What are terpenes? Meaning, examples and research

Terpenes are the aromatic compounds that give plants such as pine, lavender, citrus and hemp their smell. Chemically, they are hydrocarbons built from five-carbon isoprene units. Cannabis makes them in the resin glands of its flowers, alongside cannabinoids such as CBD and THC. How much terpenes add to the effects of cannabis is still debated in research.

What does terpenes mean?

The word describes a large family of natural compounds that plants make from small building blocks called isoprene units. Each unit has five carbon atoms. Two units joined together make a monoterpene, such as limonene or myrcene. Three units make a sesquiterpene, such as caryophyllene or humulene. When a terpene carries oxygen, for example as an alcohol group, chemists call it a terpenoid. Linalool and borneol are terpenoids, although most people simply call them terpenes. Citrus-scented valencene is another sesquiterpene.

So a short definition of terpenes is: the volatile, fragrant hydrocarbons that make up most of a plant's essential oil. They are the reason a lemon peel, a pine forest and a hemp field each smell the way they do.

Where are terpenes found?

Almost every plant makes terpenes. Conifers, citrus fruit, herbs such as rosemary and basil, and flowers such as lavender are rich in them. In plants, terpenes help keep pests away and attract pollinators. Some also act as building blocks for pigments and plant hormones. Pine and spruce resin, for example, contain delta-3 carene.

In cannabis and hemp, terpenes are made in the glandular trichomes, the tiny resin glands that cover the female flowers. The same glands make the cannabinoids (Sommano et al., 2020). That is why the flowers smell much stronger than the stem or the seeds.

Which terpenes are found in cannabis?

A 2020 review counted more than 200 volatile compounds reported from different cannabis plants. Of these, 58 monoterpenes and 38 sesquiterpenes had been characterised (Sommano et al., 2020). A handful of them make up most of the aroma in most plants.

Smaller amounts of others, such as ocimene, camphene and borneol, can still shape how a particular plant smells.

Why do cannabis varieties smell different?

Every cannabis plant has its own mix of terpenes, and the mix depends on genetics, growing conditions, harvest time and storage. That is why two varieties with similar CBD or THC content can smell completely different.

Researchers have found that strain names are a poor guide to what is in the plant. A review in Plant Science notes concerns about the lack of consistency in the terpene and cannabinoid make-up of different "strains" (Booth and Bohlmann, 2019). An analysis of more than 800 commercial varieties linked the flavours users reported to the terpenes in those plants. The authors note that terpene content is strongly inherited, so flavour could help characterise a variety (de la Fuente et al., 2020). The only reliable way to know a plant's terpene profile is a laboratory analysis.

Prefer watching over reading? This video covers the basics:

Do terpenes affect how cannabinoids work?

This question sits behind the idea of the entourage effect: the theory that the many compounds in cannabis act differently together than on their own. Terpenes are often named as part of it, but the evidence points both ways.

• For: in a 2021 study in mice and cells, the terpenes humulene, geraniol, linalool and beta-pinene produced some cannabinoid-like behaviours and added to the activity of a synthetic cannabinoid. The authors say this gives "conceptual support" to the entourage hypothesis (LaVigne et al., 2021).
• Against: a 2020 study tested myrcene, alpha- and beta-pinene, beta-caryophyllene and limonene at the CB1 and CB2 receptors. Apart from a possible weak interaction of beta-caryophyllene with CB2, none changed how THC, CBD or the body's own endocannabinoid acted there (Finlay et al., 2020).

Both are laboratory or animal studies. They do not show what terpenes do in people, and the question remains open.

How are terpenes studied?

Most terpene research looks at plants, aroma chemistry and laboratory models. One example is a 2023 review of terpenes from medicinal plants in Asia and the Pacific that showed antibacterial or antifungal activity in laboratory tests; it identified about 300 such compounds (Wiart et al., 2023). Results like these describe what a pure compound does in a test tube. They say nothing about a hemp product or about effects in the body.

Terpenes are also sensitive to heat, light and air. They evaporate and break down over time, which is one reason the aroma of dried plant material fades.

What is the difference between terpenes and cannabinoids?

Both are made in the same resin glands, but they are different kinds of molecule. Terpenes occur in almost every plant and are responsible mainly for smell and taste. Cannabinoids such as CBD and THC are largely specific to cannabis and act on the body's endocannabinoid system. For an overview of that group, see our guide to what cannabinoids are.

Our CBD oils are made from Swiss hemp extract that keeps its natural terpenes.