A medicine used for liver conditions is being added to a large UK trial investigating whether existing drugs can slow the progression of Parkinson’s disease.
Ursodeoxycholic acid, known as UDCA, became a candidate for further testing after Sheffield researchers studied its effects in tissue from people with Parkinson’s. The trial team is adding it as a third active treatment this month, alongside two medicines already under investigation.
The development is a step towards answering a question, not proof of a treatment. UDCA has not been shown to slow Parkinson’s progression, and people should not start taking it for Parkinson’s outside the research study.
From laboratory research to a larger trial
Parkinson’s is a progressive condition associated with the loss of nerve cells in part of the brain. Symptoms can include tremor, slow movement and muscle stiffness, although people’s experiences vary. Existing care can help manage symptoms, but a treatment that reliably slows the underlying progression remains the goal of research.
The Sheffield work began with a search through existing compounds using tissue from people with Parkinson’s. Researchers identified UDCA as a candidate because of its potential effects on mitochondria, the structures that help cells produce energy. Problems with mitochondrial function are thought to be relevant to the loss of nerve cells in Parkinson’s.
That possible mechanism is still being investigated. Evidence that a compound affects cells in the laboratory does not establish that it will protect nerve cells or change the course of the condition in patients.
An earlier, smaller study followed 30 people with Parkinson’s over 48 weeks. Participants were randomly assigned to UDCA or a placebo, an inactive treatment used for comparison. The main aim was to assess safety and whether the medicine was tolerated.
Researchers reported that UDCA was safe and well tolerated in that small study, although mild, temporary gastrointestinal side effects were more frequent in the UDCA group. Brain scans suggested changes consistent with improved cellular energy processes, and sensor measurements suggested possible improvements in aspects of walking. A standard clinical assessment of movement did not detect a difference between the groups.
Those findings were encouraging enough to justify further investigation, but the earlier study was not a definitive test of whether UDCA slows the disease. The larger trial is intended to address that remaining uncertainty.
How the new treatment group fits in
The study, called EJS ACT-PD, opened in 2025 with two active drug groups. One tests telmisartan, a medicine used for high blood pressure; the other tests terazosin, which is used for conditions including an enlarged prostate. Both are being investigated for their potential to affect Parkinson’s progression, not because that benefit has already been established.
UDCA was identified as a future addition when the trial opened. Its introduction this month will bring the number of active medicines being tested to three. The design allows treatments to be studied within the same trial framework rather than setting up a separate trial from scratch for each medicine.
New participants will be randomly allocated to a group for which screening shows they are eligible. There will be five groups: three receiving an active medicine and two receiving placebos. The additional placebo group is needed because UDCA has a different dosing schedule from the other two drugs.
Participants assigned to the UDCA schedule will take either the medicine or matching placebo tablets at three separate times during the day. They will continue their usual Parkinson’s care alongside the trial treatment. Neither participants nor the study team will know which treatment or placebo a person has been assigned while the trial is taking place.
Recruitment and patient safety
The latest plan is to recruit 2,000 participants across 40 hospital sites in the UK. As of the latest update, 26 sites had opened. More than 2,200 people had registered an interest in taking part, a figure that should not be confused with the number enrolled.
Only new participants screened after the UDCA group opens can be allocated to it, subject to the trial’s eligibility and safety checks. People cannot choose which treatment group they enter. The trial team advises existing participants not to withdraw in the hope of being reassigned to UDCA: those who withdraw cannot re-enter to be randomised again.
Anyone interested in the study can discuss it with their clinical care team. For people already taking part, questions about treatment or eligibility should go to their local trial team. The medicine’s existing use for liver conditions does not establish that it is effective or appropriate for Parkinson’s outside the carefully monitored trial.
Featured image: AI-generated illustration.
