Cocaine dramatically increases dopamine levels in the brain's reward centers by blocking its normal reuptake.

Under normal conditions, the neurotransmitter dopamine is released to signal reward and is quickly recycled back into the transmitting cell. Cocaine binds to these recycling transporters, trapping dopamine in the synaptic gap. This causes a massive, continuous build-up of the chemical, overstimulating the receiving neurons. This overstimulation is what produces the intense, immediate feelings of euphoria and alertness.