Often, these are prescribed for chest pain called angina. Do not take other medicines unless they have been discussed with your doctor. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. If you experience a sudden loss of vision in one or both eyes, contact your doctor immediately. This site is intended only for U. Side Effects Along with its needed effects, a medicine may cause some unwanted effects. Use only the brand of this medicine that your doctor prescribed.Common Brands Viagra Drug Class PDE-5 inhibitor Controlled Substance Classification Not a controlled medication Generic Status Lower-cost generic available Availability . Generic version. Viagra is available in generic form called sildenafil. A generic drug is an exact copy of the active drug in a brand-name medication.  · Viagra; Descriptions. 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 .