L-DOPA (levodopa, 3,4-dihydroxy-L-phenylalanine). As a drug it is used to treat parkinsonism. L-DOPA is able to pass the blood-brain barrier as a prodrug and is decarboxylated in the brain to the neurotransmitter dopamine by the enzyme aromatic-L-amino-acid decarboxylase. In this way, L-DOPA can relieve some of the dopamine deficit seen in parkinsonism. A possible side effect of L-DOPA is a condition similar to amphetamine psychosis.