Addiction is present when endogenous forms of neurotransmitters are downregulated in response to sustained external supply. As such, the receptor regulation sys

Addiction is present when endogenous forms of neurotransmitters are downregulated in response to sustained external supply. As such, the receptor regulation systems do not see a 'need' to self regulate and upon cessation of said 'sustained external supply' psychosomatic factors drive motivation (VTA theory). Having said that, there are chemically mediated addictions and psychosomatic addictions (the two are not mutually exclusive).