Amphetamines increase the activity of the monoamine neurotransmitters:serotonin, epinephrine, norepinephrine, and dopamine. The drugs stimulate the release of these neurotransmitters, which leads to elevated levels of the neurotransmitters in the synapses (the gaps between neurons.) In addition, amphetamines inhibit monoamine oxidase, the enzyme responsible for the destruction of serotonin, epinephrine, norepinephrine, and dopamine, further increasing their levels in the brain. With an excess of these chemicals in the brain, the individual at first feels extremely energetic and content. Over time, however, normal functioning becomes impossible.
The most prominent monoamine neurotransmitter involved in the effects of the amphetamines is dopamine. Dopamine causes the desirable effects of the drugs, as well as some of the most disturbing psychological effects of the drugs, such as the stereotypic behaviors and psychosis.