Clonidine is a medication commonly used to lower blood pressure. It may be effective on its own, or be used in conjunction with other medication. It works by relaxing the walls of the blood vessels and slowing the heart rate. Clonidine requires a prescription and may not be purchased over-the-counter. It most commonly comes in the form of a pill. In some cases it may come in the form of a transdermal patch or epidural injection.