The standard dose, the 50mg Viagra is sold over the counter as Viagra Connect. These medicines are called PDE5 inhibitors. How to get more bang for your buck Generic versions of Viagra sildenafil , Cialis tadalafil , and Levitra vardenafil have all become available in the last few years. Severe liver disease. And Viagra is no exception.Viagra comes as tablets that you take by mouth, when needed. Available strengths: 25 mg, 50 mg, mg Viagra comes in these strengths: 25 milligram (mg), 50 . Sildenafil oral tablet is available as a brand-name drug and as a generic drug. Brand names: Viagra, Revatio. Sildenafil comes in three forms: an oral tablet, an . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called .