MODEL RELEASED. Viagra pill held between a man's fingers. Viagra is the trade name for the drug sildenafil citrate, the first oral treatment for male impotence. It is used to treat erectile dysfunction. Viagra enhances the smooth muscle relaxant effects of nitric oxide, a chemical that is released in response to sexual stimulation. Relaxation of the smooth muscle allows blood to enter the penis, resulting in an erection. Viagra is made by Pfizer Pharmaceuticals.