John’s wort. Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. From Mayo Clinic to your inbox Sign up for free and stay up to date on research advancements, health tips, current health topics, and expertise on managing health. Vardenafil usually works for 4 to 5 hours. If you have trouble quitting, get help. If it is not treated right away, priapism can permanently damage your penis sudden vision loss in one or both eyes.Sildenafil is a prescription drug. It comes in the form of a tablet and suspension (liquid). Both are taken by mouth. It also comes in an intravenous (IV) form, . Sildenafil (Viagra) Tadalafil (Adcirca, Cialis) Vardenafil (Levitra, Staxyn) Avanafil (Stendra) All four medications enhance the effects of nitric oxide — a natural . The Savings Offer and Program expire on 12/31/ For further information, call , visit test1.ru, or write: Viatris Inc., P.O. Box , Mission, KS .