If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. In these studies, involving about patients, analyses of patient diaries showed no effect of VIAGRA on rates of attempted intercourse about 2 per week , but there was clear treatment-related improvement in sexual function: per patient weekly success rates averaged 1. If you need emergency medical care for a heart problem, it is important that your doctor knows when you last took sildenafil. If you are taking sildenafil to treat erectile dysfunction, follow your doctor’s directions and the guidelines in this paragraph. Tell your doctor if sildenafil is not working well or if you are experiencing side effects. · Viagra comes as an oral tablet that contains the active drug sildenafil. Sildenafil is also available in generic form. Viagra is classified as a phosphodiesterase type 5 (PDE5) inhibitor. Sildenafil tablets for erectile dysfunction come in different strengths ranging from 25mg to mg. The usual dose is 50mg, when you need it. Do not take it more than once a day. The dose can be increased to mg or decreased to 25mg depending on its effect. Take sildenafil up to 4 hours before you want to have sex. 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 .