Chemical Classification — Modern Science Replacing Indica/Sativa
1. Why Classify by Chemotype?
The Indica/Sativa/Ruderalis system was created in the 18th century (Lamarck, 1785) based on morphology — height, leaf shape, flower density. However, after over 100 years of crossbreeding, the morphological boundaries between “subspecies” have virtually disappeared.
A chemical analysis of 89,923 commercial cannabis flower samples from six US states (Smith et al., 2022) found that “Indica”, “Sativa” and “Hybrid” labels do not consistently match a plant’s actual cannabinoid or terpene composition. In other words, you cannot tell how much THC or CBD a strain contains just by looking at its leaves.
Chemotype — classification based on chemical composition — solves this problem. The system proposed by Small & Beckstead (1973) and later extended by de Meijer et al. (2003) divides cannabis into chemotypes measurable by HPLC or GC-MS.
2. The Five Main Chemotypes
| Chemotype | THC:CBD Ratio | Primary Cannabinoid | Applications |
|---|---|---|---|
| Type I | High THC >5:1 | THC 15-35% | Medical (pain, insomnia, PTSD) |
| Type II | Balanced 1:1-5:1 | THC+CBD similar | Medical (reduced psychoactive side effects) |
| Type III | High CBD <1:5 | CBD 10-20%, THC<1% | Wellness, legal hemp |
| Type IV | High CBG | CBG 10-20% | Research, anti-inflammatory |
| Type V | No cannabinoids | <0.1% | Fiber, food, construction |
3. THCAS vs CBDAS Gene — The Chemotype Determinant
Chemotype is primarily determined by a single gene locus on the chromosome encoding synthase enzymes:
- THCAS (THCA synthase) — converts CBG-A → THC-A
- CBDAS (CBDA synthase) — converts CBG-A → CBD-A
| Genotype | Chemotype | Result |
|---|---|---|
| BT/BT | Type I | High THC, virtually no CBD |
| BT/BD | Type II | Both THC and CBD |
| BD/BD | Type III | High CBD, virtually no THC |
Key point: Broad or narrow leaf shape is NOT related to THCAS/CBDAS genes. Only genetic testing or chemical analysis can accurately determine chemotype.
4. Over 150 Cannabinoids — Beyond THC and CBD
As of 2025, scientists have identified over 150 phytocannabinoids in cannabis:
| Cannabinoid | Origin | Research Potential |
|---|---|---|
| CBN | THC degradation | Sleep aid |
| CBC | From CBCA synthase | Anti-inflammatory, antidepressant |
| THCV | African strains | Appetite suppression, anti-diabetic |
| CBDV | Hemp varieties | Epilepsy, autism |
| CBG | Precursor to all cannabinoids | Antibacterial, anticancer |
| Delta8-THC | THC isomer | ~50% less potent |
5. Terpene Profile & Entourage Effect
Cannabis produces over 200 terpenes. Russo (2011, 2019) proved that terpenes interact synergistically with cannabinoids — called the “entourage effect”
| Terpene | Aroma | Biological Effect | Entourage |
|---|---|---|---|
| Myrcene | Mango, herbal | Sedative, muscle relaxant | Enhances THC absorption through BBB |
| Limonene | Citrus | Anxiolytic, mood elevator | THC+Limonene reduces anxiety |
| Beta-Caryophyllene | Black pepper | Anti-inflammatory | Binds CB2 receptor directly |
| Linalool | Lavender | Sedative, anticonvulsant | Enhances CBD seizure reduction |
| Alpha-Pinene | Pine | Bronchodilator, focus | Counteracts THC memory impairment |
| Terpinolene | Floral, pine | Mildly sedative | Found in “Sativa” varieties |
| Humulene | Hops | Appetite suppressant | Anti-inflammatory with CBC |
| Ocimene | Basil | Antifungal, antiviral | Needs more research |
Practical implication: Two Type I strains (both THC 25%) with different terpene profiles will produce entirely different effects.
6. Autoflower Has Reached Photoperiod Quality
Modern breeding programs (2020-2026) crossed Ruderalis genes into elite photoperiod genetics through 5-8 generations of backcross:
- THC autoflower now reaches 25-30% (equivalent to photoperiod)
- CBD autoflower: Type III achieving 15-20% CBD, THC < 0.3%
- Life cycle 70-90 days → 4 harvests/year outdoors
- No photoperiod dependency → year-round cultivation in tropics
7. Strain Selection Guide by Chemotype
Instead of asking “Indica or Sativa?” start with: “What chemotype do I need?”
5-Step Selection Process:
- Identify the chemotype needed (Type I-V) based on purpose
- Select appropriate terpene profile to fine-tune effects
- Verify COA from third-party laboratory
- Beginners → start with Type II or Type III
- Keep a usage journal to find your optimal formula
References
- Small & Beckstead (1973). Nature, 245, 147-148.
- Russo (2011). British J Pharmacology, 163(7), 1344-1364.
- Russo (2019). Frontiers in Plant Science, 9, 1969.
- Laverty et al. (2019). Genome Research, 29, 146-156.
- Grassa C.J. et al. (2021). A new Cannabis genome assembly associates elevated cannabidiol (CBD) with hemp introgressed into marijuana. New Phytologist, 230(4), 1665-1679. doi:10.1111/nph.17243
- Smith C.J., Vergara D., Keegan B., Jikomes N. (2022). The phytochemical diversity of commercial Cannabis in the United States. PLOS ONE, 17(5), e0267498. doi:10.1371/journal.pone.0267498
- ElSohly M.A., Radwan M.M., Gul W., Chandra S., Galal A. (2017). Phytochemistry of Cannabis sativa L. Progress in the Chemistry of Organic Natural Products, 103, 1-36. doi:10.1007/978-3-319-45541-9_1
- Morales P., Hurst D.P., Reggio P.H. (2017). Molecular Targets of the Phytocannabinoids: A Complex Picture. Progress in the Chemistry of Organic Natural Products, 103, 103-131. doi:10.1007/978-3-319-45541-9_4
- de Meijer et al. (2003). Genetics, 163(1), 335-346.
- Vergara et al. (2021). PeerJ, 9, e10672.
- Tahir et al. (2021). J Cannabis Research, 3, 7.
Legal Disclaimer: This article is for educational purposes only. In Thailand, cannabis is regulated under the Notification of the Ministry of Public Health Re: Controlled Herbs (Cannabis), B.E. 2568 and Ministerial Regulation B.E. 2569. Commercial sale, processing and export of cannabis flower require a licence; PT 33 (ภ.ท. 33) is the prescription form for dispensing cannabis flower, not a cultivation permit. Recreational use is prohibited.
Asiannabis Community — asiannabisthailand@gmail.com