The difference between a brand name medicine like Viagra and a generic one like Generic Viagra (Sildenafil) is in the name, shape and in the price. A generic drug like Generic Viagra is usually called by the name of the active ingredient Sildenafil while a manufacturer uses a brand name like Viagra. However, a manufacturer cannot possess a patent for a certain chemical agent, this is why manufacturers of generic medications like Generic Viagra can legally produce the so-called "generics". Generic Viagra is the same chemically as brand Viagra and since the active ingredient Sildenafil is identical, they have the same medical effect.