Hexahydrocannabinol and closely related semi-synthetic cannabinoids: A comprehensive review

In vitro activation of the CB1 receptor by the semi-synthetic cannabinoids hexahydrocannabinol (HHC), hexahydrocannabinol acetate (HHC-O) and hexahydrocannabiphorol (HHC-P)

Semi-synthetic cannabinoids (SSCs) including hexahydrocannabinol (HHC) are emerging on the drug market and sold openly as purportedly legal replacements for cannabis and Δ9-THC. By the beginning of 2024, 24 European countries had identified HHC, often sold openly in edibles (foods/candy), vapes and low-THC cannabis flowers and resins. The SSC market is developing rapidly, with HHC acetate (HHC-O), hexahydrocannabiphorol (HHC-P) and others recently identified. These developments may mark the first major change in the market for 'legal' replacements to cannabis since 'Spice' containing synthetic cannabinoids, such as JWH-018, emerged in 2008. Currently, there are some data available on the pharmacology of SSCs, which is crucial for understanding their effects, evaluating health risks and informing public health responses. This study focused on characterizing the in vitro activation of the human CB1 receptor by the (R)- and (S)-epimers of HHC, HHC-P and HHC-O. Using recombinant CHO-K1 cells expressing the human CB1 receptor, the potency (EC50) and efficacy were determined. It was established that (9R)-HHC and (9R)-HHC-P activated the CB1 receptor as partial agonists and with five and two times lower potency compared to JWH-018, respectively, while the (S)-epimers exhibited even lower potency. The (R)-epimer of HHC-O activate the CB1 receptor to even lesser extent and the (S)-epimer showed no activation. For HHC and HHC-P, all epimers exhibited similar level of efficacy. This available evidence suggests cannabimimetic effects of the tested SSC with the exception for the acetates that likely function as pro-drugs in vivo.

Human metabolism of the semi-synthetic cannabinoids hexahydrocannabinol, hexahydrocannabiphorol and their acetates using hepatocytes and urine samples

Hexahydrocannabinol (HHC), hexahydrocannabiphorol (HHCP) and their acetates, HHC-O and HHCP-O, respectively, are emerging in Europe as alternatives to tetrahydrocannabinol (THC). This study aimed to elucidate the metabolic pathways of the semi-synthetic cannabinoids HHC, HHCP, HHC-O and HHCP-O from incubation with human hepatocytes. The metabolites of HHC were also identified in authentic urine samples. HHC, HHCP, HHC-O and HHCP-O were incubated with primary human hepatocytes for 1, 3 and 5 h. Authentic urine samples from cases screened positive for cannabis in blood using ELISA but confirmed negative were analysed both non-hydrolysed and hydrolysed for HHC metabolites. Potential metabolites were identified using ultra-high performance liquid chromatography (UHPLC) coupled to a quadrupole time-of-flight mass spectrometer (QToF-MS). HHC and HHCP were primarily metabolised through monohydroxylation (monoOH), followed by oxidation to a carboxylic acid metabolite. HHC-O and HHCP-O were rapidly metabolised to HHC and HHCP, respectively. In authentic urine samples, 18 different metabolites were identified, and 99.3% of hydroxylated metabolites were glucuronidated. 11-OH-HHC, 5'OH-HHC and another metabolite with a monoOH on the side chain were the only metabolites present in all 16 urine samples. The metabolism of HHC and HHCP were similar, although the longer alkyl side chain of HHCP (heptyl) led to greater hydroxylation on the side chain than HHC (pentyl). The use of HHC and HHCP can be differentiated from the use of THC and other phytocannabinoids, but the use of the acetate analogues may not be differentiable from their non-acetate analogues.

Quantitation of hexahydrocannabinol (HHC) and metabolites in blood from DUID cases

Hexahydrocannabinol (HHC) was first reported in the EU in May 2022. HHC has three chiral carbon atoms, but only (6aR,9R,10aR)-HHC (9R-HHC) and (6aR,9S,10aR)-HHC (9S-HHC) have been encountered in HHC products. The aim of this study was to develop and validate a method for the quantitative analysis of 9R-HHC, 9S-HHC, 11-OH-9R-HHC, 9R-HHC-COOH, 9S-HHC-COOH and 8-OH-9R-HHC. In addition, an objective was to investigate the immunochemical cross-reactivity. Blood samples from driving under the influence of drugs (DUID) cases screened positive for cannabis using enzyme-linked immunoadsorbent assay (ELISA) and confirmed negative for tetrahydrocannabinol (THC), 11-hydroxy-THC and THC-COOH were reanalyzed with a newly validated HHC method to investigate the presence of HHC and metabolites. The LC-MS-MS method was validated for matrix effects, lower limit of quantification (LLOQ), calibration model, precision, bias and autosampler stability. Cross-reactivity on an ELISA method was investigated separately for 9R-HHC-COOH and 9S-HHC-COOH at a concentration range between 5 and 200 ng/mL. The cross-reactivity was found to be 120% for 9R-HHC-COOH and 48% for 9S-HHC-COOH. In the LC-MS-MS method, 9R-HHC-COOH, 9S-HHC-COOH and 11-OH-9R-HHC showed matrix effects <25% at both concentrations, while 8-OH-9R-HHC, 9R-HHC and 9S-HHC matrix effects exceeded 25% at both concentrations but showed good precision (<10% for both inter and intra day) and low bias (<6%) in the further validation. The LLOQ was investigated and established at 0.2 ng/mL for all analytes except the carboxylated metabolites that had an LLOQ of 2.0 ng/mL. The upper LOQ was 20 and 200 ng/mL, respectively. Reanalysis of cases (n = 145) confirmed HHC and metabolites in 32 cases (22%). It was determined that the major metabolite in blood after administration of HHC was 9R-HHC-COOH followed by 11-OH-9R-HHC and that presumptive positive cases are caught by the routine ELISA screening for cannabis.

Investigation of the intrinsic cannabinoid activity of hemp-derived and semisynthetic cannabinoids with β-arrestin2 recruitment assays-and how this matters for the harm potential of seized drugs

Cultivation of industrial low-Δ9-tetrahydrocannabinol (Δ9-THC) hemp has created an oversupply of cannabidiol (CBD)-rich products. The fact that phytocannabinoids, including CBD, can be used as precursors to synthetically produce a range of THC variants-potentially located in a legal loophole-has led to a diversification of cannabis recreational drug markets. 'Hemp-compliant', 'hemp-derived' and 'semisynthetic' cannabinoid products are emerging and being advertised as (legal) alternatives for Δ9-THC. This study included a large panel (n = 30) of THC isomers, homologs, and analogs that might be derived via semisynthetic procedures. As a proxy for the abuse potential of these compounds, we assessed their potential to activate the CB1 cannabinoid receptor with a β-arrestin2 recruitment bioassay (picomolar-micromolar concentrations). Multiple THC homologs (tetrahydrocannabihexol, THCH; tetrahydrocannabiphorol, THCP; tetrahydrocannabinol-C8, THC-C8) and THC analogs (hexahydrocannabinol, HHC; hexahydrocannabiphorol, HHCP) were identified that showed higher potential for CB1 activation than Δ9-THC, based on either higher efficacy (Emax) or higher potency (EC50). Structure-activity relationships were assessed for Δ9-THC and Δ8-THC homologs encompassing elongated alkyl chains. Additionally, stereoisomer-specific differences in CB1 activity were established for various THC isomers (Δ7-THC, Δ10-THC) and analogs (HHC, HHCP). Evaluation of the relative abundance of 9(S)-HHC and 9(R)-HHC epimers in seized drug material revealed varying epimeric compositions between batches. Increased abundance of the less active 9(S)-HHC epimer empirically resulted in decreased potency, but sustained efficacy for the resulting diastereomeric mixture. In conclusion, monitoring of semisynthetic cannabinoids is encouraged as the dosing and the relative composition of stereoisomers can impact the harm potential of these drugs, relative to Δ9-THC products.

An emerging trend in Novel Psychoactive Substances (NPSs): designer THC

Since its discovery as one of the main components of cannabis and its affinity towards the cannabinoid receptor CB1, serving as a means to exert its psychoactivity, Δ9-tetrahydrocannabinol (Δ9-THC) has inspired medicinal chemists throughout history to create more potent derivatives. Initially, the goal was to synthesize chemical probes for investigating the molecular mechanisms behind the pharmacology of Δ9-THC and finding potential medical applications. The unintended consequence of this noble intent has been the proliferation of these compounds for recreational use. This review comprehensively covers the most exhaustive number of THC-like cannabinoids circulating on the recreational market. It provides information on the chemistry, synthesis, pharmacology, analytical assessment, and experiences related to the psychoactive effects reported by recreational users on online forums. Some of these compounds can be found in natural cannabis, albeit in trace amounts, while others are entirely artificial. Moreover, to circumvent legal issues, many manufacturers resort to semi-synthetic processes starting from legal products extracted from hemp, such as cannabidiol (CBD). Despite the aim to encompass all known THC-like molecules, new species emerge on the drug users' pipeline each month. Beyond posing a significantly high public health risk due to unpredictable and unknown side effects, scientific research consistently lags behind the rapidly evolving recreational market.

Cross-Reactivity of 24 Cannabinoids and Metabolites in blood using the immunalysis cannabinoids direct enzyme-linked immunosorbent assay kit

With a wider availability of synthetic and semi-synthetic cannabinoids in the consumer space, there is a growing impact on public health and safety. Forensic toxicology laboratories should keep these compounds in mind as they attempt to remain effective in screening for potential sources of human performance impairment. Enzyme-linked immunosorbent assay (ELISA) is a commonly utilized tool in forensic toxicology, as its efficiency and sensitivity make it useful for rapid and easy screening for a large number of drugs. This screening technique has lower specificity, which allows for broad cross-reactivity among structurally-similar compounds. In this study, the Cannabinoids Direct ELISA kit from Immunalysis was utilized to assess the cross-reactivities of 24 cannabinoids and metabolites in whole blood. The assay was calibrated with 5 ng/mL of 11-nor-9-carboxy-Δ9-tetrahydrocannabinol and the analytes of interest were evaluated at concentrations ranging from 5 to 500 ng/mL. Most parent compounds demonstrated cross-reactivity ≥ 20 ng/mL, with increasing alkyl side chain length relative to Δ9-tetrahydrocannabinol resulting in decreased cross-reactivity. Of the 24 analytes, only the carboxylic acid metabolites, 11-nor-9-carboxy-Δ8-tetrahydrocannabinol, 11-nor-9(R)-carboxy-hexahydrocannabinol, and 11-nor-9(S)-carboxy-hexahydrocannabinol, were cross-reactive at levels ≤ 10 ng/mL. Interestingly, 11-nor-9(R)-carboxy-hexahydrocannabinol demonstrated cross-reactivity at 5 ng/mL, where its stereoisomer 11-nor-9(S)-carboxy-hexahydrocannabinol, did not. As more information emerges about the prevalence of these analytes in blood specimens, it is important to understand and characterize their impact on current testing paradigms.

Identification and quantification of both isomers of hexahydrocannabinol, (9R)-hexahydrocannabinol and (9S)-hexahydrocannabinol, in three different matrices by mass spectrometry

CONTEXT

Hexahydrocannabinol (HHC), a compound derived from synthetic production using cannabidiol (CBD) or delta-9-tetrahydrocannabinol (Δ9 -THC), has gained recent attention due to its presence in seized materials across Europe. Sold legally in various forms, HHC poses potential health risks, particularly as a legal alternative to THC in some countries. Despite its historical description in the 1940s, limited toxicology data, pharmacological understanding, and analytical methods for HHC exist.

METHOD

This study proposes analytical techniques using mass spectrometry to detect, identify, and quantify (9R)-HHC and (9S)-HHC, concurrently with THC and CBD in various matrices, including oral fluid, whole blood, and seized material. Three distinct methods were employed for different matrices: GC/MS for seized material, GC/MS/MS for whole blood, and UHPLC/MS/MS for oral fluid. Methods were validated qualitatively for oral fluid with a FLOQSwab® device and quantitatively in whole blood and seized material according to Peters et al's recommendations and ICH guidelines.

RESULTS

Validated methods were considered reliable in detecting and quantifying HHC isomers in terms of repeatability, reproducibility, and linearity with r2 systematically >0.992. These methods were applied to authentic cases, including seized materials and biological samples from traffic control (whole blood and oral fluid). In seized materials, (9R)-HHC levels ranged from 2.09% to 8.85% and (9R)-HHC/(9S)-HHC ratios varied from 1.36 to 2.68. In whole blood sample, (9R)-HHC and (9S)-HHC concentrations were, respectively, 2.38 and 1.39 ng/mL. For all analyzed samples, cannabinoids such as THC and CBD were also detected.

CONCLUSION

This research contributes analytical insights into differentiating and simultaneously analyzing (9R)-HHC and (9S)-HHC, using widely applicable mass spectrometric methods. The study emphasizes the need for vigilance among toxicologists, as new semisynthetic cannabinoids continue to emerge in Europe, with potential health implications. The findings underscore the importance of reliable analytical methods for monitoring these compounds in forensic and clinical settings.

Appearance of hexahydrocannabinols as recreational drugs and implications for cannabis drug testing - focus on HHC, HHC-P, HHC-O and HHC-H

This study investigated the effects of hexahydrocannabinol (HHC) and other unclassified cannabinoids, which were recently introduced to the recreational drug market, on cannabis drug testing in urine and oral fluid samples. After the appearance of HHC in Sweden in 2022, the number of posts about HHC on an online drug discussion forum increased significantly in the spring of 2023, indicating increased interest and use. In parallel, the frequency of false positive screening tests for tetrahydrocannabinol (THC) in oral fluid, and for its carboxy metabolite (THC-COOH) in urine, rose from <2% to >10%. This suggested that HHC cross-reacted with the antibodies in the immunoassay screening, which was confirmed in spiking experiments with HHC, HHC-COOH, HHC acetate (HHC-O), hexahydrocannabihexol (HHC-H), hexahydrocannabiphorol (HHC-P), and THC-P. When HHC and HHC-P were classified as narcotics in Sweden on 11 July 2023, they disappeared from the online and street shops market and were replaced by other unregulated variants (e.g. HHC-O and THC-P). In urine samples submitted for routine cannabis drug testing, HHC-COOH concentrations up to 205 (mean 60, median 27) µg/L were observed. To conclude, cannabis drug testing cannot rely on results from immunoassay screening, as it cannot distinguish between different tetra- and hexahydrocannabinols, some being classified but others unregulated. The current trend for increased use of unregulated cannabinols will likely increase the proportion of positive cannabis screening results that need to be confirmed with mass spectrometric methods. However, the observed cross-reactivity also means a way to pick up use of new cannabinoids that otherwise risk going undetected.

LC-MS/MS analysis of 11-nor-9-carboxy-hexahydrocannabinol (HHC-COOH) and 11-hydroxy-hexahydrocannabinol (HHC-OH) for verification of hexahydrocannabinol (HHC) intake

Natural and semi-synthetic cannabinoid analogs are getting increasing media attention for their recreative use as an alternative to traditional cannabis, in Sweden as well as internationally. To investigate an increasing number of urine samples incoming to our clinical laboratory that were screening positive, using a CEDIA THC-COOH immunoassay from ThermoFisher Scientific, but then testing negative using GC-MS based verification analysis, we developed an LC-MS/MS-method for verification of hexahydrocannabinol (HHC) and Δ8-tetrahydrocannabinol. Assessment of HHC intake was based on identification of the following four metabolites: 11-nor-9(R)-carboxy-hexahydrocannabinol (R-HHC-COOH), 11-nor-9(S)-carboxy-hexahydrocannabinol (S-HHC-COOH), 11-hydroxy-9(R)-hexahydrocannabinol (R-HHC-OH) and 11-hydroxy-9(S)-hexahydrocannabinol (S-HHC-OH). Out of 46 urine samples analysed in this study, 44 showed presence of HHC-metabolites, which indicate HHC as the main explanation for an increased number of negative verifications for THC-COOH. In these samples, the HHC-OH metabolites occurred at a higher concentration than R-HHC-COOH while S-HHC-COOH was only detected in few samples at low concentrations. R-HHC-COOH and S-HHC-COOH can easily be added to a pre-existing verification method for THC-COOH, and still show acceptable results, while HHC-OH requires an enzyme capable of hydrolysing the ether glucuronide bond.

Disposition of Hexahydrocannabinol Epimers and Their Metabolites in Biological Matrices following a Single Administration of Smoked Hexahydrocannabinol: A Preliminary Study

In 2023, hexahydrocannabinol (HHC) attracted the attention of international agencies due to its rapid spread in the illegal market. Although it was discovered in 1940, less is known about the pharmacology of its two naturally occurring epimers, 9(R)-HHC and 9(S)-HHC. Thus, we aimed to investigate the disposition of hexahydrocannabinol epimers and their metabolites in whole blood, urine and oral fluid following a single controlled administration of a 50:50 mixture of 9(R)-HHC and 9(S)-HHC smoked with tobacco. To this end, six non-user volunteers smoked 25 mg of the HHC mixture in 500 mg of tobacco. Blood and oral fluid were sampled at different time points up to 3 h after the intake, while urine was collected between 0 and 2 h and between 2 and 6 h. The samples were analyzed with a validated HPLC-MS/MS method to quantify 9(R)-HHC, 9(S)-HHC and eight metabolites. 9(R)-HHC showed the highest Cmax and AUC0-3h in all the investigated matrices, with an average concentration 3-fold higher than that of 9(S)-HHC. In oral fluid, no metabolites were detected, while they were observed as glucuronides in urine and blood, but with different profiles. Indeed, 11nor-9(R)-HHC was the most abundant metabolite in blood, while 8(R)OH-9(R) HHC was the most prevalent in urine. Interestingly, 11nor 9(S) COOH HHC was detected only in blood, whereas 8(S)OH-9(S) HHC was detected only in urine.

Cannabidiol-Derived Cannabinoids: The Unregulated Designer Drug Market Following the 2018 Farm Bill

Background

In this review, we summarize current scientific knowledge on psychoactive cannabinoids synthesized from cannabidiol (CBD) and sold in the semi-legal market established in response to the passage of the US Agriculture Improvement Act of 2018, commonly known as the 2018 Farm Bill. The discussion focuses on recent developments that suggest this unregulated market may be fertile ground for a potential health crisis.

Summary

Current research into CBD-derived cannabinoids is mainly limited to Δ8-tetrahydrocannabinol (Δ8-THC) products, with some recent publications beginning to explore O-acetyl-THC, a term describing the acetate ester of Δ8-THC or Δ9-THC, and its potential pulmonary toxicity. We advance the discussion on the CBD-derived cannabinoid market, shedding light on the introduction and associated dangers of novel cannabinoids, likely produced via fully synthetic routes using sidechain variants of CBD, with purportedly greater agonist activity at the human cannabinoid receptor 1 (as a source of euphorigenic activity) than Δ9-THC. We discuss the expanded incorporation of the acetate ester motif into other THC analogues. We also discuss the lack of regulatory oversight for the production of CBD-derived cannabinoids and the unlabeled presence of under-researched cannabinoids formed as reaction side products in the CBD-derived cannabinoid products being sold. Accordingly, we suggest approaches to monitoring the CBD-derived cannabinoid market and investigating the pharmacology of the cannabinoids being consumed. Finally, important epidemiological findings are discussed and future directions for research are suggested to call investigators to this critically understudied field.

Key Messages

The CBD-derived cannabinoid market is growing internationally, and the market has diversified to include potent synthetic cannabinoids. The products sold on this unregulated market are under-researched despite growing availability and consumer interest. Ernest investigation of the pharmacology of these novel cannabinoids and the contents of CBD-derived cannabinoid products is critical for monitoring this potential source of another vaping-related epidemic.

Molecular Insights of New Psychoactive Substances (NPS) 2.0

The New Psychoactive Substances (NPS) phenomenon represents an ever-changing global issue, with a number of new molecules entering the illicit market every year in response to international banning laws [...].

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

Hexahydrocannabinol (HHC) is an emerging semi-synthetic cannabinoid, which is obtained from cyclization of cannabidiol and subsequent hydrogenation. As a potentially legal alternative of ∆9-tetrahydrocannabinol (∆9-THC), it is increasingly seized in the USA and Europe. The aims of this study were to investigate the metabolism of HHC in pooled human liver S9 fraction (pHLS9), rat and human samples. Additionally, a locally obtained low-THC cannabis product was investigated, which was advertised with an elevated concentration of HHC. Overall, HHC formed an 11-hydroxy (HO) metabolite, as well as a carboxy metabolite. While only the parent compound was detected in rat urine and feces, the hydroxy metabolite was additionally detected in pHLS9 and human plasma. The carboxy metabolite was only detectable in human plasma. The metabolism corresponded well to that of ∆9-THC, although glucuronidation and the formation of an 8-HO metabolite were not observed. Detectability of HHC and its carboxy metabolite in rat urine was investigated using gas chromatography-mass spectrometry, but neither the parent compound nor the metabolite were detectable. The investigated low-THC cannabis product appeared to be an actual cannabis product since, in addition to HHC, cannabinol, cannabidiol and ∆9-THC were detected after qualitative analysis. Estimation of its content revealed not only 30.6% of HHC but also 4% of ∆9-THC.

A Survey Study of Individuals Using Hexahydrocannabinol Cannabis Products: Use Patterns and Perceived Effects

Introduction: Across the cannabis market, multiple cannabinoids have seen rapid growth. Considering the differing effects between specific cannabinoids, it is critical to assess effects on an individual level. Hexahydrocannabinol (HHC) is one intoxicating cannabinoid that became more accessible due to regulatory shifts. The purpose of the current study was to provide descriptive data regarding HHC use patterns and perceived effects within a sample of participants who endorsed recent HHC use. Methods: One hundred nine individuals self-reported use of an HHC-cannabis product at least once within 6 months and completed an HHC use questionnaire via Prolific, an online crowdsourcing platform. Results: Findings suggest recent HHC users are using HHC relatively frequently (∼10 days during the past month) for various indications, including anxiety and pain. HHC was perceived to yield more good than bad effects, including relaxation and euphoria. Approximately 17% of the sample reported adverse effects, and ∼20% of those who stopped using HHC experienced some withdrawal symptoms. Few meaningful sex differences in subjective effect ratings were observed. Discussion: The current study provides critical preliminary data about consumer use patterns and perceived effects related to HHC. Such data are needed to further research on the potential therapeutic as well as detrimental effects of HHC and to better inform the consumers, health professionals, and regulators about a cannabinoid that is widely available the market.

Identification of human hexahydrocannabinol metabolites in urine

Hexahydrocannabinol (HHC) is a cannabinoid that has been known since 1940 but has only recently found its way into recreational use as a psychoactive drug. HHC has been used as a legal alternative to tetrahydrocannabinol (THC) in many countries, but first countries already placed it under their narcotic substances law. Our aim was to evaluate a reliable analytical method for the proof of HHC consumption by LC-MS/MS and GC-MS. We identified the two epimers of HHC and metabolites after HHC consumption by two volunteers (inhalation by use of a vaporizer and oral intake). LC-HR-MS/MS, LC-MS/MS and GC-MS with literature data (EI-MS spectra of derivatives) and reference compounds - as far as commercially available - were used for metabolite identification. Phase-II-metabolites (glucuronides) of HHC and OH-HHC were found in urine samples with LC-HR-MS/MS and LC-MS/MS. The main metabolite was tentatively identified with GC-MS as 4'OH-HHC (stereochemistry on C9 and C4' unknown). Another major side-chain hydroxylated metabolite found by LC-MS/MS could not be unambiguously identified. Both epimers of 11-OH-HHC were found in considerable amounts in urine. (8R, 9R)-8-OH-HHC was identified as a minor metabolite with GC-MS and LC-MS/MS. While (9S)-HHC was found in urine after oral intake and inhalation of HHC, the more psychoactive epimer (9R)-HHC was only found in urine after inhalation. Several other minor metabolites were detected but not structurally identified. We found that after oral or inhalative consumption the urinary main metabolites of a diastereomeric mixture of HHC are different from the respective, major Δ9-THC metabolites (11-OH-Δ9-THC and 11-nor-9-carboxy-Δ9-THC). Although a sensitive LC-MS/MS and GC-SIM-MS method were set-up for the reference compounds (9R)-11-nor-9-carboxy-HHC and (9S)-11-nor-9-carboxy-HHC, these oxidation products were not detected in urine with these techniques. To further increase sensitivity, a GC-MS/MS method was developed, and the 11-nor-9-carboxy metabolites of HHC were confirmed to be present as minor metabolites.

Studies Pertaining to the Emerging Cannabinoid Hexahydrocannabinol (HHC)

We report studies pertaining to two isomeric hexahydrocannabinols (HHCs), (9R)-HHC and (9S)-HHC, which are derivatives of the psychoactive cannabinoids Δ9- and Δ8-THC. HHCs have been known since the 1940s, but have become increasingly available to the public in the United States and are typically sold as a mixture of isomers. We show that (9R)-HHC and (9S)-HHC can be prepared using hydrogen-atom transfer reduction, with (9R)-HHC being accessed as the major diastereomer. In addition, we report the results of cannabinoid receptor studies for (9R)-HHC and (9S)-HHC. The binding affinity and activity of isomer (9R)-HHC are similar to that of Δ9-THC, whereas (9S)-HHC binds strongly in cannabinoid receptor studies but displays diminished activity in functional assays. This is notable, as our examination of the certificates of analysis for >60 commercially available HHC products show wide variability in HHC isomer ratios (from 0.2:1 to 2.4:1 of (9R)-HHC to (9S)-HHC). These studies suggest the need for greater research and systematic testing of new cannabinoids. Such efforts would help inform cannabis-based policies, ensure the safety of cannabinoids, and potentially lead to the discovery of new medicines.

Saturated Cannabinoids: Update on Synthesis Strategies and Biological Studies of These Emerging Cannabinoid Analogs

Natural and non-natural hexahydrocannabinols (HHC) were first described in 1940 by Adam and in late 2021 arose on the drug market in the United States and in some European countries. A background on the discovery, synthesis, and pharmacology studies of hydrogenated and saturated cannabinoids is described. This is harmonized with a summary and comparison of the cannabinoid receptor affinities of various classical, hybrid, and non-classical saturated cannabinoids. A discussion of structure-activity relationships with the four different pharmacophores found in the cannabinoid scaffold is added to this review. According to laboratory studies in vitro, and in several animal species in vivo, HHC is reported to have broadly similar effects to Δ9-tetrahydrocannabinol (Δ9-THC), the main psychoactive substance in cannabis, as demonstrated both in vitro and in several animal species in vivo. However, the effects of HHC treatment have not been studied in humans, and thus a biological profile has not been established.

Synthesis and pharmacological activity of the epimers of hexahydrocannabinol (HHC)

Cannabis is a multifaceted plant with numerous therapeutic properties on one hand, and controversial psychotropic activities on the other hand, which are modulated by CB1 endocannabinoid receptors. Δ9-Tetrahydrocannabinol (Δ9-THC) has been identified as the main component responsible for the psychotropic effects, while its constitutional isomer cannabidiol (CBD) has shown completely different pharmacological properties. Due to its reported beneficial effects, Cannabis has gained global popularity and is openly sold in shops and online. To circumvent legal restrictions, semi-synthetic derivatives of CBD are now frequently added to cannabis products, producing "high" effects similar to those induced by Δ9-THC. The first semi-synthetic cannabinoid to appear in the EU was obtained through cyclization and hydrogenation of CBD, and is known as hexahydrocannabinol (HHC). Currently, there is limited knowledge regarding HHC, its pharmacological properties, and its prevalence, as it is not commonly investigated in routine toxicological assays. In this study, synthetic strategies were explored to obtain an excess of the active epimer of HHC. Furthermore, the two epimers were purified and individually tested for their cannabinomimetic activity. Lastly, a simple and rapid chromatographic method employing a UV detector and a high-resolution mass spectrometer was applied to identify and quantify up to ten major phytocannabinoids, as well as the HHC epimers, in commercial cannabis samples.

Hexahydrocannabinol Pharmacology, Toxicology, and Analysis: The First Evidence for a Recent New Psychoactive Substance

BACKGROUND

During the last two years, hexahydrocannabinol (HHC), the hydrogenated derivative of tetrahydrocannabinol has been freely sold by internet websites as a "legal" replacement to THC and cannabis in a range of highly attractive branded and unbranded products, some of which are sold as "legal highs". Potentially, there could be a large demand for HHC products by individuals in Europe and internationally.

METHODS

Studies reporting HHC pharmacology, toxicology and analysis were identified from Pubmed and Scopus databases, and official international organizations' websites were considered.

RESULTS

HHC showed the effects of the typical cannabinoid on the central nervous system, with lower potency than Δ9-THC. A few studies highlighted that 9(R)-HHC is more potent than 9(S)-HHC. This molecule showed an affinity for cannabinoid receptor CB1 both in vitro and in vivo, suggesting a possible therapeutic effect in several pathologies. However, the affinity for the CB1 receptor suggests a possible addiction potential, inducing the users to misuse it. Since actual intoxication cases have not yet been reported, the HHC harmful potential was not described, probably due to the lack of effective analytical methods to detect HHC in biological matrices. Conversely, different analytical assays were developed and validated to separate HHC epimers in natural and non-natural sources.

CONCLUSION

Similarly to other NPS, the HHC represents a cheaper alternative to the controlled Δ9-THC. Its monitoring is a crucial challenge for toxicological and forensic purposes. To this concern, it is essential to further investigate HHC to support health providers in the identification of related intoxications.