d-DOPA (d-3,4-dihydroxyphenylalanine; dextrodopa) is similar to l-DOPA (levodopa), but with opposite chirality. Levo- and dextro- rotation refer to a molecule's ability to rotate planes of polarized light in either direction. Whereas l-DOPA is moderately effective in the treatment of Parkinson's disease (PD) and Dopamine-responsive dystonia (DRD) by stimulating the production of dopamine in the brain, d-DOPA is biologically inactive.