Sildenafil citrate, sold under several brand names that vary from Viagra to Revatio and may also be found under its generic names such as Silagra, Kamagra, Caverta, Vigora, Zenegra and others. Sildenafil citrate is used to treat erectile dysfunction (old name impotence) in adult men. It is prescribed by doctors to help men with erectile problems which can be caused due to age, stress, social pressures or other physiological and psychological reasons. Erection lasting not longer than four hours.