In small to moderate doses, amphetamine causes elevations in heart rate, body temperature, respiration, and blood pressure as well as extra energy, and appetite suppression. Long-term use can have a number of side effects, including depression, lethargy, sleep deprivation, heart and blood vessel toxicity, and malnutrition.
Prolonged, heavy or chronic use can lead to a (usually temporary) schizophrenia-like psychosis, known as amphetamine psychosis, characterised by delusions, thought disorders and hallucinations.