), 17(5)
Pharmaceuticals is a peer-reviewed journal focusing on drug development and therapeutic applications.
Citation
Campos, Maria G; China, Maria; Cláudio, Mariana; Capinha, Miguel; Torres, Rita; Oliveira, Simão; Fortuna, Ana. (2024). Drug-Cannabinoid Interactions in Selected Therapeutics for Symptoms Associated with Epilepsy, Autism Spectrum Disorder, Cancer, Multiple Sclerosis, and Pain.. Pharmaceuticals (Basel, Switzerland), 17(5). https://doi.org/10.3390/ph17050613
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