Lastly, although sildenafil is considered interchangeable with brand Viagra, they do have slightly different inactive ingredients. The announcement from Teva can be seen here. Its effects might last longer if you have mild to moderate ED. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. Side effects Side effects of oral ED medicines are often mild. Vardenafil usually works for 4 to 5 hours. You can take it in a small dose daily or in a larger dose as needed.When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side . Revatio is available as a generic under the name of sildenafil (20mg tablet). There is also a generic version of Viagra available, under the name sildenafil, in 25mg, . If you’re holding out for a generic version of branded Viagra, you won’t have to wait much longer. Teva Pharmaceuticals plans to release its generic of the “little blue .