Generic Sildenafil Citrate (popular with the name Viagra) is used to treat the problem of Erectile Dysfunction (ED) in men. It works by enhancing the blood flow to the penis. A single pill of generic Sildenafil Citrate gives an erection which lasts for 5-8 hours. It is advised to take not more than one pill of this medicine in the 24 hour time period. For better results, take this pill approximately 1 hour before any sexual activity.