How a Cannabis Plant Builds Cannabinoids and Terpenes
Cannabis sativa L. is one of the most chemically complex plants we cultivate. Scientists have isolated more than 1,600 compounds from Cannabis, including over 180 cannabinoids across 11 structural families. Add hundreds of terpenes on top of that- for example, a 2026 study of six cultivars identified 227 volatile terpenes alone. This series walks through that chemistry, from how the plant makes it to how it reaches the human body. We start at the beginning: biosynthesis, the plant's own assembly line.
Two building blocks meet
Every major cannabinoid starts from the same two parts.
A fatty-acid piece. The plant takes a six-carbon building block (hexanoyl-CoA) and adds three small two-carbon units to it. Two enzymes, tetraketide synthase and olivetolic acid cyclase, fold the result into a ring called olivetolic acid.
A terpene piece. Separately, the plant makes geranyl pyrophosphate (GPP), a 10-carbon molecule. It's the same starting material plants use to make monoterpenes like myrcene and limonene.
An enzyme called a prenyltransferase joins the two. The product is cannabigerolic acid (CBGA), often called the "mother cannabinoid," because nearly everything else branches off from it.
The fork in the road
What happens to CBGA next depends on which enzymes the plant makes:
THCA synthase turns CBGA into THCA.
CBDA synthase turns it into CBDA.
CBCA synthase turns it into CBCA.
THCA synthase and CBDA synthase are remarkably similar: their protein sequences are about 96% identical. Small differences in the enzyme's shape send the same starting molecule down a different path.
Two details often surprise people. First, the living plant makes cannabinoid acids, not THC or CBD. The familiar neutral forms mostly appear later, when the acids lose a carbon dioxide molecule through heat, light or time in storage. THC can also break down further into CBN as it ages. (We'll cover heat in detail later in this series.) Second, CBD does not turn into THC inside the plant. That conversion can
be done in a chemistry lab, but it doesn't happen in vivo.
The same machinery can also start from a shorter fatty-acid building block. When it does, it produces the "varin" cannabinoids, like THCVA and CBDVA, which have a shorter side chain and can behave differently in the body.
A parallel line for terpenes
Terpenes are made from the same five-carbon building blocks that feed GPP. Ten-carbon chains become monoterpenes; 15-carbon chains become sesquiterpenes like beta-caryophyllene. The final step is handled by a family of enzymes called terpene synthases.
Cannabis has a lot of them. A 2026 genome study identified 41 full-length terpene synthase genes, some of them able to make several different terpenes from one starting molecule. Some of these genes are highly active in the flowers of every cultivar, while others are switched on only in particular cultivars. That's a big part of why two plants of the same species can smell completely different.
Where it all happens
Almost all of this chemistry takes place in glandular trichomes, the tiny resin glands that frost the flowers. A 2020 study found that the large stalked trichomes on mature flowers have 12 to 16 secretory cells, carry high cannabinoid levels and lean heavily toward monoterpenes. Smaller sessile trichomes have about eight secretory cells and a different terpene mix. Trichomes get their own post next.
Why this matters
Genetics sets the chemistry. In a classic 2003 study, Etienne de Meijer and colleagues crossed pure-THC and pure-CBD plants. Every first-generation plant had a mixed THC-CBD profile. In the next generation, pure-CBD, mixed and pure-THC plants appeared in a 1:2:1 ratio. They explained it with a single genetic locus with two co-dominant forms, one tied to CBD and one to THC. Growing conditions influence how much a plant makes, but its genes decide what it can make. A specific chemical profile starts with the right genetics, kept true to type.
The plant is also a library of chemistry that science hasn't finished reading. The pathway is now understood well enough that in 2019, Jay Keasling's lab rebuilt it in yeast, producing CBGA, THCA, CBDA, THCVA and CBDVA from simple sugar. Feeding the yeast different fatty acids even produced cannabinoid analogues that don't occur in nature. Yet the plant still holds the full picture. Researchers note that cannabis resin contains hundreds of terpenes and cannabinoids, many not yet conclusively identified, and that our understanding of what controls them is still rudimentary. Every distinct cultivar is a unique combination of these genes. Preserving clean, documented genetics preserves chemistry that may prove valuable as the science catches up.
And it all starts small. The compounds people study, consume and debate all begin as a few enzymes working inside glands smaller than a grain of sand.
What we still don't know
Biosynthesis of the major cannabinoids is fairly well mapped, but there are still many gaps, especially for the minor cannabinoids. Researchers also lack a full picture of how the plant regulates terpene and cannabinoid production, and how much of the variation between cultivars comes from genetics versus environment.
Next in the series: trichomes, the factories on the flower.
Sources
Tahir, M.N., Shahbazi, F., Rondeau-Gagné, S., Trant, J.F. (2021). The biosynthesis of the cannabinoids. Journal of Cannabis Research, 3, 7. https://doi.org/10.1186/s42238-021-00062-4
Luo, X., Reiter, M.A., d'Espaux, L., Wong, J., et al. (2019). Complete biosynthesis of cannabinoids and their unnatural analogues in yeast. Nature, 567, 123–126. https://doi.org/10.1038/s41586-019-0978-9
de Meijer, E.P.M., Bagatta, M., Carboni, A., Crucitti, P., et al. (2003). The inheritance of chemical phenotype in Cannabis sativa L. Genetics, 163(1), 335–346. https://doi.org/10.1093/genetics/163.1.335
Booth, J.K., Bohlmann, J. (2019). Terpenes in Cannabis sativa: from plant genome to humans. Plant Science, 284, 67–72. https://doi.org/10.1016/j.plantsci.2019.03.022
Mi, Y., Zhang, M., Zhang, K., Li, J., et al. (2026). Expansion and functional diversification of terpene synthases shape volatile terpenoid landscape in Cannabis sativa. Acta Pharmaceutica Sinica B, 16(8), 5487–5503. https://doi.org/10.1016/j.apsb.2026.03.035
Livingston, S.J., Quilichini, T.D., Booth, J.K., Wong, D.C.J., et al. (2020). Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. The Plant Journal, 101(1), 37–56. https://doi.org/10.1111/tpj.14516
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