This medicine works best when you take it on an empty stomach an hour before sex. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. Its effects often last for 4 to 5 hours. You may opt-out of email communications at any time by clicking on the unsubscribe link in the e-mail. Oral medicines for ED usually work well and cause few side effects. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction.1. How it works Sildenafil may be used to treat erectile dysfunction (ED or impotence) in men (Viagra brand) or pulmonary arterial hypertension in both men and women (Revatio brand), depending on the brand. Sildenafil blocks the action of an enzyme known as cGMP-specific phosphodiesterase type-5 (PDE-5). Sildenafil comes in three forms: an oral tablet, an oral suspension (liquid), and an injection that’s only given by a doctor. Sildenafil oral tablet is used to treat erectile dysfunction (ED.  · Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly.