Terpenes and related terpenoid compounds constitute the most diverse class of plant natural products. Terpenoids are compounds with terpene moieties linked to other moieties derived from different biosynthetic pathways. This class of molecules plays a role in both primary and secondary plant metabolism, facilitating diverse metabolic and ecological functions. In fact, at least 30,000 distinct terpenoids have been identified to date. Although the angiosperms (flowering plants) are an exceptionally rich reservoir of terpenoid diversity, all cellular life utilizes terpenoid compounds in one way or another. For example, humans synthesize the essential vitamin A from b-carotene, the orange-hued terpenoid that gives carrots their distinct color.
I consistently read and hear about how the aroma of cannabis is due to terpenes. A quick web search of just the term “terpene” returns mostly results attributing the aroma of cannabis to terpenes. Common lore suggests that not only do terpenes provide those wonderful and varied cannabis flower aromas, but they also cause some of the “effect” of consumption. The online and in-person cannabis consumer information experience is filled with charts and expert advice making such links as myrcene enhances relaxation, or limonene acts as an antidepressant.
So is there really scientific evidence to support the common cannabis terpene claims? The first question I wanted to address is whether or not your olfactory system is detecting solely terpenes when you smell your favorite cannabis flower or concentrate.
After reviewing the available scientific literature, my conclusion is that aromatic terpenes are a component of cannabis aroma, but not the sole source. Several lines of evidence lend support to the complexity of cannabis aroma.
For one, it’s a fact that not all plant aromas are derived from terpenes. For example, cinnamaldehyde, the compound responsible for cinnamon smell and taste, is as its name implies an aldehyde, not a terpene. Although I’ve never encountered cinnamon tasting notes in cannabis flower, consider the sweet aromas of strawberry, bananas, and pears that are sometimes found in cannabis. These are due to esters, such as butyl acetate. Sirius J at High Times published an interesting article about esters and aroma in cannabis back in 2016, which is worth a read:
Esters: the secrets behind the sweet aromas of cannabis
The 1996 study conducted at the University of Mississippi cited in the High Times article about esters is the only peer-reviewed research I can find regarding the non-terpene fraction of volatile cannabis oil. In the four samples they tested, the range of compounds classified as esters or ketones was 0.68% – 2.87% by weight. So while terpenes are a large fraction of the volatile cannabis oils that were extracted in this study, other classes of molecules that likely contribute to aroma were also present.
In conclusion, terpenes and terpenoids are a diverse class of molecules that constitute many of the common botanical aromas and flavors humans can sense with their olfactory and gustatory (taste) sensory systems. However, plant aromas and flavors are typically the consequence of a complex blend of various molecules, including but not limited to terpenes and terpenoids. Cannabis flowers do contain significant fractions of terpenoids, but these are not the sole source of aroma and flavor.
Ross S.A. and ElSohly M.A. (1996) The Volatile Oil Composition of Fresh and Air-Dried Buds of Cannabis sativa. Journal of Natural Products. 59:1, 49-51 DOI: 10.1021/np960004a
Pichersky, E. and Raguso, R.A. (2018), Why do plants produce so many terpenoid compounds?. New Phytol., 220: 692-702. DOI:10.1111/nph.14178