COMT and Parkinson disease: Since the introduction of levodopa in the 1960s (Fahn 2008), we have seen the development of dopamine agonist compounds (including ergot based and non-ergot-based drugs), adjuncts to the use of levodopa (DDC, COMT and MAO-B inhibitors) and a move away from the classical oral administration used in PD (including intraduodenal administration, subcutaneous infusion and transdermal application) (Armstrong and Okun 2020a, b; Bloem et al. 2021; Kalia and Lang 2015; Poewe and Mahlknecht 2020; Poewe et al. 2017).