Tolcapone is a drug that inhibits the enzyme catechol-O-methyl transferase (COMT). It is used in the treatment of Parkinson's disease as an adjunct to levodopa/carbidopa medication. It is a yellow, odorless, non-hygroscopic, crystalline compound with a relative molecular mass of 273.25. The chemical name of tolcapone is 3,4-dihydroxy-4’-methyl-5-nitrobenzophenone. Its empirical formula is C14H11NO5.