Amphetamine (alpha-methyl-phenethylamine), also known as speed, is a synthetic stimulant used to suppress the appetite, control weight, and treat disorders including narcolepsy and Attention-deficit hyperactivity disorder. It is also used recreationally and for performance enhancement (these uses are illegal in most countries).
Due to the widespread use of amphetamines as a treatment for ADD/ADHD in the USA, Canada, and other countries, they frequently find their way onto the street and are one of the most frequently-abused drugs in high schools and colleges.
Effects of use
Amphetamines release stores of norepinephrine and dopamine from nerve endings by converting the respective molecular transporters into open channels. Amphetamine also releases stores of serotonin from synaptic vesicles. Like methylphenidate (Ritalin), amphetamines also prevent the monoamine transporters for dopamine and norepinephrine from recycling them (called reuptake inhibition), which leads to increased amounts of dopamine and norepinephrine in synaptic clefts.
These combined effects rapidly increase the concentrations of the respective neurotransmitters in the synaptic cleft, which promotes nerve impulse transmission in neurons that have those receptors.
Short-term physiological effects include decreased appetite, increased stamina and physical energy, increased sexual drive/response, involuntary bodily movements, increased perspiration, hyperactivity, jitteriness, nausea, itchy, blotchy or greasy skin, increased heart rate, irregular heart rate, increased blood pressure, and headaches. Fatigue can often follow the dose's period of effectiveness. Overdose can be treated with chlorpromazine. 
Long-term abuse or overdose effects can include tremor, restlessness, changed sleep patterns, poor skin condition, hyperreflexia, tachypnea, gastrointestinal narrowing, and weakened immune system. Fatigue and depression can follow the excitement stage. Erectile dysfunction, heart problems, stroke, and liver, kidney and lung damage can result from prolonged use. When snorted, amphetamine can lead to a deterioration of the lining of the nostrils.
Short-term psychological effects can include alertness, euphoria, increased concentration, rapid talking, increased confidence, increased social responsiveness, nystagmus (eye wiggles), hallucinations, and loss of REM sleep the night after use.
Long-term psychological effects can include insomnia, mental states resembling schizophrenia, aggressiveness (not associated with schizophrenia), addiction or dependence with accompanying withdrawal symptoms, irritability, confusion, and panic. Chronic and/or extensively-continuous use can lead to amphetamine psychosis, which causes delusions and paranoia, but this is uncommon when taken as prescribed. Amphetamine is highly-psychologically addictive, and, with chronic use, tolerance develops very quickly. Withdrawal is, although not physiologically threatening, an unpleasant experience (including paranoia, depression, difficult breathing, dysphoria, gastric fluctuations and/or pain, and lethargia). This commonly leads chronic users to re-dose amphetamine frequently, explaining tolerance and increasing the possibility of addiction.