COMT and Parkinson disease: Conventional pharmacotherapy for these diseases—such as dopamine replacement (levodopa), monoamine oxidase-B (MAO-B) inhibitors (selegiline, rasagiline), and COMT (catechol-O-methyltransferase) inhibitors (entacapone, tolcapone) for PD—primarily provides symptomatic relief rather than neuroprotection or disease modification.