How many types of cannabis are there?
This is a question that is frequently asked in cannabis circles. What this implies is that not all cannabis is the same. And if you have a tried a couple different cultivars you might have experienced varied effects with each; the difference might be as night and day.
Breeders have so far developed hundreds, if not thousands, of cannabis cultivars. How does one determine the effects that they will receive from one cultivar compared to the next? This can be only be answered by cannabis chemotyping.
What is Cannabis Chemotyping?
Chemotypes are distinct chemical phenotypes of cannabis (and other plants) that relate cannabinoid, terpene, and overall chemical composition. 
Cannabis chemotyping refers to the classification of cannabis cultivars based on their phytochemical characteristics. It also includes tallying the different chemical compounds and placing them in functional groups. Chemotypes describe the biochemical diversity of cannabis cultivars, which has applications in medical, recreational, and industrial fields of cannabis.
How is Chemotyping Done?
A traditional way of categorizing cannabis chemotypes was based on the amount of tetrahydrocannabinol (THC) or cannabidiol (CBD) produced by a cultivar. Based on this classification, THC-dominant chemotypes (type I) may produce intoxication while CBD dominant chemotypes generally do not (type III). A third category is a mixed or hybrid chemotype which produces varied effects based on the concentration of THC and CBD (type II). With this type of classification, consumers can predict a significant amount of the effects they are going to experience just by scrutinizing lab analysis reports where THC/CBD concentration is listed.  However, this is also influenced by other factors, including personal response, terpene profiles, and the ensemble effect.
Cannabis Chemotyping Goes Beyond THC and CBD
Recently, researchers have reported a novel way of chemotyping cannabis based on the terpenes present in a cultivar. [1,2]
Cannabis has over 150 different terpenes which add to the diversity of different cultivars.  In 2018, researchers analyzed 72 medical samples from different cultivar names (e.g., Blue Dream).  They came up with three main chemotypes based on the presence of about 19 detected terpenes.
They report that myrcene-dominant chemotypes are rich in myrcene and pinene; these included Pineapple Skunk, Kush Puppy, and Bob Marley, among 30 of the samples. The next chemotype is dominated by limonene and beta-caryophyllene. This chemotype housed 32 cultivars, including Lemon Sherbert and Jabberwocky. The last terpene-based chemotype is the terpinolene-dominant chemotype, which included 10 cultivars, such as Trainwreck. Interestingly, Blue Dream samples (4) showed up as two distinct chemotypes—myrcene/pinene (2) and limonene/beta-caryophyllene (2). 
Why Does It Matter?
Chemotyping helps us to understand the combinations of cannabis phytochemicals that produce different therapeutic effects. This can pave way for chemotypes with certain characteristics to be prescribed for specific medical conditions.
Chemotyping can also help to show relationships between different cultivars and hence the benefits that one would expect to achieve from each, such that a reproducible experience can be found.
Lastly, chemotyping can help to differentiate between hemp and cannabis cultivars. Legal hemp cultivars require that total THC be less than 0.3% of the total biomass.
- Fischedick JT. Identification of terpenoid chemotypes among high (-)-trans-Δ9– tetrahydrocannabinol-producing Cannabis sativa L. cultivars. Cannabis and Cannabinoid Research. 2017;2(1):34–47. Journal Impact Factor: n/a; Times Cited: 8
- Richins RD, et al. Accumulation of bioactive metabolites in cultivated medical Cannabis. PLOS ONE. 2018;13(7):e0201119. https://doi.org/10.1371/journal.pone.0201119. Journal Impact Factor: 2.740; Times Cited: 16
- Booth JK, Bohlmann J. Terpenes in Cannabis sativa – From plant genome to humans. Plant Sci. 2019;284:67-72. doi:https://doi.org/10.1016/j.plantsci.2019.03.022. Journal Impact Factor: 3.591; Times Cited: 30