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Medical history is important for the doctors to know if any conditions might be causing the impotence. You will be asked about your sex life, including the quality of your sexual relationship. You will be examined to look for evidence of medical problems. Blood test for sugar, cholesterol and certain hormones will be checked.
Additional test occasionally will be made by your doctor like nocturnal penile tumescence to determine how often you get erections while you sleep. Another test is called Doppler ultrasound of blood vessels in the penis which measures how well the blood is flowing.

Although extensive testing may not be necessary your doctor will review the medications you take including herbal remedies. There is no specific reason why you have impotence but there are many treatments that works well no matter what the cause.