The neuronal systems most likely to be affected in addiction involve reward, stress and self-control pathways, and the changes can persist long after the substance misuse or activity has stopped. Many neurotransmitters in the brain and central nervous system are implicated in dependence or addiction, and especially dopamine with the mesolimbic dopamine reward pathway implicated in all addictions.^4,7

Systems and related neurotransmitters/neuromodulators (which sometimes act hormonally) that change with repeated exposure to external drugs include:^8,9

·       - brain reward systems – dopamine, opioid peptides (endorphins, enkephalins and dynorphins), substance P, gamma aminobutyric acid (GABA), oestrogen;

·       - brain stress systems – corticotropin-releasing hormone (CRH), cortisol, noradrenaline/norepinephrine;

·       - brain anti-stress system – serotonin (5HT), dehydroepiandrosterone (DHEA), neuropeptide Y (NPY), endocannabinoids, galanin, oxytocin;

·       - glutamate associated with impulse control;

·      - brain-derived neurotrophic factor (BDNF) associated with neuroprotection.