Participants are randomly allocated to one of two treatment groups. In one group, participants are given capsules of simvastatin to take orally (by mouth) for 24 months. In the other group, participants are given placebo (dummy) capsules to take orally for 24 months. At the start of the study, when they receive their medication, participants complete a number of questionnaires and motor (movement) tests (a walking test and a finger tapping test). Participants in both groups also attend a further 6 clinic visits after 1, 6, 12, 18 and 24 and 26 months, where they are asked about their health and any medication they are taking, as well as repeating the questionnaires and motor tests. For 4 of the clinic visits, the participants will be asked to attend in the 'OFF medication' state (having omitted their usual PD medication) so that the researchers can get a true picture of their disease without it being masked by their normal medication.

Inclusion Criteria:

• Diagnosis of idiopathic PD
• Modified Hoehn and Yahr stage ≤ 3.0 in the ON medication state
• Age 40-90 years
• On dopaminergic treatment with wearing-off phenomenon
• Able to comply with study protocol and willing to attend necessary study visits

Exclusion Criteria:

• Diagnosis or suspicion of other cause for parkinsonism
• Known abnormality on CT or MRI brain imaging considered to be causing symptoms or signs of neurological dysfunction, or considered likely to compromise compliance with study protocol
• Concurrent dementia defined by MoCA score <21
• Concurrent severe depression defined by MADRS score >31
• Prior intracerebral surgical intervention for PD including deep brain stimulation, lesional surgery, growth factor administration, gene therapy or cell transplantation
• Already actively participating in a research study that might conflict with this trial
• Prior or current use of statins as a lipid lowering therapy
• Intolerance to statins
• Untreated hypothyroidism
• End stage renal disease (creatinine clearance <30 mL/min) or history of severe cardiac disease (angina, myocardial infarction or cardiac surgery in preceding two years)
• eGFR <30 mL/min
• History of alcoholism or liver impairment
• Creatine kinase (CK) >1.1 x upper limit of normal (ULN)
• Aspartate transaminase (AST) or alanine transaminase (ALT) >1.1 x ULN
• Females who are pregnant or breast feeding or of child-bearing potential and unwilling to use appropriate contraception methods whilst on trial treatment
• Currently taking any medication contraindicated with simvastatin use (Appendix 2)
• Any requirement for statin use
• Regular participation in endurance or high-impact sports
• Unable to abstain from consumption of grapefruit-based products

The data sharing plans for the current study are unknown and will be made available at a later date

On application