Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Do not take a double dose to make up for a missed one. Ask your pharmacist for a list of the ingredients. Sexual activity may be a strain on your heart, especially if you have heart disease. You are encouraged to report adverse events related to Viatris products by calling U.Viagra; Descriptions. Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called . In most countries, including the United States, Viagra is not available without a prescription. However, in , Viagra became available over the counter in the . Tips Response/effectiveness Interactions 1. How it works Sildenafil may be used to treat erectile dysfunction (ED or impotence) in men (Viagra brand) or pulmonary arterial .