A complex process involving psychological stimulus from the brain, adequate levels of the male sex hormone called testosterone, a normal nervous system, and healthy blood vessels in the penis chambers is required in order to achieve normal erections. In the soft (flaccid) state of the penis, the blood vessels inside the 2 chambers of the penis (corpora) are contracted and blood flows easily from the penis to the rest of the body. In the rigid state (erect) , the blood vessels in the chambers , under the influence of nerve impulses, become dilated, allowing more blood flow in the penis and also trapping blood in the penis, once the penis is fully erect. The trapping of blood in the penis increases the length, width, and temperature of the penis.

There are several risk factors for the development of ED. As men age, the level of circulating testosterone decreases, which may interfere with normal erection. While a low testosterone level itself is rarely the only cause of ED (5 percent or less), low testosterone can be an additional contributing factor in many men who have other risk factors for ED. Low levels of sexual desire, lack of energy, mood disturbances and depression can all be symptoms of low testosterone. A simple blood test can determine if the testosterone level is abnormally low, and testosterone can be replaced using a number of different delivery systems (e.g., injections, skin patches, and gels ) Of note, there is no FDA approved testosterone pill.

The most common cause of the development of ED is the presence of medical conditions such as high blood pressure, diabetes mellitus, renal disease, high cholesterol levels and cardiovascular disease. These medical conditions, acting over time, can lead to a hardening of the penile blood vessels, leading to restriction of blood inflow through the blood vessels. Surgery or radiation therapy for prostate , bladder, colon, or rectal cancer can also lead to the development of ED. Cryotherapy ( freezing of the Prostate ) for cancer is highly associated with ED.

Unhealthy daily habits can lead to degeneration of the erectile tissue and the development of ED. Cigarette smoking, illicit drug use or alcohol abuse, particularly over a long period of time, will compromise the blood vessels of the penis. Lack of physical exercise and a sedentary lifestyle will contribute to the development of ED. Psychological stressors, marital issues, and

psychogenic disorders can also cause ED. Correction of these conditions will contribute to overall health and may help correct mild ED. Medical treatment of many medical conditions can interfere with normal erections. Prescription drugs used to treat these risk factors listed above may also lead to or worsen ED

For most patients, the diagnosis will require a simple medical history, physical examination and a few routine blood tests ( blood sugar ( Hemoglin A1c ), cholesterol, lipid profile, PSA, testosterone, ect ). Several validated questionnaires help the clinician verify and grade the severity of the diagnosis. Most patients do not require extensive testing before beginning treatment. The choice of testing and treatment depends on the goals of the individual. If erection returns with simple treatment like oral medication and the patient is satisfied, no further diagnosis and treatment are necessary. If the initial treatment response is inadequate or the patient is not satisfied, then further steps may be taken. In general, as more invasive treatment options are chosen, testing may be more complex and involved.