The nonprotein amino acid, 3,4-dihydroxyphenylalanine (L-DOPA) (Fig. 1) is present in high concentrations (about 3–6%) in Mucuna spp. The in vitro addition of L-DOPA to the red blood cells from individuals deficient in glucose 6-phosphate dehydrogenase decrease the glutathione content in red blood cells and this ultimately induces the favisum (hemolytic anemia; breakup of red blood cells). The inclusion of L-DOPA in fish feed has been reported to signifi- cantly reduce the growth performance. L-DOPA is susceptible to oxidation, giving a semiquinone that complexes with proteins. This decreases protein digestibility. On the other hand, it has been used for the treatment of Parkinson’s disease because of its being a precursor of dopamine, a neurotransmitter.