Viagra is the brand name of the drug Sildenafil Citrate, which is used for the treatment of erectile dysfunction. In 1998, Viagra became the first drug officially approved for treatment of erectile dysfunction in the United States. It was shown to be successful in 4 out of 5 men. Viagra comes in pills of 25mg, 50mg or 100mg each, 50mg being the recommended dose for most men. The patient should take 1 pill about 30 minutes before sexual activity in order to be able to have an erection when being  stimulated. The drug remains effective for as long as 4 hours.