Participants who wish to be considered for inclusion in the trial will be screened for eligibility at the National Hospital for Neurology and Neurosurgery, according to inclusion and exclusion criteria. A narrative of what trial participation entails together with the participant information sheet will be used to educate potential participants. Each patient will be aware that they have a 50% chance of being allocated active drug or placebo. They will confirm their willingness to attend the clinic after an overnight period without their conventional PD medication. As part of the informed consent, the contact details of the research team will be given to each patient.