Cannabigerol (CBG) is a phytocannabinoid—i.e. one that occurs naturally in plants, as opposed to produced within the body (known as endocannabinoids) or synthesised. CBG is found in higher concentrations in hemp strains, and is usually present in relatively low levels in drug cannabis varieties.
CBG & the endocannabinoid system
Believed to be non-psychoactive, it is believed that CBG acts as a mild CB1-receptor antagonist, a receptor ligand that binds to the receptor and prevents agonists such as THC from exerting an effect.
As well as this, CBG has been shown to exert an effect on the 5HT1?-receptor, which assists in the regulation of serotonin release, and the adrenoceptor, which controls expression of adrenaline and noradrenaline throughout the central nervous system.
There is evidence to suggest that CBG exerts influence on the CB2-receptor, but it not clear whether this effect is agonistic or antagonistic in nature.
Chemical properties of CBG
As with all cannabinoids, CBG is a hydrophobic lipid comprised of a 21-carbon chain attached to an aromatic hydrocarbon ring. The chemical formula of CBG is C21H32O2; that of THC is C21H30O2, as is that of CBC (cannabichromene) and CBD. CBC and CBD are both isomers of THC, meaning that they share the same molecular formula but have different structures.
CBG is closely related to several other cannabinoids including cannabigerolic acid (C22H31O4), also known as CBGA, which is an important precursor for THC. CBG itself degrades to CBD and CBC, and it is also possible for CBG to degrade directly to THC, through the actions of the acid synthase enzyme unique to each cannabinoid (i.e. THC- CBD- and CBC-acid synthase). This process is relatively new to the scientific community, as it was previously believed that THC was an end-product of CBD degradation.
The CBG group of cannabinoids
The cannabigerol-type cannabinoid group contains seven related molecules including CBG itself. As well as CBG and CBGA, the CBG group contains cannabigerovarin (CBGV), cannabinerolic acid A (CBNA), cannabigerovarinic acid A (CBNVA), and the monomethyl esters of CBG and CBGA, CBGM and CBGAM respectively.
This group of cannabinoids is relatively understudied; however, it is believed that CBNA is also a precursor to THC in certain conditions. The molecular pathways through which THC is biosynthesised are still being discovered, and successful laboratory synthesis often occurs in different ways that those occurring in vivo. This partly explains why it was believed that THC is naturally synthesised from CBD, as until recently it was the only tested method for laboratory synthesis.
The CBG-dominant chemotype
In nature, the tendency for populations to tend towards a CBG-dominant chemotype (chemical phenotype) has been noted in certain regions, mostly in the high latitudes where hemp strains traditionally dominate. In ‘normal’ cannabis plants, CBG makes up no more than 10% of the cannabinoid profile; in CBG-dominant plants, the figure may be as high as 94%. In such populations, there is often a corresponding, remarkably low expression of THC, as little as 0.001% in some specimens.
It is believed that a recessive allele type at a single gene locus is responsible for this phenomenon. The locus in question, known simply as B, is thought to control the synthesis of THC or CBD from CBG. The CBG-dominant type has the allele B0,which encodes for a defective acid synthase, inactivating the process of synthesis and leading to unusually high CBG levels with correspondingly low THC.
The discovery of this phenomenon has led to improved understanding of the genetic mechanisms through which varieties that are dominant in just one cannabinoid can arise. Such varieties are potentially of great medicinal importance as they allow for easier extraction and study of the dominant cannabinoid.
Medicinal properties of CBG
Although CBG has not been extensively studied for its medical properties, several studies have been conducted. A 2009 study on glaucoma in cats concluded that both THC and CBG reduce intraocular pressure and increase aqueous outflow through the intricate mesh of drainage channels in the tissue surrounding the eye.
CBG has also been found to have an anti-nausea and anti-emetic (anti-vomiting) effect on rats, although this research has not been replicated in humans. Further, CBG has demonstrated an anti-inflammatory effect on inflammatory bowel disease and colitis in mice. As well as this, CBG has also been shown to reduce pain, ease symptoms of psoriasis, act as an antibacterial agent and even slow the proliferation of tumour cells.