In the flaccid penis, the inflow and outflow are minimal (left). Impotence can also result from venous leak, in which tissue atrophy or scarring occurs within the penis, resulting in blood escaping from the penis similar to how air escapes from a leaking balloon. In small amounts, alcohol is a central anxiolytic and thus decreases the normal cerebral inhibition and provokes desire; its vasodilatory effect also enhances penile erection. This is an elegant description of the pharmacologic effects of alcohol. It provokes, and unprovokes: it provokes the desire, but it takes away the performance."

In Act II, Scene III of Shakespeare's Macbeth, a porter says to Macduff, "Drink (alcohol) is a great provoker of three things: nose-painting, sleep, and urine. If you suspect that your ED is associated with taking a prescription drug, discuss it with your physician. They include antidepressants (taken for depression and anxiety) and some of the medications used to treat pain, high blood pressure, stomach ulcer, and prostate cancer. However, several classes of drugs are known to cause impotence in some men. The mechanism of action is mostly unknown, and few well-controlled studies have examined how specific drugs affect sexual function. Impotence is a fairly common side effect of some prescription drugs. In rare cases, a tumor in the pituitary gland of the brain can produce an excessive amount of a hormone called prolactin that can suppress the production of testosterone and thereby cause loss of sexual drive as well as erectile dysfunction. A dysfunction in the thyroid gland resulting in either too much thyroid hormone (hyperthyroidism), or too little (hypothyroidism), may contribute to erectile dysfunction.

However, a low level of testosterone does decrease sexual desire, which ultimately affects the ability to achieve an erection. Although doctors once believed that a low level of the male sex hormone testosterone caused impotence, it is now generally recognized that testosterone is not directly involved in the physical process of an erection. Unfortunately, many men with diabetes are not aware that impotence is a potential complication of the disease. The damage to the nervous system, cardiovascular system and other major organs caused by diabetes can cause ED. However, the hormone deficiency alone doesn't cause impotence.

Diabetes is caused by a deficiency in insulin, a hormone that helps the body convert sugar (glucose) into energy. Impotence caused by diabetes can be related to both nerve damage and poor blood flow. In fact, about 50% of all diabetic men experience impotence. Diabetes is one of the most common causes of impotence. If the outflow channels remain widely open, the balloon can not be filled; this is analogous to impotence caused by venous leak seen in many men. During erection, the inflow is at its maximum, while the outflow is markedly reduced so that blood is retained in the erectile tissue to expand and lengthen the penis (right). However, in large amounts, alcohol is a strong sedative-hypnotic.