Nerve impulses transverse the length of the spinal cord to the pudendal nerve and on to the penis.  Smooth muscle within the walls of the penile arteries respond by relaxing.

Subsequently, the penile arteries dilate allowing up to eight times more blood to flow into the corpora cavernosum, (two parallel cylinders that transverse the length of the penis).

The cavernosum become engorged with blood expanding and lengthening the penis.

The expanding tissue then exerts a positive pressure compressing the veins that normally empty the blood from the penis, maintaining the blood in the penile tissue.

Vascular Disease is the leading cause of ED. Vascular disorders including arteriosclerosis (hardening of the arteries), hypertension, hypercholestremia and other conditions which interfere with the blood flow to the penis.  Additionally, "venous leakage" also contributes to poor erections.  This condition occurs when the penile veins are unable to constrict efficiently during an erection.  When these veins "leak" blood escapes to the periphery resulting in a poor erection

Diabetes is another common cause of ED. Approximately fifty percent of men with diabetes (insulin dependent) experience some degree of ED after the age of fifty-five.  Diabetes results in poor circulation and/or peripheral neuropathy.  When the nerves are involved sexual stimuli are not transmitted appropriately to or from the brain and ED develops.

Prescription medications often cause ED as a side effect.  Some two hundred known medications fall into this category including:

• Antihypertensives medications significantly:
1. beta-blockers e.g. Atenolol, Propanolol and Tenorium.
2. Diuretics medications e.g. HydroDiuril and Lasix.
3. Ace Inhibitors/Calcium Channel Blockers medications e.g. Vasotec, Lotension, Cardizem, Norvasc periodically cause ED, however, they are generally represent an excellent alternative medication for individuals with drug induced ED.
• Antidepressant/Antipsychotic medications of almost any label can also result in ED e.g. Prozac, Elavil, Zoloft, Thorazine, Haldol. Note: Many other medications in a variety of classes can periodically cause ED.  If you are taking a prescription medication or over-the-counter medication, regularly, please consult with your physician.  However, never alter a dosage or discontinue a medication without the advice of your physician.
• LH-RH Analogs/Antiandrogen medications e.g. Lupron Depot®, Eulexin, Nilandron®, Casodex®, etc.  These medications are used in the treatment of prostate cancer.  They function by decreasing the production of testosterone in the testes and adrennal glands.  The decrease in testosterone often results in ED.
• Chemotherapy/Radiation therapy are also significant contributors to ED.  These drugs/treatments are used in the treatment of cancer.

Substance Abuse can also negatively effect male potency.  The chronic use of cocaine, marijuana, alcohol, steroids etc. often results in ED, as well as a decrease in desire.  Excessive tobacco use can also attribute to ED by accentuating the effects of other risk factor such as vascular disease or hypertension.

Radical Pelvic Surgery also result in ED. Surgical procedures involving the prostate gland, bladder or colon may interfere with the nerves involved in the erectile response.  Radiation therapy for cancer may also effect the erectile process.

Neurological diseases such as multiple sclerosis, Parkinson's disease, spinal cord injuries, long term effects of diabetes can also result in the disruption of the normal sequence of events necessary for an erection to occur. 

Deficiencies in the Endocrine System are another source of ED. Low levels of testosterone or thyroid hormone can interfere with the stimulation process necessary in the erection sequence.  Excessive production of prolactin by the pituitary gland may contribute to decreased levels of testosterone resulting in a lack of desire.  Diabetes once again enters the scenario as it is classified as an endocrine disorder.

Psychological ED is usually diagnosed when no physical causes can be defined.  Pure psychological ED usually occurs suddenly without warning as opposed to physical ED that may gradually develop over years.  Some common causes of psychological ED are as follows:

• Performance anxiety is one of the most common causes of psychological ED.  When a man feels pressured to achieve or maintain an erection, he will commonly become anxious and nervous when in a sexually demanding situation.  Stress increases the body's production of catecholamines such as adrenaline and nor- adrenaline, which act as erection inhibitors.  The release of these inhibitors further contributes to failure resulting in more anxiety.  Therefore, the cycle begins, increased stress resulting in increased catecholomines that further inhibits the erectile process.
• Depression is another cause of psychogenic ED.  Unfortunately, many of the popular antidepressant medications (for a list see prescription medications in the next section) have side effects which include erectile failure.

Urethral Inserts consists of a disposable applicator, small enough to fit into the urethra.  The applicator is inserted into the urethra approximately one inch and the medication (prostaglandin E-1) is released.  As a result, an erection occurs lasting 30-60 minutes.  Patient acceptance is still an issue secondary to expense and the low success rate as compared to other treatments for ED. The inserts are available through the pharmaceutical company Vivus Inc.

Vacuum Therapy works by placing a cylinder with an attached pump over the penis.  The pump creates a vacuum in the cylinder, which pulls blood into the penis tocreate an erection.  The cylinder is then removed while simultaneously a constriction band is placed at the base of the penis.  This will usually keep the penis erect for up to thirty minutes, These devices range from $150.00-400.00 and can be purchased through Mentor Urology, POST-T-VAC, Inc., American Med Tech, Inc.

Hormonal Therapy is used to treat the small percentage of individuals who have abnormally low levels of testosterone. During the initial consultation a physician will likely order hormone tests (LH and Prolactin) first to exclude other causes of low testosterone levels.  If appropriate, testosterone is available in a transdermal adhesive patch.  The patch is available through Androderm (SmithKline Beecham) and Testroderm (Alza Pharmaceuticals), at a cost of $20.00 per patch.

Vascular Surgery may involve both the arterial and venous systems.  Venous ligation has been reported to be effective in patients with venous leakage.  However, it is often difficult to diagnose individuals with this condition given are current testing capabilities; therefore, it is difficult to predict their outcome prior to surgery.  Arterial revasculation procedures are limited to congenital or traumatic vascular abnormalities.  Similar to venous testing, complete standardization diagnostic testing has not been established, so difficulties persists in predicting surgical results.

Penile Implants requires surgical insertion of a prosthetic device.  Three forms of penile prosthesis are currently available flexible, malleable and inflatable.  Flexible or Malleable rods consist of two semi-rigid, flexible rods which make the penis firm enough for intercourse.  There are also inflatable prosthetic devices that produce a more natural erection.  When an erection is desired the pump (located in the scrotum) is squeezed, this in turn inflates a cylinder creating an erection.  Following intercourse, the pump is released and the penis returns too normal.  These devices have been associated with postoperative infections, mechanical failure, silicon particle shedding and the risk of the initial surgery.  These prosthetics are available through American Medical Systems and Mentor Urology.

Herbal Approaches are not currently regulated by the FDA so it is difficult to ascertain whether their hype is warranted.  Furthermore, these products tend to suggest an aphrodisiac effect (help with the loss of sexual desire) rather than improvement wit ED.

Psychotherapy and/or Behavioral Therapy have been found to be beneficial in treating ED.  Although the majority of causes of ED are physical, there are quite frequently underlying psychosocial factors involved as well.  Psychotherapy and/or behavioral therapy may be helpful in individuals whom no organic cause for ED has been detected.  Therapy often focuses on complications surrounding performance anxiety, dysfunctional relationships, loss of a partner, psychotic disorders, substance abuse, etc.

Partners can provide support for individuals with ED.  The condition affects the relationships of more than 50 million Americans.  If you are a partner, you can make a difference through support and education.  For a list of Impotence Anonymous (IA®) and I-ANON® chapters, call 1-800-669-1603 or email to.