Patient description: The patient is a 55-year-old man who was recently diagnosed with Parkinson's disease. He is complaining of slowness of movement and tremors. His disease is ranked as mild, Hoehn-Yahr Stage I. His past medical history is significant for hypertension and hypercholesterolemia. He lives with his wife. They have three children. He used to be active with gardening before his diagnosis. He complains of shaking and slow movement. He had difficulty entering through a door, as he was frozen and needed guidance to step in. His handwriting is getting smaller. He is offered Levodopa and Trihexyphenidyl. He is an alert and cooperative man who does not have any signs of dementia. He does not smoke or use any illicit drugs.

Clinical trial eligibility criteria: eligible ages (years): 18.0-75.0,  Parkinson's Disease • Diagnosis of Parkinson's disease: PD is a clinical diagnosis as defined by the Queen Square Brain Bank (bradykinesia defined as slowness of initiation of voluntary movement with progressive reduction in speed and amplitude on repetitive actions and at least one of the following: Rigidity, 4-6 Hz rest tremor). The diagnosis will have been made by the treating clinician and confirmed by the PI on site after review of the clinical history, examination findings and response to PD medication. The Queen Square brain bank MAY be used to help assist in the diagnosis although this need not be a formal and the relevance of a positive family history of PD, or a confirmed genetic basis for an individual's symptoms will be evaluated in the context of other clinical features in determining diagnosis and eligibility Diagnosis of Parkinson's disease ≤ 3 years ago by a clinician with particular expertise in the diagnosis and treatment of movement disorders (typically one of the PIs or their consultant colleagues). The date of diagnosis will be verified by a review of the medical records Subjective improvement of motor impairment on dopaminergic medication, confirmed by PI through personal examination and/or review of medical records Hoehn and Yahr stage ≤ 2.5 in the practically defined "ON" medication state. This implies that all patients will be mobile without assistance during their best "ON" medication periods Ability to take study drug Ability to communicate in English Age 18 yr of any gender Documented informed consent to participate Able to comply with study protocol and willing to attend necessary study visits  Diagnosis or suspicion of other cause of parkinsonism such as Multiple system atrophy (MSA) or progressive supranuclear palsy (PSP), drug induced parkinsonism, dystonic tremor or essential tremor will not be recruited Known abnormality on CT or MRI brain imaging considered likely to compromise compliance with trial/protocol/31P-MRS acquisition Known claustrophobia or other reasons why patient could not tolerate or be suitable for 31P-MR Spectroscopy (31P-MRS) Current or previous exposure to UDCA Current or previous diagnosis of liver disease judged to be significant by the clinical investigator, in particular Primary Biliary Cholangitis (previously referred to as Primary Biliary Cirrhosis, PBC) Prior intracerebral surgical intervention for PD (including deep-brain stimulation). Patients who have previously undergone deep brain stimulation, intracerebral administration of growth factors, gene therapies or cell therapies will not be eligible Already actively participating in a trial of a device, drug or surgical treatment for PD History of alcoholism Women of child bearing potential (WOCBP)