ED can sometimes signal an underlying medical problem, like heart disease or diabetes , that needs to be treated separately. Tadalafil is another licensed oral medication that treats ED, but it lasts for much longer — up to 36 hours Viagra only lasts around four hours. If you have an erection that lasts more than 4 hours, get medical help right away. Men were also turning to unlicensed and potentially harmful remedies, such as Kamagra an oral jelly that claims falsely to contain the same ingredients as Viagra. Most will prescribe the 50mg tablet at first to patients who are just starting to take Viagra. · Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men. Another brand of sildenafil is Revatio, which is used to treat .  · Specifically, you may have a lower starting dosage than usual if you’re over age For example, a year-old might start at a dose of 50 milligrams (mg), while a year-old might have a. Generic Viagra (sildenafil) is an alternative to the branded Viagra drug that can be used for treating erectile dysfunction (ED). It’s now sold by many manufacturers, including online.