If you are a Mayo Clinic patient, this could include protected health information. This will increase the supply of blood to the lungs and reduce the workload of the heart. Tell your doctor or prescriber about all prescription, over-the-counter non-prescription , and herbal medications that you are taking. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it. The amount of medicine that you take depends on the strength of the medicine. If use of a nitrate-containing medication is considered medically necessary, you must wait 48 hours after the last dose of Viagra Sildenafil before taking a nitrate, and only under close medical supervision.He or she will tell you how much VIAGRA to take and when to take it. Get into the mood. You will not get an erection just by taking VIAGRA. You must be sexually stimulated for it to work. Take your time. VIAGRA usually starts to work within minutes. You may take it up to 4 hours before sexual activity. 25 milligrams (mg) 50 mg mg Typical dosages The following information describes commonly recommended dosages for ED. However, be sure to take the dosage your . Viagra (Sildenafil) belongs to a group of medications called phosphodiesterase type 5 inhibitors. It is used for the treatment of Erectile Dysfunction (male impotence). It helps to achieve and keep an erection sufficient for sexual activity. It does this by allowing a greater blood flow into the penis when a man is sexually aroused.