How Cannabis, Tobacco, and Smoking Cessation Products Interact With Other Medications | Research

The takeaway

Cannabis and tobacco smoke both induce the CYP1A2 enzyme (additively), potentially affecting drug levels, while THC and CBD are primarily metabolized by CYP3A4, and CBD may significantly inhibit CYP2C19.

Anyone using cannabis alongside prescription medications, and clinicians managing patients who use cannabis.

Cannabis and tobacco smoke additively induce CYP1A2, affecting metabolism of many medications

What the researchers found

This pharmacokinetics review examined how tobacco smoking, cannabis use, and smoking cessation products interact with medications metabolized by liver enzymes.

Both marijuana and tobacco smoke induce the CYP1A2 enzyme through the same pathway (aromatic hydrocarbon receptor), and the effect is additive when both are smoked. When someone stops smoking, CYP1A2 activity drops quickly, potentially causing toxicity from medications that were previously metabolized at a faster rate.

For cannabis specifically, CYP3A4 appears to be the primary enzyme metabolizing both THC and CBD, meaning drugs that induce or inhibit CYP3A4 can significantly alter cannabinoid levels. Limited data also suggest CBD may inhibit CYP2C19, which could affect a range of medications metabolized by that enzyme.

Why it matters

As cannabis use increases, understanding how it interacts with prescription medications becomes critical for patient safety. The CYP1A2 induction from smoking cannabis could alter levels of drugs like clozapine, theophylline, and caffeine, while CBD's potential CYP2C19 inhibition could affect drugs like clopidogrel and certain antidepressants.

The numbers in context

Both cannabis and tobacco smoking induce CYP1A2 (additive effect). CYP3A4 is the primary metabolic pathway for THC and CBD. CBD may significantly inhibit CYP2C19. Nicotine metabolism by CYP2A6 is induced by estrogen, resulting in lower nicotine levels in females, especially those on oral contraceptives.

How the study worked

This was a comprehensive review of pharmacokinetic data on drug interactions involving tobacco smoke, cannabis, and smoking cessation products, published in a clinical pharmacokinetics journal.

What this study cannot tell us

The review noted limited data on many cannabis-drug interactions, particularly for smoked cannabis versus pharmaceutical cannabinoid products. Most interaction data come from in-vitro studies or pharmaceutical cannabinoid preparations rather than whole-plant cannabis. Clinical studies are needed to determine real-world significance of many theoretical interactions.

How to read the evidence

This is a comprehensive pharmacokinetics review drawing on clinical and in-vitro data. While the enzyme interactions are well-characterized, clinical significance of many interactions remains to be fully determined.

When this study was published

Published in 2016. Understanding of cannabis-drug interactions has continued to develop, particularly with the rise of CBD products.

The bigger picture

Drug interactions with cannabis are an underappreciated safety concern. As more patients use cannabis alongside prescription medications, understanding these pharmacokinetic interactions is essential for dosing adjustments and avoiding adverse effects.

Questions still open

How does the route of cannabis administration (smoked vs. oral vs. vaporized) affect drug interaction profiles? Which commonly prescribed medications are most affected by cannabis co-use?

Common questions

Can cannabis affect how my medications work?

Yes. Cannabis smoke induces the CYP1A2 enzyme, which can lower levels of certain medications. THC and CBD are metabolized by CYP3A4, so drugs affecting this enzyme can alter cannabinoid levels. CBD may also inhibit CYP2C19, potentially raising levels of drugs metabolized by that pathway.

Should I worry about drug interactions if I stop smoking cannabis?

Stopping smoking (cannabis or tobacco) causes CYP1A2 to decrease rapidly. If you are on medications metabolized by CYP1A2, their levels may rise after you stop smoking, potentially requiring dose adjustments. This is most important for drugs with narrow therapeutic windows.

Read the original research

Pharmacokinetic Drug Interactions with Tobacco, Cannabinoids and Smoking Cessation Products.

Clinical pharmacokinetics, 55(11), 1353-1368

View on PubMed ↗

Citation

Anderson, Gail D; Chan, Lingtak-Neander. (2016). Pharmacokinetic Drug Interactions with Tobacco, Cannabinoids and Smoking Cessation Products.. Clinical pharmacokinetics, 55(11), 1353-1368.