The reason why the brain has receptors designed specifically for marijuana chemicals is that the brain actually produces cannabinoid substances similar to pot’s psychoactive ingredients. Cannabinoids are naturally made in the cortex, an area of the brain that guides movement, processes thoughts and emotions and interprets sensory information.
Anandamide is an important endogenous cannabinoid that functions as a neurotransmitter in the brain. Anandamide facilitates chemical messaging among neurons and the central nervous system nerve cells. Because marijuana’s primary psychoactive chemical THC is so comparable molecularly to anandamide and other cannabinoids, THC easily infiltrates and activates cannabinoid receptors.
Disruption of normal cannabinoid receptor activity causes the mental and physical effects of a pot “high.” In addition, smoking pot increases levels of dopamine and serotonin, two neurotransmitters implicated in sleep, mood and pleasure. The brains of daily marijuana smokers eventually develop a tolerance to excessive serotonin and dopamine levels, which forces the brain to reduce its natural release of these two chemicals. Consequently, having intense dreams after quitting weed could be due to a lack of serotonin and dopamine in the brain.