DDC and Parkinson disease: Levodopa (L-dopa) is the most widely used agent for the symptomatic relief of Parkinson's disease.Levodopa is the naturally occurring precursor amino acid for dopamine and the main therapeutic agent for neurologic disorders due to dopamine depletion, such as Parkinson's disease.Levodopa is converted to dopamine via the action of a naturally occurring enzyme, DOPA decarboxylase.