Nearly all drugs of abuse increase dopamine neurotransmission. This slide shows the increase in dopamine (DA) measured directly in the brain of an animal in response to exposure to various drugs of abuse. All the drugs depicted in this slide have different mechanisms of action; however, all also increase activity in the reward pathway by increasing dopamine neurotransmission. Because drugs activate these brain regions?usually more effectively and for longer periods of time than natural rewards?they have an inherent risk of being abused.