{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,5]],"date-time":"2026-09-05T00:13:59Z","timestamp":1788567239034,"version":"build-2803163510"},"reference-count":23,"publisher":"MDPI AG","issue":"12","license":[{"start":{"date-parts":[[2023,11,23]],"date-time":"2023-11-23T00:00:00Z","timestamp":1700697600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Metabolites"],"abstract":"<jats:p>(\u2212)-trans-\u03949-tetrahydrocannabinol (\u03949-THC) is the primary psychoactive compound in the Cannabis sativa plant. \u03949-THC undergoes extensive metabolism, with the main human phase I metabolites being 11-hydroxy-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-tetrahydrocannabinol (THC-COOH). Early animal studies have indicated that the 9-10 double bond may be reduced in vivo to yield 11-hydroxy-hexahydrocannabinol (11-OH-HHC) and 11-nor-9-carboxy-hexahydrocannabinol (HHC-COOH). These metabolites have not been confirmed in humans. In this study, we aimed to investigate whether this metabolic transformation occurs in humans. A range of cannabinoids and metabolites, including 11-OH-HHC and HHC-COOH, were measured in whole blood from 308 authentic forensic traffic cases, of which 222 were positive for \u03949-THC. HHC-COOH and 11-OH-HHC were detected in 84% and 15% of the \u03949-THC positive cases, respectively, and the estimated median concentration of HHC-COOH was 7%, relative to that of THC-COOH. To corroborate the in vivo findings, \u03949-THC and its metabolites 11-OH-THC and THC-COOH were incubated with pooled human liver microsomes. HHC-COOH was detected in both the \u03949-THC and 11-OH-THC incubations, while 11-OH-HHC was only detectable in the 11-OH-THC incubation. Hexahydrocannabinol was not detected in any of the incubations, indicating that it is 11-OH-THC or the corresponding aldehyde that undergoes double bond reduction with subsequent oxidation of the aliphatic alcohol to HHC-COOH. In summary, the presented data provide the first evidence of HHC-COOH and 11-OH-HHC being human phase I metabolites of \u03949-THC. These findings have implications for interpretation of analytical results from subjects exposed to \u03949-THC or HHC.<\/jats:p>","DOI":"10.3390\/metabo13121169","type":"journal-article","created":{"date-parts":[[2023,11,23]],"date-time":"2023-11-23T03:45:18Z","timestamp":1700711118000},"page":"1169","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":16,"title":["Evidence of 11-Hydroxy-hexahydrocannabinol and 11-Nor-9-carboxy-hexahydrocannabinol as Novel Human Metabolites of \u03949-Tetrahydrocannabinol"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8887-070X","authenticated-orcid":false,"given":"Christian","family":"Falck J\u00f8rgensen","sequence":"first","affiliation":[{"name":"Section of Forensic Chemistry, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Frederik V\u2019s vej 11, DK-2100 Copenhagen, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8048-3222","authenticated-orcid":false,"given":"Brian","family":"Schou Rasmussen","sequence":"additional","affiliation":[{"name":"Section of Forensic Chemistry, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Frederik V\u2019s vej 11, DK-2100 Copenhagen, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-6974-5535","authenticated-orcid":false,"given":"Kristian","family":"Linnet","sequence":"additional","affiliation":[{"name":"Section of Forensic Chemistry, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Frederik V\u2019s vej 11, DK-2100 Copenhagen, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6502-3583","authenticated-orcid":false,"given":"Ragnar","family":"Thomsen","sequence":"additional","affiliation":[{"name":"Section of Forensic Chemistry, Department of Forensic Medicine, Faculty of Health and Medical Sciences, University of Copenhagen, Frederik V\u2019s vej 11, DK-2100 Copenhagen, Denmark"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2023,11,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1770","DOI":"10.1002\/cbdv.200790152","article-title":"Human Cannabinoid Pharmacokinetics","volume":"4","author":"Huestis","year":"2007","journal-title":"Chem. Biodivers."},{"key":"ref_2","first-page":"21","article-title":"Pharmacokinetics and Metabolism of \u03941-Tetrahydrocannabinol and Other Cannabinoids with Emphasis on Man","volume":"38","author":"Agurell","year":"1986","journal-title":"Pharmacol. Rev."},{"key":"ref_3","first-page":"241","article-title":"Human Hepatic Microsomal Metabolism of Delta 1-Tetrahydrocannabinol","volume":"20","author":"Bornheim","year":"1992","journal-title":"Drug Metab. Dispos."},{"key":"ref_4","first-page":"1135","article-title":"Further Urinary Metabolites of Delta 1-Tetrahydrocannabinol in Man","volume":"32","author":"Halldin","year":"1982","journal-title":"Arzneimittelforschung"},{"key":"ref_5","first-page":"764","article-title":"Urinary Metabolites of Delta 1-Tetrahydrocannabinol in Man","volume":"32","author":"Halldin","year":"1982","journal-title":"Arzneimittelforschung"},{"key":"ref_6","first-page":"297","article-title":"Identification of in Vitro Metabolites of Delta 1-Tetrahydrocannabinol Formed by Human Livers","volume":"10","author":"Halldin","year":"1982","journal-title":"Drug Metab. Dispos."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1415","DOI":"10.1016\/j.lfs.2006.12.032","article-title":"Cytochrome P450 Enzymes Involved in the Metabolism of Tetrahydrocannabinols and Cannabinol by Human Hepatic Microsomes","volume":"80","author":"Watanabe","year":"2007","journal-title":"Life Sci."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"445","DOI":"10.1111\/j.2042-7158.1980.tb12966.x","article-title":"Identification in Human Urine of Delta 9-Tetrahydrocannabinol-11-Oic Acid Glucuronide: A Tetrahydrocannabinol Metabolite","volume":"32","author":"Williams","year":"1980","journal-title":"J. Pharm. Pharmacol."},{"key":"ref_9","unstructured":"European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) (2023). Technical Report: Hexahydrocannabinol (HHC) and Related Substances, European Monitoring Centre for Drugs and Drug Addiction (EMCDDA)."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"533","DOI":"10.1016\/0091-3057(91)90359-A","article-title":"Comparative in Vitro Metabolism of the Cannabinoids","volume":"40","author":"Harvey","year":"1991","journal-title":"Pharmacol. Biochem. Behav."},{"key":"ref_11","doi-asserted-by":"crossref","unstructured":"Schirmer, W., Auw\u00e4rter, V., Kaudewitz, J., Sch\u00fcrch, S., and Weinmann, W. (2023). Identification of Human Hexahydrocannabinol Metabolites in Urine. Eur. J. Mass Spectrom., 14690667231200139.","DOI":"10.1177\/14690667231200139"},{"key":"ref_12","doi-asserted-by":"crossref","unstructured":"Manier, S.K., Angert Valdiviezo, J., Vollmer, A.C., Eckstein, N., and Meyer, M.R. (2023). Analytical Toxicology of the Semi-Synthetic Cannabinoid Hexahydrocannabinol Studied in Human Samples, Pooled Human Liver S9 Fraction, Rat Samples and Drug Products Using HPLC-HRMS-MS. J. Anal. Toxicol., bkad079.","DOI":"10.1093\/jat\/bkad079"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"495","DOI":"10.1111\/j.2042-7158.1977.tb11376.x","article-title":"Identification of Metabolites of Delta1- and Delta1(6)-Tetrahydrocannabinol Containing a Reduced Double Bond","volume":"29","author":"Harvey","year":"1977","journal-title":"J. Pharm. Pharmacol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"389","DOI":"10.1002\/bms.1200150706","article-title":"In Vivo Metabolism of the Methyl Homologues of Delta-8-Tetrahydrocannabinol, Delta-9-Tetrahydrocannabinol and Abn-Delta-8-Tetrahydrocannabinol in the Mouse","volume":"15","author":"Brown","year":"1988","journal-title":"Biomed. Env. Mass Spectrom."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"324","DOI":"10.1002\/bms.1200200514","article-title":"In Vivo Metabolism of the Ethyl Homologues of Delta-8-Tetrahydrocannabinol and Delta-9-Tetrahydrocannabinol in the Mouse","volume":"20","author":"Brown","year":"1991","journal-title":"Biol. Mass Spectrom."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"280","DOI":"10.1093\/jat\/bks014","article-title":"Validation of a Fully Automated Robotic Setup for Preparation of Whole Blood Samples for LC-MS Toxicology Analysis","volume":"36","author":"Andersen","year":"2012","journal-title":"J. Anal. Toxicol."},{"key":"ref_17","first-page":"1","article-title":"The pandas development team Pandas-Dev\/Pandas: Pandas","volume":"21","author":"Team","year":"2022","journal-title":"Zenodo"},{"key":"ref_18","unstructured":"Plotly Technologies Inc. (2023, November 22). Collaborative Data Science. Available online: https:\/\/plot.ly."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"357","DOI":"10.1038\/s41586-020-2649-2","article-title":"Array Programming with NumPy","volume":"585","author":"Harris","year":"2020","journal-title":"Nature"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"261","DOI":"10.1038\/s41592-019-0686-2","article-title":"SciPy 1.0: Fundamental Algorithms for Scientific Computing in Python","volume":"17","author":"Virtanen","year":"2020","journal-title":"Nat. Methods"},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"362","DOI":"10.3109\/03602532.2014.910219","article-title":"Carbon-Carbon Double-Bond Reductases in Nature","volume":"46","author":"Huang","year":"2014","journal-title":"Drug Metab. Rev."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"236","DOI":"10.1016\/j.cbi.2014.09.024","article-title":"The Aldo-Keto Reductases (AKRs): Overview","volume":"234","author":"Penning","year":"2015","journal-title":"Chem. Biol. Interact."},{"key":"ref_23","first-page":"223","article-title":"7-Oxo-Delta1-Tetrahydrocannabinol: A Novel Metabolite of Delta1-Tetrahydrocannabinol","volume":"8","author":"Burstein","year":"1974","journal-title":"Res. Commun. Chem. Pathol. Pharmacol."}],"container-title":["Metabolites"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2218-1989\/13\/12\/1169\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T21:27:52Z","timestamp":1760131672000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2218-1989\/13\/12\/1169"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,11,23]]},"references-count":23,"journal-issue":{"issue":"12","published-online":{"date-parts":[[2023,12]]}},"alternative-id":["metabo13121169"],"URL":"https:\/\/doi.org\/10.3390\/metabo13121169","relation":{},"ISSN":["2218-1989"],"issn-type":[{"value":"2218-1989","type":"electronic"}],"subject":[],"published":{"date-parts":[[2023,11,23]]}}}