What does viagra do? Viagra, sold under the brand name Viagra, used to treat male sexual function problems like impotence or erectile dysfunction-ED. The medicine comes under a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. Viagra can be taken orally or injected into a vein. It increases the blood flow to the penis to help a man get and keep an erection. The use of Viagra...