When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction. An inherited eye disease that affects the retina. When hypertension occurs in the lungs, the heart must work harder to pump enough blood through the lungs. Vardenafil usually works for 4 to 5 hours. If you have an erection that lasts more than 4 hours, get medical help right away.As an alternative to Viagra, a person may wish to try any of the following: Alternative oral drugs: Including vardenafil, tadalafil, and avanafil. Nonoral drugs: Such as penile self injections. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Cialis is only available by prescription in the United States. Viagra: Additionally, a study from Trusted Source. found that combining L-arginine and sildenafil (Viagra) worked better for.