You should only be treated with one of these products at a time. Ask your healthcare professional how you should dispose of any medicine you do not use. Sildenafil usually should not be taken more than once every 24 hours. Follow your doctor’s orders or the directions on the label. Remove the syringe from the bottle. From Mayo Clinic to your inbox Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health. Children 1 year of age and older weighing 20 kg or less—10 mg 3 times a day.Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the . 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. Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be.