These medicines are called PDE5 inhibitors. Its effects might last longer if you have mild to moderate ED. Medicines that you take by mouth are called oral medicines. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. This medicine works best when you take it on an empty stomach an hour before sex.When you get Viagra from the pharmacy, the pharmacist will add an expiration date to the label on the bottle. This date is typically 1 year from the date they dispensed the medication. Viagra may be available through a mail-order pharmacy. Using this type of service may help lower the drug’s cost and allow you to receive your medication without leaving home. Get drug information. Search for a drug by name or NDC number and get complete drug information. It’s like the printout attached to your refill—only electronic. Help me find my .