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

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.

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.

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.

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.

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).