Tolcapone (3,4-dihydroxy-4′-methyl-5-nitrobenzophenone) was approved in 1997 by the European Medicines Agency and in 1998 by the Food and Drug Administration as the first levodopa add-on catechol-O-methyltransferase (COMT) inhibitor for the treatment of Parkinson’s disease (PD) patients with motor fluctuations [1]. This evidence concerns the gene COMT and Parkinson disease.