Cocaine addiction and misuse can be caused by how it affects the dopamine neurotransmitter system in the brain. Dopamine is associated with ‘happy’ emotions, the regulation of movement, and the processing of the reward center of the brain. While people using cocaine may feel these highs for a short time, once the drug begins to leave the system, they may experience adverse reactions, including irritability, anxiety, disorientation, and restlessness. This quickly leads to agitation that is again then subsided by another dose of cocaine.