Those neurochemicals that are commonly associated with this type of reward/pleasure system in the brain are dopamine, serotonin, glutamine. The same set of neurochemicals are released with the consumption of alcohol and drugs that create a sense of pleasure or a change in mood. This is what’s known as a reward, or what is referred to as “the payoff.”
Over time, the continued stimulation of the pleasure center chemicals causes changes to the reward, motivation, and memory centers. Once the body and brain becomes dependent on the “payoffs” of these chemicals, it becomes necessary to abuse the substances in order to just feel normal and to function properly.
Without the substances, the person experiences cravings and an intense desire for the substance and will use them despite negative, or even dangerous consequences.