The business of the nervous system is to transmit information from one cell to another. Although this happens in different locations and with different neurotransmitters, the basic process is common to all cell-to-cell transmission. First, neurotransmitter molecules must be synthesized. Then, they must be packaged in synaptic vesicles. At the appropriate time, they must exit the cell by exocytosis, cross the synaptic cleft and bind and activate receptors on the post-synaptic neuron. The neurotransmitter molecules must then be either degraded or taken back into the presynaptic neuron, a process known as reuptake. Psychoactive drugs exert their effects by interfering with one or more of these steps.

Some of these drugs, known as stimulants, increase synaptic activity. Amphetamines, for example, increase the release from presynaptic cells of the group of neurotransmitters known as catecholamines. These include epinephrine, norepinephrine, and...