There is only one way to reply to a forum advert: What is Viagra? Viagra (sildenafil) relaxes muscles found in the walls of blood vessels and increases blood flow to particular areas of the body. Viagra is used to treat erectile dysfunction (impotence) in men. Another brand of sildenafil is Revatio, which is used to treat pulmonary arterial hypertension and improve exercise capacity in men and women. This page contains specific information for Viagra, not Revatio. Do not take Viagra while also taking Revatio, unless your doctor tells you to. Important information Some medicines can cause unwanted or dangerous effects when used with Viagra. Tell your doctor about all your current medicines, especially riociguat (Adempas) and nitrates. Do not take Viagra if you are also using a nitrate drug for chest pain or heart problems, including nitroglycerin, isosorbide dinitrate, isosorbide mononitrate, and some recreational drugs such as "poppers". Taking sildenafil with a nitrate medicine can cause a sudden and serious decrease in blood pressure. Contact your doctor or seek emergency medical attention if your erection is painful or lasts longer than 4 hours. A prolonged erection (priapism) can damage the penis. Stop using Viagra and get emergency medical help if you have sudden vision loss.