Viagra patent expired on June 22, 2013. Since then, other manufacturers are allowed to produce and distribute their own variants of Viagra. Generic Viagra used as active ingredient sildenafil citrate, Viagra like the original or "brand". The difference lies in the accompanying excipients active (the excipients help the active ingredient to be absorbed by the body). Health checks on those who undergo brand drugs, the price difference is that generics do not require an initial investment in research (using an active ingredient already developed by others) and usually spend much less money on marketing. That allows generics are cheaper than the original but have the same function.