The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. It works for up to 36 hours. Every batch of medications must go through rigorous analysis to ensure that every dosage is safe and consistent. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED. Goldstein said the drugs are largely made by “illicit narcotic labs.While some of what’s sold as generic Viagra online is fake, several reputable companies sell sildenafil online. Each of the companies below has been vetted by our team for medical and business. In fact, a recent review of studies found that some counterfeit drugs contained a very high, dangerous level of sildenafil that far exceeded a typical prescription dosage. In , the Missing: real. Rarely reported side effects include: an erection that will not go away (priapism). If you have an erection that lasts more than 4 hours, get medical help right away. If it is not treated right away, priapism can permanently damage your penis. sudden vision loss in one or both eyes.