Medical Research

Ernest Small and the Three Cannabis Chemotypes

Written by Shawn Tucker

Dr. Ernest Small, a principal research scientist at Agriculture and Agri-Food in Canada, shaped the landscape of cannabis with his book The Species Problem with Cannabis. It was this book that set the basis of 0.3 percent tetrahydrocannabinol (THC) as the distinguishing amount to separate hemp or (CBD) cannabidiol-dominant cannabis as type III of three different types based on cannabinoid content.


History of Cannabis Labeling

THC-dominant cannabis is labeled as type I and cannabis that has equal parts of THC and CBD is labeled as type II. Dr. Small further pointed out the differences between wild and domestic cannabis and argued that those varieties should include different labels specifically within his trio of types. [1] Although it can be argued that — at least in the United States — any wild cannabis is a result of escaped domestic cannabis and not truly a wild variant.

There has been much discussion and study on how to label cannabis. According to this 2021 study, “Cannabis breeders and users use vernacular ‘Sativa’ to describe cultivars with narrow leaflets and ‘Indica’ for cultivars with broad or wide leaflets, based on illustrations of Anderson, which deviated from the original botanical nomenclature.” [2] Until recently, there was not a significant amount of study done on the morphology of cannabis plants and whether or not it correlated to these labels.


Indica, Sativa, and Hybrid

However, the above mentioned 2021 study found visible leaf differences with 92 percent accuracy. “Traits usable as phenotype markers for CBD dominant cultivars included light-green and narrow leaflets, a greater number of primary and secondary serrations […].Traits for intermediate cultivars included deep-green and medium-wide leaflets, more primary and secondary serrations […]. Traits for THC dominant cultivars included deep-green and wide leaflets [and] large and compact inflorescences.” [2]

In a different study they found chemical differences in the three chemotypes that were tracked not only by cannabinoid content, but also by terpenes and flavonoids. “CBD-dominant strains had higher amounts of total CBD, cannabidivarin (CBDV), cannabichromene (CBC), α-pinene, β-myrcene, (−)-guaiol, β-eudesmol, α-eudesmol, α-bisabolol, orientin, vitexin, and isovitexin. Meanwhile, THC-dominant strains had higher total THC, total tetrahydrocannabivarin (THCV), total cannabigerol (CBG), camphene, limonene, ocimene, sabinene hydrate, terpinolene, linalool, fenchol, α-terpineol, β-caryophyllene, trans-β-farnesene, α-humulene, trans-nerolidol, quercetin, and kaempferol.” [3]

Since there is sufficient evidence that can differentiate at least type I and type III cannabis, perhaps the scientific community can agree to use other labels for these types. Providing clear definitions with solid scientific evidence gives the ability to differentiate for medical purposes, for testing levels of intoxication in consumers, and potentially for differentiating for political purposes surrounding legalization and taxation.




[1] Small, E. Evolution and Classification of Cannabis sativa (Marijuana, Hemp) in Relation to Human Utilization. The Botanical Review. 2015: 81, 189-294. doi:10.1007/s12229-015-9157-3. Times Cited=277. Journal Impact Factor=3.083


[2] Jin, D., Et al. Identification of Phenotypic Characteristics in Three Chemotype Categories in the Genus Cannabis. American Society for Horticultural Science 2021 56:4. Doi: 10.21273/HORTSCI15607-20. Times Cited=10. Journal Impact Factor=1.09


[3] Jin D., Et al. Identification of Chemotypic Markers in Three Chemotype Categories of Cannabis Using Secondary Metabolites Profiled in Inflorescences, Leaves, Stem Bark, and Roots. Frontiers in Plant Science 2021, 12: 699530. Doi: 10.3389/fpls.2021.699530. Times Cited=6. Journal Impact Factor=4.407

About the author

Shawn Tucker