Medicines that you take by mouth are called oral medicines. They're often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction (ED). Oral medicines for ED usually work well and cause few side effects.

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. This boosts blood flow and helps you get an erection from sexual activity.