COMT and Parkinson disease: 6,7-Dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline-1,3-dicarboxylic acid (B) (Figure 1), isolated from Mucuna pruriens, traditionally used for the treatment of Parkinson’s disease, and synthetized from L-DOPA, behaves as a peripheral catechol-O-methyltransferase inhibitor (COMTI).