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. Take sildenafil as needed before sexual activity. The amount of medicine that you take depends on the strength of the medicine. If you experience a sudden loss of vision in one or both eyes, contact your doctor immediately. Call your doctor right away if you have blurred vision, confusion, dizziness, faintness, or lightheadedness when getting up from a lying or sitting position suddenly, sweating, or unusual tiredness or weakness. If you already use medicine for high blood pressure hypertension , sildenafil could make your blood pressure go too low.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 lungs, causing shortness of breath, dizziness, and tiredness).  · Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where this enzyme works. Sildenafil oral tablet is used to treat erectile dysfunction (ED). It’s also used to treat pulmonary arterial hypertension (PAH). What is sildenafil? Sildenafil is a prescription drug. It.