Viagra (sildenafil citrate) can be taken by male patients diagnosed with erectile dysfunction provided that they follow all the recommendations of your health care provider. Viagra is available by a prescription and comes in diamond-shaped blue tablets of 25 mg, 50 mg, and 100 mg. Combining Viagra with certain medicines may result in a sudden drop in blood pressure. Make sure you avoid using isosorbide mononitrate, nitrates and isosorbide dinitrate as they can make your treatment less efficient by causing dangerous health effects. Your health care provider is supposed to know as much as possible about your medical history to determine the right dose to prescribed, it’s especially important to mention kidney disease, very high or low blood pressure, eye problems, bleeding disorders, coronary artery disease, penis conditions, blood system cancers, recent stroke, recent heart attack, sickle cell anemia, active stomach ulcers, heart failure, or liver disease in case you have or ever had those conditions. Viagra is not known to cause serious side effects too often, but such mild side effects as headache, muscle ache, stuffy nose, or backache are quite common.