How Cannabis Strain Genetics Influence the THC:CBD Ratio

Whydo strains like Blue Dream and Harlequin have such different effects? In large part, its because they have very different THC-to-CBD ratios.

THC and CBD are the two most abundant cannabinoids in most strains. THC is well known as the major psychoactive compound. CBD is best known for having a wide range of medical uses. While CBD lacks the psychoactive properties of THC, it does influence the effects of THC in the brain. This is why the THC:CBD ratio strongly influences a strains effects, and why that ratio is important when deciding which strain is right for you.

Heres the cool part: The THC:CBD ratio is largely determined by strain genetics. Each plants genetic code determines the way the plant produces the two compounds. Its a fascinating process that many consumers arent aware of.

THC and CBD are both made from another cannabinoid called cannabigerol (CBG). Within Cannabis plants, each of these compounds is actually present in a slightly different, acidic form. The plants are really making either THCA or CBDA out of CBGA (Figure 1). Its only after THCA and CBDA are decarboxylatedby heat that we get significant levels of THC and CBD. The heat energy from your vaporizer, lighter, or oven causes a chemical reaction that turns THCA and CBDA into THC and CBD, respectively.

THCA and CBDA dont have the same effects as their activated (decarboxylated) counterparts. Remember that scene in Super Trooperswhere the guy eats a bag of cannabis flower and goes out of his mind? That wouldnt really work, because flower contains mostly THCA, which isnt psychoactive. You would have to heat the flower at the right temperature first, turning the THCA into THC, before eating it would get you high.

A single CBGA molecule can turn into a single THCA or CBDA molecule, but not both. How does the plant decide which to make? That depends on the presence of an enzyme that comes in two flavors. Lets call them Enzyme 1 (E1) and Enzyme 2 (E2).

E1 takes CBGA and converts it into CBDA, while E2 converts CBGA into THCA (Figure 1). Some strains only have E1, some only have E2, and some have both.

Like most plants and animals, Cannabis plants inherit two copies of their genes (although there are rare exceptions to this). As it turns out, the E1 and E2 enzymes that turn CBGA into either CBDA or THCA are encoded by two different versions of the same gene. Because each plant gets two copies of that gene, there are only three possibilities: A plant can have two copies of the gene that encodes the E1 enzyme, it can have one copy each of the genes that encode E1 and E2, or it can have two copies of the gene that encodes E2 (Figure 2).

Importantly, these three possibilities are based solely on the THC:CBD ratio, and dont take into account other compounds that a particular strain might produce. The three broad THC:CBD ratio strain categories are:

Cannabis genetics limit THC and CBD production so that only these three broad categories of flower are possible. Hemp strains do not produce significant levels of THC, while most commercial strains fall into the high-THC categorythey have THC but negligible levels of CBD. Mixed strains produce both THC and CBD, but generally not as much THC as high-THC strains or as much CBD as the more potent hemp strains.

In the next article of this series, we will explore more precisely what the limits on THC and CBD levels are for each of these categories. Later on, well consider some of the effects you may experience when consuming strains with different THC:CBD ratios.

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