A wide variety of physical and emotional risk factors can contribute to erectile dysfunction. They include:

* Physical diseases and disorders. Chronic diseases of the lungs, liver, kidneys, heart, nerves, arteries or veins can lead to impotence. So can endocrine system disorders, particularly diabetes. The accumulation of deposits (plaques) in your arteries (atherosclerosis) also can prevent adequate blood from entering the penis. And in some men, erectile dysfunction may be caused by low levels of the hormone testosterone (male hypogonadism).
* Surgery or trauma. Damage to the nerves that control erections can cause erectile dysfunction. It may result from an injury to the pelvic area or spinal cord. Surgery to treat bladder, rectal or prostate cancer also can result in erectile dysfunction. Prolonged bicycle riding also can cause a temporary problem.
* Medications. A wide range of drugs — including antidepressants, antihistamines and medications to treat high blood pressure, pain and prostate cancer — can cause erectile dysfunction by interfering with nerve impulses or blood flow to the penis. Tranquilizers and sleeping aids also may pose a problem.
* Substance abuse. Chronic use of alcohol, marijuana or other drugs often causes erectile dysfunction and decreased sexual drive. Excessive tobacco use also can damage penile arteries.
* Stress, anxiety or depression. Psychological conditions also contribute to some cases of erectile dysfunction.

Source: mayoclinic.com