Along with more than 100 cannabinoids, the cannabis plant contains more than 20 different terpenes. While the cannabinoids are unique to cannabis, the terpenes are found in many plant species. Many terpenes have medicinal properties in their own right and are now being found to interact with cannabinoids to produce a range of effects.
What Are Terpenes?
Terpenes belong to a class of compounds known as aromatic hydrocarbons, and they are made up of chains of linked isoprene units. Isoprene is an abundant naturally occurring molecule with the chemical formula C₅H₈, and terpenes are formed by two or more linked isoprene units. Thus, monoterpenes (C₁₀H₁₆) are formed of two isoprene units, diterpenes (C₂₀H₃₂) from four, triterpenes (C₃₀H₄₈) from six, and so on.
Terpenes are a major component of many plant resins, cannabis being no exception. Most terpenes are strong smelling and often serve the purpose of attracting pollinators or repelling predators. Furthermore, it is thought that certain tree species release terpenes, which react with atmospheric compounds to produce aerosols, which in turn encourage water vapor to form clouds. During hot weather, these trees release higher levels of terpenes, doubling cloud cover and providing a strong cooling effect.
Terpenes Found in Cannabis
Some notable terpenes contained within the cannabis plant include d-limonene, myrcene, pinene, camphene, sabinene (all monoterpenes), squalene (a triterpene), and α-humulene and caryophyllene (both sesquiterpenes, which are made up of three isoprene units and have the chemical formula C₁₅H₂₄). According to one source, cannabis contains 58 monoterpenes and 38 sesquiterpenes. Many related compounds known as terpenoids are also contained within cannabis (such as linalool and geraniol, and even cannabinoids themselves); however, for purposes of simplicity, we will focus only on the true terpenes.
Medical Benefits of Terpenes
Terpenes have been found to have a range of medicinal benefits in their own right. For example, limonene has been shown to have anticarcinogenic properties (Elson et al. 1997); myrcene, limonene and citral have demonstrated sedative and motor relaxant effects (Vale et al. 2002); and myrcene has been shown to have analgesic effects on peripheral pain (Lorenzetti et al. 1991).
A number of studies also observed potential medical properties in the essential oil of various plant species. Essential oils, which are derived from plants via steam distillation or solvent extraction, typically contain terpenes in higher concentrations than any other constituent. For example, a 2008 study (Gilani et al) investigated the essential oil of Nepeta cataria (catnip), which contains the terpenes pinene and α-humulene, and found it to have bronchodilatory and antispasmodic effects.
Another study (Farag et al. 1989) demonstrated that the essential oils of six herbs and spices (sage, rosemary, caraway, cumin, clove and thyme) known to be high in various terpenes including pinene, camphene and limonene demonstrated antimicrobial activity against various gram-positive bacteria. Sage and cumin oils exhibited particularly strong antimicrobial activity.
Interactions with the Endocannabinoid System
Many terpenes were also found to interact synergistically with cannabinoids by directly or indirectly acting on the cannabinoid receptors. Most notably, recent reports have highlighted the likelihood that the monoterpene myrcene interacts with THC to produce the characteristic “couch-lock” effect associated with “indica” varieties.
Likewise, earlier research demonstrated that the sesquiterpene caryophyllene (the oxide of which is the compound drug-sniffing dogs are trained to detect) acts as a selective CB₂-receptor agonist and has anti-inflammatory properties via this mechanism.
Dr Ethan Russo (former senior medical advisor at U.K. cannabinoid research company GW Pharmaceuticals) released an extensive review of the existing medical literature investigating the synergy between cannabinoids, terpenes and terpenoids. On the basis of his research and others, the concept of the “entourage effect”—the synergistic biological effects of the various compounds in cannabis—was developed.
The entourage effect is the focus of intense research, and it is clear that we are only beginning to understand the complexities of the thousands of potential interactions between these many and varied compounds.