Convergent Modifiers of Exposure Variability in Approved Cannabinoid Medicines: Pharmacogenomics, Drug–Drug Interactions, and Parent–Metabolite Divergence

Abstract

Background/Objectives: Systemic exposure to the approved cannabinoid medicines cannabidiol, nabiximols, dronabinol, and nabilone varies markedly among patients. Genotype and comedication may act at shared clearance steps and alter parent-drug and active-metabolite exposures differently. This review integrates pharmacogenomic, drug–drug interaction, and post-approval safety evidence within a convergent exposure-modifier (CEM) framework and develops testable hypotheses about their joint effects. Methods: A narrative, integrative review of bibliographic databases and regulatory documents for these medicines and key co-medications. Evidence was synthesized by pathway, product, analyte, interaction direction, directness, actionability, and limitations. Results: The framework distinguishes a victim branch, in which genotype and comedication modify cannabinoid exposure, from a perpetrator branch, in which cannabinoids alter co-medication exposure, with genotype potentially modifying it. Component evidence is strongest at CYP2C19 (cannabidiol–clobazam) and CYP2C9 (THC-containing medicines): cannabidiol increased N-desmethylclobazam exposure 3.4-fold in healthy volunteers while parent clobazam changed little, and CYP2C19 poor-metabolizer status independently increases baseline metabolite exposure. Comedication may phenoconvert genotype-predicted activity. No approved-product study identified in this review measured the joint genotype-by-comedication effect. Framework maturity is uneven: the predictions are cannabidiol-anchored; one relies on oral Δ9-THC evidence of unspecified formulation; nabiximols generates none, lacking genotype-stratified pharmacokinetics; and nabilone is excluded because its active-metabolite contributions are uncharacterized, although parent-drug activity is established. Conclusions: CEM is hypothesis-generating, not tested here: the three core predictions are falsifiable genotype-by-treatment tests requiring prospective validation. Label- and study-supported monitoring stands on its own evidence; the framework’s predictions do not, and genotype-guided dosing remains unvalidated.