"Amphetamines enhance release of catecholamines, increasing intrasynaptic levels of norepinephrine, dopamine, and serotonin. The resulting marked ?- and ?-receptor stimulation and general CNS excitation account for the “desired” effects of increased alertness, euphoria, and anorexia, as well as the adverse effects of delirium, hypertension, hyperthermia, and seizures. Effects of amphetamines are similar, varying in intensity and duration of psychoactive effects; MDMA and its relatives have more mood-enhancing properties, perhaps related to a greater effect on serotonin. Amphetamines can be taken orally as pills or capsules, nasally by inhaling or smoking, or by injection.
"Chronic effects: Repeated use of amphetamines induces dependence. Tolerance develops slowly, but amounts several 100-fold greater than the amount originally used may eventually be ingested or injected. Tolerance to various effects develops unequally. Tachycardia and increased alertness diminish, but hallucinations and delusions may occur.
"Amphetamines typically cause erectile dysfunction in men but enhance sexual desire. Use is associated with unsafe sex practices, and users are at increased risk of sexually transmitted infections, including HIV infection. Amphetamine abusers are prone to injury because the drug produces excitation and grandiosity followed by excess fatigue and sleepiness."
"Amphetamine," The Merck Manual for Health Care Professionals, Special Subjects: Drug Use and Dependence: Amphetamines, Merck & Co. Inc., Revised: July 2008.