Erectile dysfunction (ED) can be a total inability to achieve erection for sexual intercourse, an inconsistent ability to do so, or a tendency to sustain only brief erections. It is estimated that between 15 million and 30 million American men experience erectile dysfunction. However, the condition's broad variations make it difficult to define it or estimate its incidence. In older men, the cause is usually something physical like disease, injury, or side effects of drugs; but any disorder that causes injury to the nerves or impairs blood flow in the penis can potentially cause erectile dysfunction. The condition is treatable at any age through psychotherapy; drug therapy; vacuum devices; surgery; or lifestyle changes like losing weight, quitting smoking, and exercising more.