The main neurotransmitter involved in addiction is dopamine, which is responsible for the triggering the pleasure/reward circuit as well as movement, attention, and memory. Additionally, dopamine plays a critical role in motivation. When an individual first experiments with a drug, the brain’s chemistry rebalances itself as the drug wears off and the substances are flushed from the body. Over time, however, the drug will create changes in cellular structure and function, and neurotransmission is affected.