This medicine is used to treat impotence (erectile dysfunction) in men.Store at 77 degrees F.How much medicine you take and how often you take it depends on many factors, including the condition being treated and the age and weight of the patient. If you have any questions about the amount and/or frequency of the medicine you are taking, talk with your health care provider. Carefully read the information provided with this medicine and reread it each time you get this prescription refilled. Take this medicine exactly as prescribed by your health care provider. This medicine should be taken on an as needed basis, about 1 hour before sexual activity. However, this medicine can be taken anywhere from 30 minutes to 4 hours before sexual activity. Do not take this medicine if you are currently taking medicines containing nitrates. Stop using this medicine and contact your health care provider if chest pain, dizziness, or nausea occur while engaged in sexual activity. If an erection last longer than 4 hours, seek medical attention at once. If prolonged erection is not treated immediately, damage to the penile tissue and loss of potency could result. This medicine offers no protection against sexually transmitted disease. Use condoms to guard against any sexually transmitted disease. Newborns, children, and women should not use this medicine. This medicine may cause dizziness or blurred vision. Use caution while driving or performing other tasks requiring alertness, coordination, or physical dexterity. Patients with previous medical conditions should talk with their health care provider before taking this medication. Do not take more medicine than prescribed unless advised to do so by your doctor or health care provider. Contact your health care provider at once if you feel you have used too much of this medicine. Do not take any other over-the-counter or prescription medications without talking with your doctor.Do not take this medicine if you are allergic to any ingredient in this medicine you are currently taking medicine that contain nitratesBefore using this medicine, tell your health care provider about any of the following: if you are taking any prescription medicine (especially ritonavir), nonprescription medicine, herbal preparation, or dietary supplement if you have a history of heart disease or heart failure if you have had a heart attack, stroke or other heart problems within the last 6 months if you have uncontrolled high blood pressure if you have low blood pressure if you have disease of the retina if you have a bleeding disorder if you have peptic ulcers if you have a deformed penis or conditions that may cause a prolonged erection (such as sickle cell anemia or leukemia) if you have any other medical conditionThis medicine should not be generally used in men for whom sexual activity is inadvisable because of their underlying cardiovascular status. This medicine should be prescribed with extreme caution to patients who have suffered a myocardial infarction, stroke, or life-threatening arrhythmia within the last 6 months; patients with cardiac failure or coronary artery disease causing unstable angina and patients with retinitis pigmentosa.Most severe: Fainting; chest pain; changes in heartbeat; severe allergic reactions (rash; hives; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue).Most common: Headache; flushing; indigestion; painful, prolonged erection; respiratory tract infection; back pain; flu like symptoms (fever, chills, sore throat); joint pain.Other: Stuffy nose; urinary tract infection; eye sensitivity to light; blurred vision; diarrhea; dizziness; rash.