impotence imˈpətəns [key], inhibited sexual excitement in a man during sexual activity that, despite an unaffected desire for sex, results in inability to attain or maintain a penile erection. Known medically as male erectile dysfunction, it affects younger and older men alike. Impotence can result from psychological factors (performance anxiety or fear of abandonment or unwanted pregnancy), sociocultural factors (negative sexual attitudes or religious beliefs), or physical causes. Impotence is distinguished from sterility (inability to produce sperm adequate for reproduction; see infertility).

Physical causes include low testosterone levels, diabetes, arteriosclerosis, prostate cancer surgery, and neurological diseases such as multiple sclerosis and Parkinson's disease. Many drugs, illicit (e.g., marijuana, heroin, and cocaine) and prescription (e.g., ulcer medicines such as cimetidine (Tagamet) and hypertension medicines such as beta-blockers and diuretics), have been associated with impotence in some men. Smoking and alcoholism also can inhibit sexual excitement. Often, more than one factor is involved. In general, anything that can affect the flow of blood to the penis can cause impotence.

Treatment depends on the underlying cause, and may involve education and counseling of the man and his partner. Treatments include self-injection of a vasodilating drug before intercourse, and implantation of rod-shaped devices into the penis that are inflated via an attached fluid reservoir. In 1998 the first prescription medication for the treatment of impotence, sildenafil (Viagra), was approved for sale in the United States. It acts by blocking an enzyme called phosphodiesterase 5 (PDE5), which can end an erection prematurely; vardenafil (Levitra) and tadalafil (Cialis) work similarly.

See also sex therapy.

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