Clonidine lowers blood pressure by decreasing the levels of certain chemicals in your blood. This allows your blood vessels to relax and your heart to beat more slowly and easily. Clonidine is used to treat hypertension (high blood pressure). The Kapvay brand of clonidine is used to treat attention deficit hyperactivity disorder (ADHD). Clonidine may also be used for purposes not listed in this medication guide.