Viagra (sildenafil) belongs to the class of phosphodiesterase (PDE) inhibitors and can be used for the treatment of erectile dysfunction (impotence) in men unable to get an erection and complete sexual intercourse. You must warn your doctor if you are taking any nitrate-based drugs that can come as sublingual tablets, ointments, tablets, sprays, patches, or pastes. It's not safe to combine nitrate based meds with Viagra as a sudden drop in blood pressure is possible. Always make sure you tell your health care provider about any other medications you are using at the moment -such as HIV protease inhibitors, erythromycin, certain antifungals, amlodipine, barbiturates, beta blockers, anticoagulants, bosentan, other erectile dysfunction meds, efavirenz, rifabutin, alpha blockers, seizure medications, nevirapine, rifampin, medications for high blood pressure, or cimetidine. It's also important for your doctor to know if you have any risk factors for developing sudden vision loss - such as smoking, diabetes, heart disease, high cholesterol, pre-existing eye problems, being over 50 years old, or high blood pressure. In that case you may be recommended an alternative to make sure you do not develop any serious health effects.