Molecular model of Levodopa, or L-DOPA, a drug used in the management of Parkinson's disease. It works by increasing levels of dopamine in the brain. It is a prodrug, which means that it is administered in an inactive form, but once in the central nervous system (CNS), it is metabolized to dopamine. Dopamine is not administered directly because it is unable to cross the blood-brain barrier. The dopamine levels in people suffering from Parkinson's disease are known to be reduced and this is thought to be the cause of some of the symptoms of the disease.