Vascular Disease is the leading cause of Impotence. 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 Impotence. Approximately fifty percent of men with diabetes (insulin dependent) experience some degree of Impotence 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 Impotence develops.

Prescription medications often cause impotence 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 Impotence, however, they are generally represent an excellent alternative medication for individuals with drug induced Impotence.
   
• Antidepressant/Antipsychotic medications of almost any label can also result in Impotence e.g. Prozac, Elavil, Zoloft, Thorazine, Haldol. Note: Many other medications in a variety of classes can periodically cause Impotence.  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 Impotence.
• Chemotherapy/Radiation therapy are also significant contributors to Impotence.  These drugs/treatments are used in the treatment of cancer.

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

Radical Pelvic Surgery also results in impotence. 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 affect 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 is another source of Impotence. 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 Impotence is usually diagnosed when no physical causes can be defined.  Pure psychological Impotence usually occurs suddenly without warning as opposed to physical Impotence that may gradually develop over years.  Some common causes of psychological Impotence are as follows:

• Performance anxiety is one of the most common causes of psychological Impotence.  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 Impotence.  Unfortunately, many of the popular antidepressant medications (for a list see prescription medications in the next section) have side effects, which include erectile failure.

Anatomical Deviation of the Penis, Peyronies Disease, may also cause Impotence.  This condition usually develops from an inflammatory process and results in fibrous scaring of the penis.  (The cause of this process is not yet understood)  However, when an erection does occur, there is a bending of the penis secondary to the scar tissue.  This curvature may interfere with erectile capacity and/or ejaculation.