Our understanding of how cannabis works on the brain is still less than complete. The strength or purity of the drug is measured as a percentage according to the amount of THC it contains, calculated against weight.
Cannabis contains over 400 chemicals; some 60 plus of these are chemically unique and are known as cannabinoids. Delta-9 tetrahydrocannabinol (THC) is generally regarded as the alkaloid primarily responsible for the plant’s psychoactive effects, though there is on-going research into the pharmacological action of the spread of cannabinoids. Medical users are particularly attracted to Cannabidiol (CBD) for its sedative/anxiolytic properties. and research has been carried out on these effects. CBD is also believed by some users and researchers to modify the effect of THC.
Cannabis works by binding to specific cannabinoid receptors (CB1 and CB2) within the cerebral cortex, hippocampus, hypothalamus, cerebellum, basal ganglia, brain stem, spinal cord and amygdala, a very diverse set of locations associated with diverse functions, providing the neurological substrate of the great variety of experiential effects associated with cannabis ingestion. As in the case of opium, the discovery of cannabinoid receptors in the human brain and nervous system for chemicals derived from plants led to a search for the endogenous alkaloid to which these receptors would naturally bind; an endogenous cannabinoid was duly discovered in 1988 and named anandamine, after ananda, the Sanskrit word for bliss.
Cannabis as a pain reliever
Cannabinoid receptors are present in pain processing pathways (part of the mechanisms involved in instigating and relieving pain). When cannabis is administered (orally or otherwise), the active metabolite THC acts on its relevant receptors and stimulates the pathways that are closely related to inhibiting pain. As a homeostatic mechanism, as soon as pain signals are sent to the brain, inhibitory pain signals respond back to try and relieve it naturally. With mild analgesics such as cannabinoids, the signals going to the brain instigating pain are reduced AND the inhibitory signals going back are enhanced.