Detection of 11-nor-9-carboxy-hexahydrocannabinol (HHC-COOH) as metabolite of both hexahydrocannabinol (HHC) and Δ9-tetrahydrocannabinol (Δ9-THC) in routine forensic samples

Hexahydrocannabinol (HHC) is a phytocannabinoid that has been known since 1940, but has only recently appeared on the recreational drug market. For the analytical detection of HHC consumption, a GC-MS method for the quantification of cannabinoids was extended and validated by adding (9S)-HHC, (9 R)-HHC, (9S)-carboxy-HHC (HHC-COOH) and (9 R)-HHC-COOH. Both HHC and HHC-COOH epimers were chromatographically separated and the validation data were convincing for forensic toxicological routine analysis. This method was used to analyze 599 serum samples from forensic cases where cannabis use was suspected. Results were classified into three consumption groups: Δ⁹-THC only (n = 574), Δ⁹-THC and HHC (n = 19), and HHC only (n = 6). The concentration in serum was between 0.15 ng/mL to 14.4 ng/mL for (9 R)-HHC and 0.14 ng/mL to 5.76 ng/mL for (9S)-HHC. In all HHC positive samples, (9 R)-HHC-COOH could be detected in concentrations between 1.0 and 314 ng/mL. Of note, in the cases that tested positive for Δ⁹-THC only, (9 R)-HHC-COOH was also unambiguously detected in serum samples as a metabolite not only of HHC but also of Δ⁹-THC. In six urine samples of THC users that were examined by GC-MS and LC-MS/MS both epimers of HHC-COOH and their glucuronides could be detected. (9S)-HHC-COOH was the predominant epimer in urine which was not detected in serum. Results suggest that detection of HHC-COOH epimers alone cannot prove prior HHC consumption. With the data presented, we tentatively recommend a cut-off of 30 % of the (9 R)-HHC-COOH/THC-COOH ratio in serum to distinguish the intake of both substances from the intake of Δ⁹-THC alone.