Cialis, Viagra, Stendra and Levitra are the oral medications. They are popular pills to treat Erectile Dysfunction (ED). Erectile dysfunction is the inability to get or maintain a hard-on during sex. These drugs are usually known by their generic names: tadalafil (Cialis), avanafil (Stendra), sildenafil (Viagra), vardenafil (Levitra). One of the most popular drugs is Viagra dose of 100 mg.