 Parkinson's disease, a degenerative condition causing tremor and motor impairment, is caused by a loss of dopamine-secreting neurons in an area of the midbrain called the substantia nigra.Its metabolic precursor L-DOPA can be manufactured; "Levodopa", a pure form of L-DOPA, is the most widely used treatment for Parkinson's.There is evidence that schizophrenia involves altered levels of dopamine activity, and most antipsychotic drugs used to treat this are dopamine antagonists which reduce dopamine activity.