The drug with the brand name VIAGRA has 50mg of the active component Sildenafil Citrate. It is produced by the pharmaceutical business Pfizer and is sold in packs of four tablets. By boosting blood flow to the penis during sexual stimulation, sildenafil helps men with erectile dysfunction (impotence) erect and keep an erection. It functions by preventing the breakdown of a substance called cyclic guanosine monophosphate (cGMP), which aids in relaxing the blood vessels of the penis, via an enzyme called phosphodiesterase type 5 (PDE5). Women and children should not use this drug; it should only be taken as prescribed by a doctor.