Background: There is evidence from controlled studies that in PD patients with motor fluctuations, the addition of a COMT-inhibitor (entacapone, tolcapone, opicapone) or a dopamine agonist (ropinirole, pramipexole, rotigotine, apomorphine) can reduce off-time and improve on-time without troublesome dyskinesia. Here, COMT is linked to Parkinson disease.