First Crystal Structures Show How THC Fits Inside the Body's Main Drug-Metabolizing Enzyme | Research

The takeaway

X-ray crystallography revealed exactly how THC binds inside CYP3A4, the enzyme responsible for metabolizing most medications, providing a structural basis for predicting cannabinoid-drug interactions.

Pharmacologists, medicinal chemists, and clinicians concerned about cannabinoid-drug interactions.

What the researchers found

THC and CBD act as type I ligands causing a nearly complete high-spin transition in CYP3A4 (Kd of 1.9 and 3.6 micromolar respectively), while cannabinol caused negligible changes. Crystal structures showed THC positions its cyclohexenyl C7/C8 atoms (main metabolic sites) toward the heme center. THC binding is driven by hydrophobic interactions rather than the polar interactions critical for other drugs.

Why it matters

CYP3A4 metabolizes roughly half of all prescription medications. Understanding at the atomic level how cannabinoids interact with this enzyme is essential for predicting drug interactions, which is increasingly important as cannabis use rises alongside prescription medication use.

The numbers in context

THC Kd: 1.9 micromolar. CBD Kd: 3.6 micromolar. Cannabinol: negligible spectral changes. THC uses hydrophobic binding; darifenacin uses hydrogen bonding to S119. THC approaches heme at C7/C8 metabolic sites.

How the study worked

Spectral analysis, site-directed mutagenesis, and X-ray crystallography were used to characterize how CYP3A4 interacts with THC, CBD, cannabinol, and the comparator drug darifenacin. Crystal structures of productive CYP3A4-THC complexes were solved.

What this study cannot tell us

Crystal structures represent static snapshots that may not capture the dynamic nature of enzyme-substrate interactions. In vitro binding does not predict in vivo metabolic outcomes. Human CYP3A4 activity is influenced by many factors not captured in crystallography (other enzymes, membrane environment, genetic variants).

How to read the evidence

High-resolution structural data with mutagenesis validation, but in vitro system does not capture the full complexity of in vivo drug metabolism.

When this study was published

Published 2025.

The bigger picture

With over 30% of U.S. adults having tried CBD and millions using prescription medications metabolized by CYP3A4, the potential for cannabinoid-drug interactions is enormous. These crystal structures provide the structural foundation for computational modeling of interaction risks with specific medications.

Questions still open

Whether THC's binding to CYP3A4 at 1.9 micromolar Kd is strong enough to cause clinically meaningful drug interactions at typical cannabis use levels
How the structural differences between THC and CBD binding to CYP3A4 affect their respective drug interaction profiles

Common questions

Could cannabis interfere with my medications?

This study shows THC binds tightly to CYP3A4, which metabolizes about half of all prescription drugs. This means THC could theoretically slow the breakdown of many medications, potentially increasing their blood levels and side effects. The clinical significance depends on cannabis dose and the specific medication.

Why did cannabinol behave differently than THC and CBD?

Cannabinol caused negligible changes in CYP3A4, suggesting it interacts very weakly with the enzyme. This means CBN-containing products may have a different drug interaction profile than THC or CBD products, though more research is needed.

Read the original research

Interaction of cytochrome P450 3A4 with cannabinoids and the drug darifenacin.

The Journal of biological chemistry, 301(10), 110709

View on PubMed ↗Publisher’s paper ↗

Citation

Sevrioukova, Irina F. (2025). Interaction of cytochrome P450 3A4 with cannabinoids and the drug darifenacin.. The Journal of biological chemistry, 301(10), 110709. https://doi.org/10.1016/j.jbc.2025.110709