L-DOPA (L-3,4-dihydroxyphenylalanine) is a chemical that made from, and used, as part of the normal biology of some animals and plants. Animals including humans, make it via biosynthesis from the amino acid L-tyrosine. Levodopa crosses the protective blood-brain barrier, whereas dopamine itself cannot. Thus, L-DOPA is used to increase dopamine concentrations in the treatment of Parkinson's disease and dopamine-responsive dystonia. Treatment was originally developed by George Cotzias.