Cannabis can interact with many common medications through shared liver enzymes and transporters | Research

The takeaway

A review of potential drug interactions found that cannabinoids can affect and be affected by the same liver enzymes and membrane transporters used by many prescription medications, warranting close monitoring in patients using both.

Read this if you use cannabis and take prescription medications and want to understand potential interactions.

Cannabinoids share metabolic pathways (CYP3A4, CYP2C9) with many common drugs

What the researchers found

Researchers reviewed the known and potential pharmacokinetic and pharmacodynamic interactions between cannabinoids and other medications. The review identified several key interaction pathways.

Cannabinoids are metabolized by cytochrome P450 enzymes (particularly CYP3A4, CYP2C9, and CYP2C19) and UDP-glucuronosyltransferases, the same enzyme systems that process many common medications. Both THC and CBD can inhibit or induce these enzymes, potentially raising or lowering blood levels of co-administered drugs.

Additionally, cannabinoids interact with membrane transporters including P-glycoprotein, breast cancer resistance proteins, and multidrug resistance proteins. These transporters affect how drugs are absorbed and distributed throughout the body.

The review noted that while cannabinoids are generally well tolerated, bidirectional interactions should be expected, meaning cannabinoids can change how other drugs work, and other drugs can change how cannabinoids work. This is particularly important for elderly patients, people with chronic diseases, and those with kidney or liver conditions.

Why it matters

As cannabis use expands legally and more patients combine it with prescription medications, understanding drug interactions becomes critical for safety. Many patients do not tell their doctors about cannabis use, and many doctors do not ask. This creates a blind spot where interactions could cause unexpected changes in drug efficacy or toxicity.

The numbers in context

Key CYP enzymes involved: CYP3A4, CYP2C9, CYP2C19. Key transporters: P-glycoprotein, breast cancer resistance proteins, multidrug resistance proteins. Key metabolic pathways: cytochrome P450 system, UDP-glucuronosyltransferases. Populations at highest risk: elderly, chronic disease patients, liver/kidney impairment.

How the study worked

This was a narrative review of published literature on cannabinoid pharmacokinetics, pharmacodynamics, and documented or potential drug interactions, with attention to the enzyme systems and transporters involved.

What this study cannot tell us

Many potential interactions identified in this review are theoretical, based on shared enzyme pathways rather than documented clinical events. In vitro enzyme inhibition data may not translate directly to clinically meaningful interactions at typical cannabis doses. The review does not quantify the likelihood or severity of specific interactions.

How to read the evidence

This is a narrative review synthesizing pharmacokinetic and pharmacodynamic data, providing moderate-level guidance based on known metabolic pathways.

When this study was published

Published in 2018. Drug interaction research for cannabis has continued to evolve with more clinical data.

The bigger picture

Drug interaction potential is one of the most practically important aspects of cannabis pharmacology. As medical cannabis gains legal status and self-medication with commercial cannabis products grows, the healthcare system needs better tools and awareness to identify and manage these interactions, particularly for the growing population of older adults using cannabis.

Questions still open

Which specific drug-cannabis interactions are clinically significant at typical use levels? Should cannabis users on multiple medications undergo therapeutic drug monitoring? How should pharmacists counsel patients about cannabis-medication interactions?

Common questions

Can cannabis change how my medications work?

Yes, potentially. Cannabis compounds are processed by the same liver enzymes (like CYP3A4) that metabolize many prescription drugs. This means cannabis could raise or lower blood levels of other medications. The risk is highest for people taking multiple medications, elderly patients, and those with liver or kidney conditions.

Should I tell my doctor I use cannabis?

This review strongly supports disclosing cannabis use to healthcare providers, particularly if you take prescription medications. The bidirectional nature of the interactions means both your cannabis effects and your medication effects could be altered.

Read the original research

Medicinal Cannabis-Potential Drug Interactions.

Medicines (Basel, Switzerland), 6(1)

View on PubMed ↗Publisher’s paper ↗

Citation

Alsherbiny, Muhammad A; Li, Chun Guang. (2018). Medicinal Cannabis-Potential Drug Interactions.. Medicines (Basel, Switzerland), 6(1). https://doi.org/10.3390/medicines6010003