In vitro metabolism of Δ8-, Δ9-, and Δ10-THC in human hepatocytes. Distinct Δ10-THC biotransformation and implications for drug testing

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.