Erectile dysfunction is characterized by the regular or repeated inability to obtain or maintain an erection. There are several ways that erectile dysfunction is analyzed:
- Obtaining full erections at some times, such as when asleep (when the mind and psychological issues, if any, are less present), tends to suggest the physical structures are functionally working. However, the opposite case, a "lack" of nocturnal erections, does not imply the opposite, since a significant proportion of sexually functional men do not routinely get nocturnal erections or wet dreams.
- Obtaining erections which are either not rigid or full ("lazy erection"), or are lost more rapidly than would be expected (often before or during penetration), can be a sign of a failure of the mechanism which keeps blood held in the penis, and may signify an underlying clinical condition, often cardiovascular in origin.
- Other factors leading to erectile dysfunction are diabetes mellitus (causing neuropathy) or hypogonadism (decreased testosterone levels due to disease affecting the testicles or the pituitary gland).
A few causes of impotence may be androgenic (medically caused). Various anti hypertensives (medications intended to control high blood pressure) and some drugs that modify central nervous system response may inhibit erection by denying blood supply or by altering nerve activity.
Surgical intervention for a number of different conditions may remove anatomical structures necessary to erection, damage nerves, or impair blood supply. Complete removal of the prostate gland or external beam radiotherapy of the gland are common causes of impotence, both are treatments for prostate cancer. Some studies have shown that male circumcision may result in an increased risk of impotence, while others have found no such effect, and another found the opposite.