Erectile dysfunction (ED) or impotence is sexual dysfunction characterized by the inability to
develop or maintain an erection of the penis during sexual activity.  A penile erection is
the hydraulic effect of blood entering and being retained in sponge-like bodies within the penis. The
process is most often initiated as a result of sexual arousal, when signals are transmitted from
the brain tonerves in the penis. The most important organic causes are cardiovascular
disease and diabetes, neurological problems (for example, trauma
from prostatectomy surgery), hormonal insufficiencies (hypogonadism) and drug side effects.
Psychological impotence is where erection or penetration fails due to thoughts or feelings
(psychological reasons) rather than physical impossibility; this is somewhat less frequent but can
often be helped. Notably in psychological impotence, there is a strongresponse to placebo
treatment. Erectile dysfunction can have severe psychological consequences as it can be tied to
relationship difficulties and masculine self-image.