CBD and THC Can Interfere With How Your Body Processes Other Medications | Research

The takeaway

A systematic review confirms CBD strongly inhibits key liver enzymes (CYP3A4, CYP2C9, CYP2C19) responsible for metabolizing about 80% of medications, raising important drug interaction concerns.

Anyone using CBD alongside other medications, pharmacists, prescribing clinicians, and cannabis-medicine researchers.

What the researchers found

CBD was consistently identified as a potent inhibitor of CYP3A4, CYP2C9, and CYP2C19 — enzymes that metabolize approximately 80% of therapeutic drugs. CYP2C19 could also be induced under certain conditions. CYP2D6 showed minimal or no modulation. THC also showed inhibitory effects but was less consistently studied.

Why it matters

With millions of people using CBD products alongside prescription medications, understanding drug interactions is critical for safety. The strong inhibition of CYP3A4 alone is clinically significant — this enzyme metabolizes drugs like blood thinners, statins, and anti-seizure medications.

The numbers in context

4 studies met inclusion criteria. CBD inhibited: CYP3A4, CYP2C9, CYP2C19. CYP2C19 also inducible in some conditions. CYP2D6: minimal/no effect. CYP450 enzymes metabolize ~80% of therapeutic drugs. Studies covered 2019-2025.

How the study worked

Systematic review per PRISMA guidelines searching PubMed, SciELO, ScienceDirect, and Scopus for studies published January 2019 to March 2025. Included in vitro, in vivo, and ex vivo studies evaluating phytocannabinoid effects on hepatic CYP450 isoforms. Four studies met eligibility criteria.

What this study cannot tell us

Only 4 studies met criteria, reflecting limited but growing research. Mostly in vitro data — clinical significance at typical CBD doses uncertain. THC less studied than CBD. Individual variation in CYP enzyme activity not captured.

How to read the evidence

Systematic review with consistent findings across studies, though only 4 studies met criteria and most are preclinical.

When this study was published

Published in 2026, reviewing the latest evidence on cannabinoid-drug interactions.

The bigger picture

As CBD becomes widely available over the counter, many users don't realize it can significantly alter how their body processes other medications. This review provides the scientific basis for why patients should inform healthcare providers about CBD use, especially if taking medications metabolized by CYP3A4.

Questions still open

At what CBD doses do clinically meaningful drug interactions occur? Should CBD products carry drug interaction warnings? How does chronic vs. acute CBD use affect enzyme inhibition?

Common questions

Can CBD interact with my medications?

Yes — CBD strongly inhibits liver enzymes responsible for processing about 80% of medications. This means CBD could cause other drugs to build up to higher-than-expected levels in your body, potentially increasing side effects. Always tell your doctor if you use CBD.

Which medications are most at risk?

Medications metabolized by CYP3A4, CYP2C9, and CYP2C19 are most affected. This includes many blood thinners (like warfarin), seizure medications, statins, and some antidepressants. A pharmacist can help identify if your specific medications are at risk.

Read the original research

The Influence of CBD and THC on Hepatic Enzymes of the Human Cytochrome P450 Complex Family: A Systematic Literature Review.

European journal of drug metabolism and pharmacokinetics, 51(1), 17-28

View on PubMed ↗Publisher’s paper ↗

Citation

Dos Santos, Mariana Candeias; da Silva, Anderson Matheus Pereira; da Vitória Santos do Nascimento, Maria; da Silva, Tânia Maria Sarmento; de Souza Franco, Eryvelton; de Sousa Maia, Maria Bernadete. (2026). The Influence of CBD and THC on Hepatic Enzymes of the Human Cytochrome P450 Complex Family: A Systematic Literature Review.. European journal of drug metabolism and pharmacokinetics, 51(1), 17-28. https://doi.org/10.1007/s13318-025-00978-9