l-dopa (ĕl-dō´pə), drug used to alleviate some of the symptoms of Parkinson's disease, particularly trembling, rigidity, and slow movements; the drug is also called levodopa. Parkinson's disease results when the concentration of dopamine in the brain is depleted (see catecholamine). Medical administration of dopamine itself is ineffective since that chemical apparently does not enter the brain from the blood. A metabolic precursor of dopamine, l-dopa does enter the brain via the bloodstream and is probably converted into dopamine there. Because there are many brain disorders with similar symptoms, many patients do not show any improvement when treated with the drug. Furthermore, virtually all patients on l-dopa experience side effects including nausea, loss of appetite, cardiac irregularities, and psychological changes.