Write down any symptoms you’ve had, including any that might seem unrelated to erectile dysfunction. Click here for an email preview. The elastic ring can remain in place up to 30 minutes. Slowly pull back the plunger until the required dose. Side effects Side effects of oral ED medicines are often mild.This medicine usually begins to work for erectile dysfunction within 30 minutes after taking it. It continues to work for up to 4 hours, although its action is usually less after 2 hours. . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 . Drug Images What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. Viagra.