Postmortem testing reveals the limits of THC evidence

The growing popularity of delta-8-tetrahydrocannabinol (Δ8-THC) products has introduced new analytical and interpretive challenges for forensic toxicology laboratories. While delta-9-tetrahydrocannabinol (Δ9-THC) and its metabolites have been extensively characterized in postmortem casework, comparable data for Δ8-THC remain scarce. This study presents a validated LC-MS/MS method for the quantitation of Δ8-THC, Δ9-THC, and their primary metabolites in postmortem blood. Sample preparation employed liquid-liquid extraction using water acidified with 10% acetic acid, followed by extraction with hexane: ethyl acetate (90:10, v/v). The validated method was subsequently applied to a selected subset of authentic postmortem blood samples (n = 107) previously identified to contain Δ8- and/or Δ9-THC-COOH by GC-MS urine testing. Among these cannabinoid-positive urine cases, 39.3% were positive in blood for both Δ8- and Δ9-THC and their metabolites, whereas 25.2% and 14.0% were positive for only Δ8-THC and Δ9-THC-related analytes, respectively. Δ8-THC blood concentrations ranged from 1.0 to 90.4 ng/mL, and Δ8-THC-COOH concentrations ranged from 5.1 to 1484 ng/mL. Additionally, 11-OH-Δ8-THC was measured in 11.2% of cases and consistently co-occurred with Δ8-THC and Δ8-THC-COOH. These findings provide descriptive postmortem concentration data for Δ8-THC and highlight the importance of adequate chromatographic resolution of THC isomers. Importantly, we also underscore the interpretive challenges of polycannabinoid findings in postmortem casework, where detection of Δ8-THC, Δ9-THC, and/or their metabolites should be interpreted as evidence of cannabinoid exposure, and not as definitive evidence of impairment, intoxication, or contribution to death without additional case context.