Chemovar classification: the chemotype I–V system

TL;DR

• 5 chemotypes (I–V) instead of Indica/Sativa classify cannabis by cannabinoid ratio.
• A single gene locus with two alleles drives the THC:CBD ratio.
• Type II (mixed) follows a classic 1:2:1 Mendelian segregation in crosses.
• Chemovar = chemotype + dominant terpene profile — a more precise classification than strain name.

How does the B_D/B_T allele model work?

De Meijer et al. (2003) showed the THC:CBD ratio is largely controlled by a single locus with two alleles: B_D encodes functional CBDA-synthase, B_T functional THCA-synthase. A plant with two B_T alleles (B_T/B_T) is chemotype I (THC-dominant), B_D/B_D is chemotype III (CBD-dominant), and the heterozygous combination B_D/B_T yields chemotype II with a mixed profile. Crossing two chemotype-II parents produces classic 1:2:1 segregation in offspring — a rare example of simple Mendelian inheritance for a complex chemical trait.

What is a 'chemovar' as distinct from a strain name?

The term chemovar (chemical variety) combines chemotype (cannabinoid ratio) with the dominant terpene profile, e.g. 'chemotype I, myrcene-dominant'. Hazekamp et al. (2016) propose this system because it is reproducibly lab-measurable, whereas names like 'OG Kush' can carry entirely different chemical profiles between breeders. For consumers and medical professionals, the chemovar is therefore a more informative label than the brand name.

Why do this site's 91 strain profiles still show a name?

Strain names remain entrenched for marketing and recognition, and are therefore kept here, but as an indicative reference rather than a guarantee. Where available, lab values (THC/CBD percentage range, top-3 terpenes) supplement the actual chemovar information. Anyone seeking a reliable chemical profile should primarily consult the current batch's certificate of analysis (COA) rather than the name.

Swiss regulation and the chemotype limit

In Switzerland, the limit of one percent total THC determines the legal classification of cannabis products. This strict separation divides biological chemotypes into two regulatory classes. While chemotype I (THC-dominant) and chemotype II (mixed type) fall under the Narcotics Act due to their elevated THC content, chemotype III (CBD-dominant) as well as the rarer types IV and V are legally available as industrial hemp or CBD products. For consumers and producers in Switzerland, this biological classification is therefore of existential importance to avoid legal consequences in everyday life.

Since August 2022, access to medical applications in Switzerland has been simplified, as doctors can prescribe medical cannabis directly. Standardized chemovars play a central role here, as medical cannabis must be dosed precisely. The ongoing cantonal pilot trials also use this scientific classification to research controlled distribution. In road traffic, however, a strict zero-tolerance practice applies with a limit of 1.5 micrograms of THC per liter of blood, which is why even the consumption of chemotype III flowers can lead to unfitness to drive due to minimal traces of THC.

• A total THC limit of less than one percent determines legality in everyday Swiss life.
• Chemotype III enables legal production and acquisition without narcotics status.
• Medical prescriptions of medical cannabis use chemovar profiles for precise therapy planning.
• Pilot trials in Swiss cities investigate the regulated sale of defined chemotypes.
• Strict zero tolerance in road traffic requires caution with all chemotypes with measurable THC levels.

Influence of terpenes on chemovar determination

While the chemotype exclusively describes the ratio of the main cannabinoids, the complete chemovar also encompasses the terpene profile of a plant. Terpenes are volatile organic compounds responsible for the characteristic aroma and taste of the flowers. They are produced in the glandular trichomes of the plant and vary greatly depending on genetics and environmental conditions. Only through the combination of the specific cannabinoid ratio and dominant terpenes such as myrcene, limonene, or beta-caryophyllene can a plant be precisely characterised and distinguished from other batches.

Determining the terpene profile is essential for pharmaceutical and scientific classification, as these substances can influence the overall effect of the plant. In scientific literature, this interaction is frequently studied because terpenes can modulate the absorption of cannabinoids. A chemovar certificate therefore lists the percentages of the most important terpenes alongside the cannabinoid concentrations. Without this detailed analysis, any classification remains incomplete, as two plants of the same chemotype can exhibit completely different properties in practical application due to different terpenes.

• Terpenes complement the cannabinoid ratio for the complete identification of a chemovar.
• Dominant terpenes such as myrcene, limonene, and linalool shape the biological profile.
• Laboratory analyses standardly record the terpene spectrum for medical applications.
• The interaction between terpenes and cannabinoids influences the pharmacological properties.

Laboratory analysis and the Certificate of Analysis (COA)

The exact determination of a chemovar is only possible through modern laboratory analysis, which goes far beyond simple visual assessments. The most important document in this process is the Certificate of Analysis, or COA. High-performance liquid chromatography is used to measure the exact concentrations of acidic forms and neutral cannabinoids. This analysis is necessary because the naked eye or smell do not allow for reliable conclusions regarding the exact ratio of THC, CBD, or CBG. Only a certified laboratory can confirm the chemical identity of a batch beyond doubt.

For producers and distributors in Switzerland, this analysis is legally required to prove compliance with the THC limit. Sampling and analysis must follow standardised procedures to deliver reproducible results. In addition to cannabinoids, a complete COA also records potential residues of pesticides, heavy metals, or moulds. For consumers, the COA provides the only assurance that the purchased product actually corresponds to the declared chemovar and is free from undesirable contaminants, which is of the highest priority, especially in the medical sector.

• High-performance liquid chromatography determines the exact active ingredient concentrations in the laboratory.
• The Certificate of Analysis seamlessly documents the chemical profile of each batch.
• Legal requirements demand proof of the THC content to comply with the limit values.
• Laboratory testing for contaminants ensures the purity and quality of the analyzed flowers.

Challenges in stabilizing chemovars

Breeding and stabilizing a specific chemovar presents breeders with major biological challenges. Since cannabis is a dioecious plant, it tends to exhibit high genetic variability during sexual reproduction. Even if the parent plants have a clear chemovar profile, the offspring in the next generation can deviate significantly. To guarantee a homogeneous profile, breeders must select over several generations or resort to vegetative propagation using cuttings. This is the only way to ensure that each plant stably develops the desired ratio of active ingredients.

In addition to genetics, environmental factors such as light spectrum, temperature, nutrient supply, and humidity also play a decisive role in the expression of the chemovar. This so-called phenotypic plasticity means that the same genetics produce varying cannabinoid and terpene concentrations under different growing conditions. For standardized production, especially in the medical sector, a strictly controlled indoor environment is therefore essential. Only through the combination of stable genetics and constant environmental conditions can a chemovar be reproducibly cultivated across different batches.

• Without strict selection, sexual reproduction leads to genetic segregation of the profiles.
• Vegetative propagation using cuttings ensures the preservation of identical chemovars.
• Environmental factors such as light and temperature influence the actual concentration of active ingredients.
• Controlled indoor facilities are necessary for the production of consistent medical profiles.

FAQ