Cannabis: THC, CBD, HHC and the Synthetic Cannabinoid Waves

The cannabis plant (Cannabis sativa L.) produces at least 113 identified cannabinoids, but the forensic chemist focuses on a handful of analytically and legally significant compounds. The biosynthesis begins in the secretory trichomes on the female flower surface. Geranyl pyrophosphate and olivetolic acid condense to form cannabigerolic acid (CBGA), the universal precursor. Specific synthase enzymes then convert CBGA into the carboxylic acid precursors of the three most important cannabinoids.

THCA synthase converts CBGA to THCA (tetrahydrocannabinolic acid). CBDA synthase converts CBGA to CBDA (cannabidiolic acid). CBCA synthase converts CBGA to CBCA (cannabichromenic acid). In the living plant, the carboxylic acid forms predominate; the neutral (decarboxylated) forms that are pharmacologically active accumulate through ageing, drying, and especially heating. This decarboxylation matters forensically: a freshly harvested plant has a very different THCA:THC ratio than dried and cured material, and heating the sample during extraction or analysis changes the ratio further.

Δ9-THC (tetrahydrocannabinol) is the primary psychoactive cannabinoid in marijuana. Its IUPAC name is (6aR,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromen-1-ol. The molecular formula is C21H30O2 with molecular weight 314.46 g/mol. CBD (cannabidiol) is the non-psychoactive cannabinoid that has driven the hemp industry and pharmaceutical development; it is a regioisomer of THC with the same molecular formula but a different arrangement of the double bond and the cyclohexene ring. CBN (cannabinol) is an oxidation product of THC that accumulates as cannabis ages; high CBN relative to THC is a qualitative marker of old or degraded material.

The THC:CBD ratio is a key botanical marker. Drug-type cannabis (marijuana) typically has THC far exceeding CBD, often in a ratio of 5:1 to 20:1. Hemp and CBD-dominant varieties have CBD exceeding THC, often 10:1 or higher. This ratio, measured by GC-MS or HPLC after extraction, is the analytical basis for hemp-vs-marijuana determination under both the USDA Farm Bill 2018 threshold and EU Regulation 2021/2115.

The 0.3 per cent THC threshold was first proposed in 1976 by Ernest Small and Arthur Cronquist in their taxonomic revision of Cannabis, as an arbitrary but reproducible line between drug-type and fibre-type varieties. It entered US law via the Agricultural Improvement Act of 2018 (the Farm Bill), which redefined hemp as Cannabis sativa L. with not more than 0.3 per cent Δ9-THC on a dry-weight basis. The same threshold was adopted in EU agricultural regulations for hemp cultivation. Canada sets 0.3 per cent as a licensing threshold for industrial hemp under the Industrial Hemp Regulations SOR/2018-145. Switzerland uses 1.0 per cent as its threshold, an outlier among major jurisdictions.

The measurement challenge is substantial. The 0.3 per cent limit refers specifically to Δ9-THC, the neutral decarboxylated form. But in fresh plant material, THCA dominates. A forensic laboratory must decide whether to report only Δ9-THC, or to convert THCA to THC equivalents using the decarboxylation conversion factor (THCA × 0.877 + Δ9-THC = total potential THC). The USDA's Agricultural Marketing Service interim rules for hemp testing require the total THC calculation (acid plus neutral form), which substantially changes the classification outcome for borderline samples.

Under India's NDPS Act 1985, the framework is structurally different. The Act separately schedules: ganja (the flowering or fruiting tops of the female cannabis plant), charas (the resin extracted from the plant), and hemp (the mature stalk, seeds, and leaves with no flowering tops). The Act does not set a numerical THC threshold; instead, the identity of the plant part determines legality. This creates different analytical challenges: the chemist must characterise the morphological identity of the material (is this flowering tops or mature stalk?) in addition to, or in some cases instead of, measuring THC content. The Punjab and Haryana High Court judgment in Satpal v. State (2016) addressed this distinction in the context of hemp cultivation in Himachal Pradesh.

In the UK under the Misuse of Drugs Act 1971, cannabis is a Class B controlled substance regardless of THC content. Cultivation licences for industrial hemp (not exceeding 0.2 per cent THC) are issued by the Home Office under a specific exemption. The threshold here is 0.2 per cent, differing from the USDA 0.3 per cent, and is applied to licensed cultivation only; seized material is simply cannabis unless the cultivator holds a valid licence.

India has a millennia-long cultural relationship with cannabis. The NDPS Act 1985 recognises three distinct preparations. Ganja refers to the flowering or fruiting tops of the female plant, whether cultivated or wild, and constitutes the controlled substance at the centre of most NDPS cannabis seizures in India. The controlled substances scheduling framework covers the NDPS quantity bands for ganja and charas and how they interact with the chemist's quantitative reporting obligations. Charas is the separated resin obtained from the cannabis plant, including concentrated preparations and hashish. The Act defines hemp (referred to in the Act as bhang in common usage, though the Act's text uses "cannabis plant") as the leaves, seeds, and mature stalk after separation of the resin; this is not scheduled under the main drug control provisions but may be regulated under state excise laws.

Bhang is widely prepared and consumed in India, particularly during Holi and the Mahashivratri festival, as a drink made from cannabis leaves ground with milk, spices, and sugar. It occupies an ambiguous legal position: since it uses leaves rather than flowering tops, it falls outside the strict ganja definition in the NDPS Act and is therefore regulated at the state level, with some states (including Rajasthan and Uttar Pradesh) permitting its licensed sale. Laboratories receiving bhang seizures must report the plant parts present and their THCA/THC profile to assist prosecutors in establishing whether the seized material falls under the NDPS ganja definition.

Charas (hashish) seized in India is predominantly from Himalayan traditional cultivation zones (Malana in Himachal Pradesh, the Parvati Valley) or from Afghan import routes. It typically presents as compressed resin blocks or hand-rolled cylinders (the traditional "Malana cream" format). Afghan hashish tends to have a different terpene and cannabinoid profile from Indian charas, reflecting distinct plant genetics and preparation methods; GC-MS terpene profiling can contribute to origin attribution, though it cannot be conclusive without a large validated reference database.

Internationally, hashish encountered in the UK and European markets is predominantly North African (Moroccan pollen hash being the dominant product), with Afghan varieties also prevalent in continental Europe. The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) 2023 Drug Markets Report documented average THC content in European hash seizures of 18 to 28 per cent, considerably higher than 1990s levels, reflecting selective cultivation.

Hexahydrocannabinol (HHC) is a hydrogenated form of THC. Replacing the 9-10 double bond of Δ9-THC with two hydrogen atoms (reduction, typically using catalytic hydrogenation) produces HHC, which exists as two diastereomers: (9R)-HHC (the pharmacologically active form, sometimes called 9R-HHC or (+)-HHC) and (9S)-HHC (the less active form). HHC was first synthesised by Roger Adams in 1944. In the modern context, HHC is produced from CBD via acid-catalysed isomerisation to Δ8-THC or Δ9-THC as an intermediate, followed by catalytic hydrogenation; this means that HHC derived from hemp CBD is being marketed in the US and some EU member states as a legal alternative to THC, because it is not explicitly named in the federal Controlled Substances Act and is not Δ9-THC.

Δ8-THC (delta-8-tetrahydrocannabinol) is a naturally occurring but trace-level cannabinoid in cannabis, typically present at well below 1 per cent in natural material. It is a positional isomer of Δ9-THC, differing only in the position of the double bond. Δ8-THC has approximately 60 to 70 per cent of the potency of Δ9-THC at the CB1 receptor and produces qualitatively similar psychoactive effects. Like HHC, it can be produced in large quantities from hemp CBD by acid-catalysed isomerisation, making it a commercially viable product from legally grown hemp.

The analytical challenge is formidable. GC-MS methods tuned for Δ9-THC must be confirmed with appropriate reference standards (available from Cerilliant, Cayman Chemical, and NIST SRM 3405 series) to correctly differentiate Δ8-THC, Δ9-THC, Δ10-THC, and HHC. The mass spectra of these isomers are similar because all have the same molecular formula (C21H30O2) and very similar fragmentation pathways; the key diagnostic ions and retention time relative to an internal standard are the distinguishing features. The DEA has issued guidance asserting that synthetically derived Δ8-THC and HHC remain Schedule I controlled substances regardless of origin (CBD from hemp), a position contested in several US federal court cases as of 2024.

In the UK, HHC was added to the Misuse of Drugs Act 1971 Class B schedule via a Statutory Instrument in September 2023, making the UK one of the first jurisdictions to explicitly schedule HHC as a standalone compound. Germany banned HHC under the Neue-psychoaktive-Stoffe-Gesetz (NpSG), with the ban taking effect on 27 June 2024. In India, the NDPS Act's broad definition of THC-containing preparations means that HHC and Δ8-THC products would likely fall within scope, though no specific case law had been tested as of early 2024.

Synthetic cannabinoids (SCs) are a chemically diverse class of molecules that share the ability to bind and activate the CB1 and CB2 receptors, producing cannabis-like effects. Unlike THC, they are fully synthetic, are not derived from the cannabis plant, and in many cases bind CB1 with much higher affinity and efficacy than THC, producing more intense and more dangerous effects including acute psychosis, cardiovascular toxicity, acute kidney injury, and fatalities.

The first wave (approximately 2004 to 2011) was dominated by the JWH (John W. Huffman) series, developed by Huffman's research group at Clemson University as pharmacological tools. JWH-018 (1-pentyl-3-(1-naphthoyl)indole) was the prototypical first-wave compound. JWH-073, JWH-081, JWH-122, JWH-200, and JWH-250 followed. These compounds share an indole core with a naphthoyl or phenyl group at the 3-position and an alkyl chain at the N-position. K2 and Spice products, seized in European markets from 2008 and in the US from 2009, were largely spice-blend plant material with JWH-018 and JWH-073 sprayed on. The US banned five JWH compounds under the Emergency Scheduling Act in 2011.

The second wave (approximately 2011 to 2014) arose as clandestine chemists responded to the JWH scheduling by substituting the naphthoyl ring with fluorinated variants (AM-2201, bearing a fluoropentyl chain instead of a plain pentyl chain on JWH-018), moving from indole to indazole cores, and introducing UR-144 and XLR-11 (the fluorinated variant of UR-144). AM-2201 produced a serious public health event in Nottingham, UK, in 2011, when dozens of users were hospitalised after smoking products later confirmed by Forensic Science Service laboratories to contain AM-2201.

The third wave (approximately 2014 to present) is characterised by the FUBINACA and FUBICA scaffolds, which are structurally distinct from the classic JWH indole-naphthoyl frame. AB-FUBINACA, ADB-FUBINACA (also called AMB-FUBINACA or MAB-FUBINACA), and AB-PINACA are valine-amine and alanine-amine derivatives of the indazole carboxamide scaffold. AMB-FUBINACA (methyl 2-[1-(4-fluorobenzyl)-1H-indazole-3-carboxamido]-3-methylbutanoate) was identified in New York in 2016 in association with a mass-poisoning event in Brooklyn that intoxicated 33 people, of whom 18 were hospitalised, prompting widespread media attention to what was initially called a "zombie drug." EMCDDA's Early Warning System tracked more than 160 novel synthetic cannabinoids between 2015 and 2022.

Structural modification follows a predictable cycle: a scheduling authority adds a compound (or a class defined by a structural feature) to a controlled substances list; within months, a new compound appears in which one functional group has been changed, typically a halogen substitution (F for Cl), an alkyl chain shortened or lengthened by one carbon, or a methyl group repositioned, placing it outside the specific schedule entry. Forensic laboratories respond by adding new reference standards and updating their LC-MS/MS inclusion lists, but remain one compound behind clandestine synthesis.

For bulk cannabis plant material, the presumptive analytical workflow begins with macroscopic botanical examination (cystolithic hairs, resin glands) and the Duquenois-Levine test. This colour test involves three sequential reagents: vanillin in ethanol with hydrochloric acid, concentrated hydrochloric acid extraction, and chloroform extraction. THC reacts to produce a purple-violet colour in the chloroform layer; the test has high specificity for cannabis and is accepted as a presumptive positive under SWGDRUG guidance and by the Home Office Forensic Regulator in the UK. It is not specific to THC at the structural level; it responds to several other cannabinoids but not to synthetic cannabinoids, which do not contain the phenolic resorcinyl ring system that drives the reaction.

For GC-MS confirmation of natural cannabis, the standard method involves solvent extraction (typically methanol, chloroform, or ethanol) followed by GC-MS analysis on a 5% phenylmethyl polysiloxane column. The decarboxylation that occurs during the high GC injector temperature (250 to 280°C) converts THCA to THC, so a GC-MS analysis reflects mostly THC even in fresh material. This is actually a feature, not a bug, for legal threshold determination in jurisdictions that count decarboxylated THC. For acid-form analysis (THCA quantification), HPLC-UV or LC-MS/MS at ambient temperature preserves the acid forms and allows separate quantification of THCA and THC.

For synthetic cannabinoids, GC-MS can detect and identify the early JWH-series compounds, which are reasonably thermally stable. However, third-wave compounds (AB-FUBINACA, ADB-PINACA series) can undergo thermal decomposition in the GC injector, producing artefact peaks that obscure identification. LC-MS/MS is the method of choice for third-wave SCs: atmospheric-pressure ionisation (positive ESI or APCI) with tandem mass spectrometry provides molecular weight confirmation and characteristic product ion spectra. The DEA's Special Testing and Research Laboratory (STRL) and the EMCDDA's reference laboratory network (EU-REITOX) both operate LC-MS/MS workflows with continuously updated spectral libraries for novel SC identification.

1. Macroscopic examination
   Examine the exhibit under 10x loupe or stereomicroscope. Cannabis plant material shows cystolithic trichomes (calcium oxalate crystals inside hair cells), resin glands (capitate-stalked trichomes on female flower material), and characteristic leaf morphology. Document and photograph before sampling.
2. Duquenois-Levine presumptive test
   Add a small amount of plant material (1-5 mg) to a spot plate well. Add 5 drops of Duquenois reagent (vanillin, acetaldehyde, ethanol, HCl), then 5 drops concentrated HCl, shake. Add 5 drops chloroform. Cannabis: purple-violet colour in chloroform layer. Negative: yellow-orange or no colour transfer. Document result per SWGDRUG presumptive test SOP.
3. Solvent extraction
   Weigh representative sub-sample. Extract with methanol or chloroform (1 mL per 10 mg plant material). Vortex 2 minutes, centrifuge. Dilute extract 1:10 to 1:100 for GC-MS injection. Prepare duplicate.
4. GC-MS confirmation
   Inject on DB-5 or HP-5MS column (30m x 0.25mm x 0.25 μm). Temperature programme: 60°C hold 2 min, 10°C/min to 300°C, hold 5 min. EI ionisation at 70 eV. THC: RT approximately 15-17 min depending on column, base peak m/z 314, characteristic fragments at m/z 299, 231, 193. Compare against NIST library and in-house certified reference standard.
5. Synthetic cannabinoid screening (if GC-MS negative for natural cannabinoids)
   Switch to LC-MS/MS workflow. Positive ESI, MRM transitions from validated inclusion list for current EMCDDA or UNODC SCs. Extract with acidified acetonitrile. Submit for NPS reference laboratory confirmation if a novel compound is suspected (no library match).
6. Quantification and reporting
   For hemp-vs-marijuana determination: quantify THCA and Δ9-THC by HPLC-UV or LC-MS/MS against certified reference standards (Cerilliant, USP). Calculate total THC: (THCA x 0.877) + Δ9-THC. Report against 0.3% dry-weight threshold per jurisdiction. For NDPS reporting, state plant parts identified and controlled substance confirmed.