Amphetamines are a class of pharmaceuticals that result in an increase in metabolic functions, resulting in a higher heart rate and respiration rate.
Amphetamines were once commonly used as diet pills (as one of their side effects is the reduction of hunger) and aids for drowsiness (as they increase alertness). However, they are habit forming and stopping use of the drug results in severe symptoms of withdrawal. In addition, severe insomnia is a common side effect of even moderate use. As such, they are rarely used for such purposes by responsible physicians, although they are often abused by patients.