12 Cannabinoids Tested Against 6 Liver Enzymes: CBD and THC Were the Strongest Inhibitors | Research

The takeaway

A comprehensive screen of 12 cannabinoids found that CBD and THC most potently inhibited the liver enzymes that process most medications, with several minor cannabinoids also showing significant effects.

Medical cannabis users on prescription medications, pharmacists, or doctors prescribing alongside cannabis.

12 × 6
Cannabinoids tested against drug-metabolizing enzymes — 72 interaction pairs mapped

What the researchers found

This was the most comprehensive cannabinoid-enzyme interaction study published to date. Researchers tested 12 different cannabinoids — including THC, CBD, CBN, CBG, CBC, THCV, and others — against 6 major drug-metabolizing CYP enzymes (CYP3A4, CYP2D6, CYP2C9, CYP1A2, CYP2B6, CYP2C19).

CBD emerged as the most potent inhibitor across multiple enzymes, consistent with previous reports. THC was also a significant inhibitor, particularly of CYP1A2 and CYP2C9. But the study's novel contribution was showing that so-called "minor" cannabinoids — CBN, CBG, and others present in full-spectrum cannabis products — also inhibited these enzymes at relevant concentrations.

This matters because full-spectrum cannabis products contain multiple cannabinoids simultaneously. The combined inhibitory load of several cannabinoids acting on the same enzymes could be greater than any single cannabinoid alone, creating unpredictable drug interactions.

Why it matters

Cannabis products are sold as isolates (pure CBD or THC) and as full-spectrum (containing multiple cannabinoids). This study showed that the full-spectrum products may carry additional drug interaction risk because minor cannabinoids also inhibit the same liver enzymes. Someone taking a full-spectrum CBD oil is exposed to a cocktail of enzyme inhibitors, not just one.

For the growing population of medical cannabis patients who are also on prescription medications — often multiple — this is clinically significant information that rarely appears on product labels.

The numbers in context

• 12 cannabinoids tested against 6 CYP enzymes (72 interaction pairs)

• CBD: most potent inhibitor across multiple enzymes

• THC: significant inhibitor of CYP1A2 and CYP2C9

• Minor cannabinoids (CBN, CBG, others) also showed inhibitory activity

• CYP3A4, CYP2D6, CYP2C9 — process the majority of prescription drugs

How the study worked

In vitro study using Supersomes (human CYP enzyme preparations) to screen 12 cannabinoids for inhibitory potential against CYP3A4, CYP2D6, CYP2C9, CYP1A2, CYP2B6, and CYP2C19. Used fluorometric probe substrates and IC50 determination. Published in The AAPS Journal.

Who was studied

Twelve cannabinoids assessed in vitro for their effects on drug metabolism.

What this study cannot tell us

In vitro study — enzyme inhibition in a test tube may not translate directly to clinical interactions in the body. Concentrations tested may not match what reaches the liver after typical cannabis use. Does not account for individual variation in enzyme expression or genetics. Cannot predict the combined effect of multiple cannabinoids acting simultaneously. No clinical validation included.

How to read the evidence

Rigorous in vitro pharmacology study with comprehensive cannabinoid coverage. Strong for identifying inhibitory potential, limited by lack of clinical correlation.

When this study was published

Published in 2021. Remains the most comprehensive cannabinoid-CYP enzyme interaction screen available.

The bigger picture

This study, alongside RTHC-00059 (THC interactions) and RTHC-00067 (CBD-SSRI interaction), completes a picture: cannabinoids as a class are significant inhibitors of drug-metabolizing enzymes. The clinical implications grow as cannabis use expands into older, sicker populations on multiple medications. The field is moving from "does cannabis interact with drugs?" (yes) to "which combinations are clinically dangerous?" (still being mapped).

Replication

Not stated in abstract.

Funding

Not reported in abstract.

Conflicts of interest

Not reported in abstract.

Questions still open

Do full-spectrum cannabis products pose greater drug interaction risk than isolates?
Should medical cannabis products be labeled with specific enzyme inhibition profiles?
At typical doses, which cannabinoid-drug combinations reach clinically significant interaction thresholds?

Common questions

Does full-spectrum CBD oil interact with medications differently than pure CBD?

Potentially yes. This study showed that minor cannabinoids (CBN, CBG, etc.) also inhibit liver enzymes, so full-spectrum products deliver multiple enzyme inhibitors simultaneously.

Which medications are most at risk for cannabis interactions?

Drugs processed by CYP3A4, CYP2D6, and CYP2C9 — which includes the majority of prescription medications. CBD was the most potent inhibitor across these enzymes.

Read the original research

Cannabinoid Interactions with Cytochrome P450 Drug Metabolism: a Full-Spectrum Characterization.

The AAPS journal, 23(4), 91

The AAPS Journal is a reputable peer-reviewed journal focusing on pharmaceutical sciences.

View on PubMed ↗Publisher’s paper ↗

Citation

Doohan, Peter T; Oldfield, Lachlan D; Arnold, Jonathon C; Anderson, Lyndsey L. (2021). Cannabinoid Interactions with Cytochrome P450 Drug Metabolism: a Full-Spectrum Characterization.. The AAPS journal, 23(4), 91. https://doi.org/10.1208/s12248-021-00616-7