Final answer:
Cocaine acts as a stimulant by affecting neurotransmitter levels in the brain, leading to elevated dopamine and increased pleasure. However, this effect is short-lived, resulting in a crash and cravings for more cocaine.
Step-by-step explanation:
Cocaine acts as a stimulant by preventing nerve cells from taking up dopamine, another neurotransmitter, from the synapse. High levels of dopamine are therefore available to stimulate the pleasure centers of the brain. The enhancement of dopamine action is thought to be responsible for cocaine's "high" and its addictive properties. After the binge, dopamine is depleted in less than an hour. This leaves the user in a pleasureless state and (often) craving more cocaine.