Impotence means that a man's penis doesn't get hard enough to have sexual intercourse. The man cannot get or maintain an erection. The medical term is erectile dysfunction (ED).
ED is not the same as premature ejaculation.
The major causes of ED include:
Vascular (blood vessel) disease — Erections happen when blood collects in the shaft of the penis. Vascular disease can limit the amount of blood flowing to or staying in the penis. Both can result in problems with erections.
Vascular disease is the most common medical cause of impotence.
Nerve damage — Nerves must be working normally for a man to get and keep an erection. Nerves can be damaged by diabetes, multiple sclerosis, prostate surgery or damage to the spinal cord.
Psychological factors — Psychological issues such as depression, anxiety, guilt or fear can sometimes cause sexual problems. At one time, these factors were thought to be the major cause of impotence. Doctors now know that physical factors cause impotence in most men with the problem. However, embarrassment or "performance anxiety" can make a physical problem worse.
Medications — Many medications cause problems with sexual function. These include drugs for high blood pressure, depression, heart disease and prostate cancer.
Hormonal problems — Abnormal levels of certain hormones can interfere with erections and sex drive. Hormonal problems, such as a low testosterone level, are an uncommon cause of impotence.