Predicted Net Effects of Drug-Gene Interactions on Levels of Tetrahydrocannabinol and Cannabidiol

Abstract Background: Circulating levels of THC and CBD may be altered when administered with medications that strongly or moderately inhibit or induce CYP450 enzymes responsible for metabolizing both substances. THC and CBD levels can also theoretically be altered in individuals who carry germline genetic variants or atypical phenotypes of CYP450 enzymes. In individuals where drug and gene interactions occur together, there could be a heightened impact on the circulating levels of THC and CBD. Materials and Methods: We conducted a retrospective chart review using a database of participants who previously completed pharmacogenomic testing and reported oral cannabis use in a medical encounter. Two pharmacogenomic-trained pharmacists reviewed medications and atypical variants in each participant to characterize the predicted effect of cannabis-drug, cannabis-gene, and cannabis-drug-gene interactions on circulating levels of THC and CBD. Results: Oral cannabis use was confirmed in 71 participants, with an average age of 68.5 years and primarily White women. Regarding THC metabolism, drug-only interactions were noted in 1 participant; both drug and gene interactions were noted in 4 participants; single- or combination-gene-only interactions were noted in 38 participants; and 28 participants had no interactions. Concerning CBD metabolism, drug-only interactions were noted in 4 participants; both drug and gene interactions were noted in 4 participants; single- or combination-gene-only interactions were noted in 36 participants; and 27 participants had no interactions. Conclusion: This study is the first, to our knowledge, to conceptualize the potential impact of drugs and atypical phenotypes on altering circulating levels of THC and CBD in a clinical sample. The absence of published clinical outcomes in this field renders it challenging to estimate clinical significance of these findings. Until such data become available, leveraging the theoretical insights into drug interactions and atypical cannabis metabolism described in our study may serve as a tool to guide clinical care.