CBD terpenes: 200 molecules, under 1% of the flower

A terpene is an organic compound assembled from isoprene, a small molecule of five carbon atoms. Two isoprene units make a monoterpene (10 carbons), three a sesquiterpene (15) and four a diterpene (20). A molecule that also carries an oxygen atom, linalool for instance, is called a terpenoid, though everyday usage mixes the two words.

Most monoterpenes are volatile. They evaporate at room temperature and reach the nose, which is how we perceive them. Heavier sesquiterpenes evaporate more slowly.

Plants produce a vast number of them. In a review published in 2011 in the British Journal of Pharmacology, pharmacologist Ethan Russo puts the number of fully characterised terpenoids at 15,000 to 20,000. More than 200 of them have been reported in cannabis. Their yield in the plant is low, under 1% in most analyses, though they can reach 10% of trichome content.

Trichomes are the tiny glands covering female flowers. According to a study published in 2020 in Scientific Reports, cannabinoids and terpenoids are produced and stored there, in the secretory cells. An extraction that preserves one group therefore often preserves the other. These glands are described in our article on trichomes, and the other family in the one on cannabinoids.

The terpene profile depends on the strain, the growing conditions, drying and storage. Even so, a handful of terpenes appear in most analyses.

The name of a strain says nothing certain about its dominant terpene. Limonene may not lead in a flower called "Lemon", and only a terpene assay, when the lab runs one, can tell. Our guide to the certificate of analysis shows where those lines appear. The CBD flower product pages describe the aroma profile of each product.

Among the common hemp terpenes, β-caryophyllene is a special case. A study published in 2008 in PNAS showed that it binds selectively to the CB2 receptor, with a binding constant of 155 nanomolar, and does not bind to the CB1 receptor. The THC high comes from CB1, in the brain, so β-caryophyllene does not get you high.

The authors note that it is widespread in spices and estimate possible dietary intake at 10 to 200 mg a day. Cannabis essential oil can contain up to 35% of it. Their inflammation experiments used mice and tell us nothing about the effect of CBD flower in humans. This work is reviewed in our article on β-caryophyllene and the CB2 receptor.

The "entourage effect" is the idea that hemp compounds act differently together than each would alone. Russo formalised it in his 2011 review and proposed that terpenes modulate the action of cannabinoids. His benchmark was that a terpene present above 0.05% would be of pharmacological interest.

Researchers have tested the hypothesis at the receptor level. In 2020 a team published results in Frontiers in Pharmacology on five terpenes: myrcene, α-pinene, β-pinene, β-caryophyllene and limonene. None of them, alone or in mixtures, changed CB1 or CB2 receptor signalling, even when combined with THC, CBD or an endocannabinoid. Any entourage effect would therefore have to work through some route other than direct action on these receptors.

No European authority has approved any health claim linked to terpenes or to the entourage effect. A seller who claims that terpenes "strengthen" CBD goes further than the data allow. The human trials are covered in our review of the entourage effect.

Volatility gives terpenes their scent and also makes them fragile. A study published in 2024 in the journal Plants compared four drying methods on two strains. Monoterpenes proved more sensitive to drying than sesquiterpenes. d-Limonene fell by up to 58% in one strain and held steady in the other. Depending on the case, β-myrcene dropped by 3 to 30%, and one method raised it by 15%. The relative concentration of β-caryophyllene went up, by as much as 50%.

Losses continue in storage. A study published in 2020 in Frontiers in Plant Science found that terpenoids in stored flowers had lost more than 50% within four months at every temperature tested. Cannabinoids lost 26% on average over a year. When a flower barely smells, most of its terpenes are gone. The practical rules are set out in our guides to drying and curing and to storing flower.

A CBD isolate is purified cannabidiol, free of terpenes and other cannabinoids and almost odourless. A full-spectrum extract retains hemp's terpenes and other cannabinoids, along with traces of THC below the legal limit of 0.30%. A broad-spectrum extract strips out the THC and retains everything else.

Some manufacturers add isolated terpenes, at times sourced from other plants, to rebuild an aroma, and an honest product states this on its label. Our comparison of full spectrum and isolate can help you choose for your own use.

According to Russo, these terpenes are common food flavourings with a known safety profile. On the skin, the situation differs. EU cosmetics law lists limonene and linalool among the fragrance allergens that must be named on the label above 0.001% in a leave-on product and 0.01% in a rinse-off product. You may therefore find them in the ingredient list of a full-spectrum CBD cream. Our article on fragrance allergens in CBD cosmetics explains how to spot them.