Amphetamine and its derivatives, prototype stimulants, are available in immediate and long-acting formulations. Amphetamines act by multiple mechanisms including reuptake inhibition, displacement of transmitters from vesicles, reversal of uptake transporters and reversible MAO inhibition. Thus amphetamines actively increases the release of these neurotransmitters into the synaptic cleft. In the short term, methylphenidate, a benzylpiperidine and phenethylamine derivative stimulant medication, is well tolerated. However, long-term studies have not been conducted in adults and concerns about increases in blood pressure have not been established. Methylphenidate increases concentrations of dopamine and norepinephrine in the synaptic cleft, promoting increased neurotransmission. It acts to block the dopamine and norepinephrine reuptake transporters, thus slowing the removal at which these neurotransmitters are cleared from the synapses. Dextroamphetamine is a short-acting amphetamine.