Erectile Dysfunction and its Causes

An estimated 20 million American men suffer from some degree of erectile dysfunction (ED). Commonly called impotence, ED is the persistent inability to achieve and sustain an erection sufficient for sexual intercourse. ED does not affect libido or the ability to have an orgasm. (Ejaculation may also be possible). The incidence of ED rises sharply with age, and as many as one-third of men over 60 have the condition.

What causes ED?

An erection occurs when arteries in the penis widen and veins narrow to prevent blood outflow. As a result, blood rushes into the penis, becomes trapped and produces an erection. Impotence occurs when something interferes with this process.

Up to 75 percent of all cases of ED can be traced to underlying medical conditions. The main causes are nerve disorders, vascular problems and medications.

 Nerve disorders.  The nerves are signal carriers that relay information from the brain to penile tissues, causing the blood vessels to open and blood to rush into the penis. If there is a problem with these nerves, the messages aren't transmitted correctly and the ability to have or maintain an erection can become impaired.

The major cause of penile nerve problems is diabetes mellitus, which often damages nerves and prevents nerve impulses from reaching the penis. In some cases, diabetes delivers a double threat: in addition to damaging nerves, it also encourages atherosclerosis in the arteries, which causes blockages that interrupt blood flow to the penis.

Other nerve-related disorders include multiple sclerosis and Parkinson's disease. Nerve disruptions can also result from back surgery or disc herniation in the lower back; surgery to remove cancer from the prostate, lower rectum or colon; and radiation therapy to the pelvic area.

Vascular problems. The major vascular cause of erectile difficulties typically originates from problems with the two, deep cavernosal arteries, or the larger arteries that feed blood to these cavernosal vessels. The culprit is atherosclerotic narrowing, which diminishes blood flow through the arteries. This arterial narrowing begins when men are in their 20s and is due mostly to cigarette smoking, high blood pressure, a genetic predisposition, high cholesterol or a combination of these four factors. As the blockage slowly progresses over the years, the arteries are unable to widen enough to permit increased blood flow to the penis.

ED is a common side effect of many prescription drugs. The most common offenders are medications for high blood pressure, heart ailments and allergies. Other culprits are medications prescribed to combat depression, especially the serotonin reuptake inhibitors (SSRIs) such as Prozac, Zoloft and Paxil.

Other causes.  Other causes of ED include excessive alcohol consumption, smoking (which impedes blood flow) and low levels of testosterone, the male sex hormone.

Less commonly, psychological factors such as fatigue, tension, stress, anger or depression can cause ED. However, psychological problems are rarely the sole cause of ED.

Last Updated: 1/7/2003
The Johns Hopkins University 1996-2003.  All rights reserved.   This information is not intended to provide advice on personal medical matters, nor is it intended to be a substitute for consultation.