Comtan is a drug that is used to treat patients with Parkinson's disease. It inhibits catechol-O-methyltransferase (COMPT). It is often used in combination with Carbidopa and Levodopa to treat the symptoms that arise when the effect of the two medicines used to treat Parkinson's disease wear off. Comtan works by enabling higher amounts of both the Carbidopa and the Levodopa to reach the brain, where they will be able to take effect. Comtan taken on its own has no effect on Parkinson's disease.