Recent heart or blood vessel problems. Tadalafil Cialis. Sildenafil Viagra. Do not mix the liquid with other medications or add anything to flavor the medication. You’ll soon start receiving the latest Mayo Clinic health information you requested in your inbox. This medicine also works best when you take it an hour before sex on an empty stomach. · Viagra; Descriptions. 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. The penis is one of the areas where . Same Day Rx Delivery · Convenient Locations · Hour Locations · Rx Savings Finder. 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 is approved for this use .