In Vitro Metabolism of Δ 8 ‐, Δ 9 ‐, and Δ 10 ‐THC in Human Hepatocytes: Distinct Δ 10 ‐THC Biotransformation and Implications for Drug Testing

ABSTRACT With its widespread recreational and increasing medical use, ∆ 9 ‐tetrahydrocannabinol (∆ 9 ‐THC), the main psychoactive compound in cannabis, is regularly subjected to drug testing in clinical and forensic toxicology. ∆ 8 ‐ and ∆ 10 ‐THC have recently entered unregulated drug markets. Their close structural similarity to ∆ 9 ‐THC poses various analytical challenges, with a high risk of misidentification and misinterpretation of bioanalytical data. This study investigated the in vitro metabolic fate of ∆ 8 ‐ and ∆ 10 ‐THC in comparison to ∆ 9 ‐THC using human hepatocytes and high‐performance liquid chromatography coupled to high‐resolution time‐of‐flight analysis (HPLC‐QToF). A comparable metabolism was observed for ∆ 8 ‐THC and ∆ 9 ‐THC, with the formation of the monohydroxy and carboxy metabolites and their glucuronides. In contrast, ∆ 10 ‐THC was found to be extensively glucuronidated (forming ∆ 10 ‐THC‐glucuronide) and monohydroxylated, with only minor formation of a carboxy metabolite. Structural considerations led to the hypothesis that ∆ 10 ‐THC is predominantly hydroxylated at a different site than ∆ 8 ‐THC and ∆ 9 ‐THC. THC isomers should be considered in cannabis drug testing. The differing metabolism of ∆ 10 ‐THC exacerbates the risk of misinterpretation of analytical results.