Because the penis needs adequate blood flow to become erect, blood vessel disorders such as atherosclerosis can cause impotence. Impotence can also result from a blood clot or from vascular surgery that impairs arterial blood flow to the penis. In 75 percent of impotent men who have normal neurologic and hormonal function, the blood flows into the penis properly, but it flows out too rapidly. Damage to the nerves leading to and from the penis also can produce impotence. Such damage may result from many causes, including injury, diabetes mellitus, multiple sclerosis, stroke, and drugs.
Alcoholism causes a similar peripheral neuropathy.
Lower spinal disease and rectal or prostate surgery can also damage the nerves of the penis. Drugs are involved in an estimated 25 percent of impotence cases, especially in elderly men, who tend to take more drugs. The drugs that most commonly cause impotence include all antihypertensives, antipsychotics, antidepressants, some sedatives, cimetidine, and lithium. Alcohol also can cause impotence. Occasionally, impotence results from hormonal disturbances.