Terpenes
It is being observed that cannabinoids are not the only active substances in the Cannabis plant. Certain studies showed that there were differences between the effects produced by pure cannabinoids and the ones caused by the plant, although cannabinoids are administered in equal doses in both cases. These observations point to the existence of other active substances in the Cannabis plant, which have an intrinsic pharmacological action and/or can modify the pharmacological action of cannabinoids. Two groups of active substances have been identified presently; terpenes and flavonoids, both of which appear in sufficient concentrations to have pharmacological activity. From a scientific perspective, neither which kind of specific compounds are capable of producing synergy with cannabinoids, nor how they are formed, have been proven. Both terpenes and flavonoids are under the increasing attention of the scientific and medical community due to their proven pharmacological actions. In the following paragraphs, we will try to show the current state of the studies about the biological and synergistic activity between these active substances and the cannabinoids.
Terpenes
Terpenes are volatile organic compounds formed by the union of hydrocarbon of 5 carbon atoms, known as isoprene. The smallest and most volatile compounds are monoterpenes, which are biosynthesised by the union of two isoprene molecules. The biggest and least volatile are biosynthesised by the union of three or more isoprene molecules. The sesquiterpenes are next in the chain, which are formed by the union of three isoprene molecules. Terpenes are secondary metabolites, which provide the plant with its organoleptic characteristics (aroma and flavour) and that constitutes most of the essential oil produced by aromatic plants.
Terpenes and cannabinoids share their biosynthetic pathways and, in fact, cannabinoids are terpeno-fenolic compounds. In the Cannabis plant, terpenes also share the biosynthesis and accumulation spaces. Thus, both types of compounds are biosynthesised in the glandular trichomes of leaves and flowers and are accumulated in large proportions in the exuded resin. In any case, it seems that certain non-capitular glandular trichomes, which are more abundant in leaves surface, are specialised in synthesising terpenes. It has been shown that the ratio between monoterpenes and sesquiterpenes in leaves and flowers is rather different. This is due to the dominance of sessile trichomes in leaves, which are more specialised in synthesising terpenes, while capitate trichomes are more abundant in flowers and are specialised in the synthesis of monoterpenes and cannabinoids. The proportion of terpenes in the plant is normally less than 1%, potentially achieving up to 10% of the resin composition.
Terpenes have different functions in plants. The two main ones are the protection against insects and herbivorous animals, as well as protection against high temperatures. Plants react by producing terpenes in the areas affected through the action of insects and herbivorous animals, which act as bitter compounds that repel them or even as pesticides in some cases. Monoterpenes, which are more volatile, dominate in inflorescences to repel insects. Sesquiterpenes, which are more bitter, are more abundant on leaves acting against herbivorous animals. Some terpenes can act as a decoy in some plants, attracting either pollinating insects or predatory ones that feed on herbivorous insects, which are beneficial for the plant. As plants sense a temperature rise, they begin synthesising more terpenes and under high temperatures during night or day, more terpenes are released. Terpenes evaporate at high temperatures, producing airflows that cool the plant and lessen transpiration, preventing the plant from drainage. In the Cannabis plant, terpenes are exuded in the resin and confer it with the sticky and viscous quality that will get some insects trapped and immobilised, thus, acting as a protection against insects and high temperatures. Hence, it is easy to observe that Cannabis plants smell stronger during the first morning hours than during the warmest part of the day as a large amount of terpenes evaporate. This is the reason why it is recommended harvesting the mature plants during the first morning hours, in order to get the maximum production of essential oil.
Cannabis essential oil is mainly formed by a high proportion of monoterpenes and a variable proportion of sesquiterpene. Such proportions, together with the extraction performance, will be mainly affected by the degree of drying that Cannabis achieves when processed for the extraction of the essential oil. In fact, the extraction performance of the essential oil by steam distillation of the fresh plant is lower than 1%, with a composition of 80-90% in monoterpenes and 10-20% in sesquiterpenes. However, it will be around 0.1% in the dried plant and its composition will be lower in monoterpenes, where it can reach 50% in sesquiterpenes, due to the fact that monoterpenes are very volatile and evaporate quickly during the plant drying process. Usually, the essential oil obtained from industrial hemp, which contains many leaves and it is normally processed dried, is chiefly formed by sesquiterpenes. Some sesquiterpenes remain in the plant even after a 15 minute decarboxilation treatment at 120oC. This is the case for cariofileno, which has a moist soil aroma characteristic of baked or cooked Cannabis. Likewise, the evaporation of monoterpenes during the drying process is responsible for the transformation of the aroma from the fresh plant to a well-dried one, although the change in taste comes from the degradation of chlorophylls. Thus, fresh plants have minty, citric, fruity, etc. aromas that soften when dried.
Nevertheless, terpenes are not just responsible of the aroma, but they also have an important biological and therapeutic activity. It has been scientifically shown that the essential oils of plants have therapeutic properties and are the pharmacological base of aromatherapy. These oils and pure terpenes can also be used as flavourings in the food industry, as they are non-toxic compounds. The therapeutic properties will specifically depend on the terpene in question.
The most abundant terpenes in the Cannabis plant that form most of its essential oil are the monoterpenes myrcene, pinene, limonene, linalool, eucalyptol and sesquiterpene caryophyllene. The variation in the ratio between these terpenes is what produces the wide range of aromas that can be found in the Cannabis plant. It has been recently discovered that they can also take part in the varied pharmacologic effects caused by Cannabis, as well as generate synergy with cannabinoids.