The availability of cannabis for recreational and medical use has increased substantially, making it the most widely used drug worldwide and the most frequently detected substance in road traffic controls. Genetic variations in cannabinoid-metabolizing enzymes are relevant but remain understudied. Specifically, their impact on whole-blood concentrations of Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD), and their metabolites is not fully understood and has not been systematically evaluated in driving-under-the-influence-of-drugs (DUID) cases. Therefore, this study assessed the impact of genetic variation in cannabinoid-metabolizing cytochrome P450 (CYP) enzymes on blood cannabinoid concentrations following controlled inhalation of legally available cannabis products, with relevance to road traffic controls.

In 2019, the Institute of Forensic Medicine Basel conducted a controlled clinical trial to assess blood cannabinoid concentrations and driving-related impairment following vaporization of low-THC/high-CBD cannabis (<1% THC) . Using pharmacokinetic data and blood samples from 27 participants, the present retrospective analysis investigated whether genotype-predicted CYP2C9 and CYP2C19 phenotypes influenced blood levels of THC and its metabolites after single and repeated vaporization. Genomic DNA was extracted from heparinized blood (QIAamp DNA Blood Mini Kit, QIAcube, QIAGEN) and quantified (Infinite Pro 200, TECAN) before allele-specific real-time PCR analysis (TaqMan Genotyping, QuantStudio 5, Thermo Fisher Scientific) to detect predefined function-impairing CYP2C9 and CYP2C19 variants. Genotypes were used to predict phenotypes based on validated allele definitions and functional annotations.

Approximately 44% of participants carried function-impairing CYP2C9 alleles and about 52% function-impairing CYP2C19 alleles, with the observed genotype-predicted phenotypes consistent with European population frequencies . Although no consistently statistically significant differences were observed in blood concentrations or metabolic ratios across predicted phenotypes, subtle trends emerged in CYP2C9 phenotypes among repeated consumers, suggesting that repeated cannabis use may induce metabolic activity more prominently in intermediate than in normal metabolizers. Specifically, CYP2C9-mediated hydroxylation to the first metabolite appeared faster, while the subsequent conversion to the second metabolite remained comparatively slower in intermediate metabolizers. CYP2C19 showed no evident effect.

The findings lay the groundwork for future pharmacogenetic research and establish an underexplored, but relevant area within forensic genetics, with implications for the ongoing global discourse on cannabis legalization. However, due to the retrospective design and limited sample size, the results are indicative but not generalizable, with potential confounders discussed. To confirm and expand upon these results, the “CANBiome” study is underway, incorporating larger study cohorts, controlling for external factors (e.g., CYP enzyme modulators), and combining forensic and clinical objectives.

Authors

• Janine Schulte (University of Basel, Department of Biomedical Engineering, Institute of Forensic Medicine, Switzerland)
• Leila Potzel (University of Basel, Department of Pharmaceutical Sciences, Biopharmacy, Switzerland)
• Priska Frei (University of Basel, Department of Biomedical Engineering, Institute of Forensic Medicine, Switzerland)
• Isabell Seibert (University of Basel, Department of Pharmaceutical Sciences, Biopharmacy, Switzerland)
• Kathrin Gerlach (University of Basel, Department of Biomedical Engineering, Institute of Forensic Medicine, Switzerland)
• Katja Mercer‑Chalmers‑Bender (University of Basel, Department of Biomedical Engineering, Institute of Forensic Medicine, Switzerland)
• Eva Scheurer (University of Basel, Department of Biomedical Engineering, Institute of Forensic Medicine, Switzerland)
• Henriette E. Meyer zu Schwabedissen (University of Basel, Department of Pharmaceutical Sciences, Biopharmacy, Switzerland)
• Iris Schulz (University of Basel, Department of Biomedical Engineering, Institute of Forensic Medicine, Switzerland)