Can we use existing drugs to treat Parkinson's?

What is a repurposed drug?

A repurposed drug is when an existing drug for one condition is used to treat a different condition. This process is known as 'drug repurposing'.

For example, a drug originally used to prevent seizures is now commonly being used to treat anxiety disorders.

Identifying which drugs can be repurposed

Researchers first gather evidence about whether a drug has the potential to be used to treat another condition. They do this by searching through existing research about the drug, and run experiments in the laboratory. Laboratory tests involve testing the drug in lots of different ways, including in cells and animals, to see how it's working. Advances in technology and artificial intelligence (AI) can also help researchers to identify the potential of a drug based on in-depth knowledge about how its chemical components work.

Once researchers have gathered all this information, they then need to see how effective the drug is in people.

Researchers can also use real-world evidence from people who are already taking a drug. For example, previous research examined 150,000 people who had been treated for an enlarged prostate. Half the group were on a drug called terazosin, and the study found that they were less likely to develop Parkinson's compared to people on an alternative medication. Researchers also found that people who had taken terazosin seemed to have less severe Parkinson's symptoms and slower progression. This drug is now in a clinical trial for Parkinson's, which you can read more about below.

Why do we repurpose drugs?

Developing new drugs can be a long and complicated process, taking around 10 to 15 years on average. We need ways to speed up this process. 

Repurposing drugs can help to do this. Part of developing a new drug is making sure that it's safe for people to take. Because these tests have already been done for a repurposed drug, it shortens the length of the development process and reduces the costs.  

Typically, there are 3 phases of clinical trials before a drug becomes available to the public:

• Phase 1 involves a small number of people and aims to check that a drug is safe.
• Phase 2 involves a larger group of people and aims to find the correct dose of a drug, look at potential side effects, and determine how well the drug works.
• Phase 3 is the final stage. The drug is tested in a large number of people to find out even more and prove that it is effective.

For repurposed drugs, we can shorten the clinical trial process. If there is enough safety evidence, the drug can move straight to phase 2 clinical trials.

Can repurposed drugs be used to treat Parkinson's?

There are multiple clinical trials happening to find out whether existing drugs for other conditions can be used to treat Parkinson's. 

Improving Parkinson's symptoms

We're currently funding a clinical trial to find out if a drug used to treat nausea and sickness can be repurposed to help manage visual hallucinations in people with Parkinson's. It's hoped that this drug can help improve the lives of the 1 in 4 people living with Parkinson's who experience visual hallucinations.

Find out more about the TOP HAT clinical trial and how to take part.

Slowing down or stopping Parkinson's

One exciting trial that we're currently funding is the Edmond J Safra Accelerating Clinical Trials for Parkinson's study (EJS ACT-PD). This is the largest UK clinical trial for Parkinson's to date and is revolutionising the clinical trial process. It's testing multiple repurposed treatments at the same time that could slow or stop Parkinson's.

You can read more about how the trial is designed in our blog about EJS ACT-PD.

When the trial launched in 2025, it started with 2 repurposed drugs:

• telmisartan, which is currently used to lower blood pressure 
• terazosin, used to treat an enlarged prostate. 

In September 2026, researchers started recruiting to test a third repurposed drug in the clinical trial. The drug is called ursodeoxycholic acid (UDCA). 

How might UDCA help in Parkinson's?

UDCA is currently used to treat certain liver conditions. Early evidence suggested that UDCA works by improving the health of the tiny batteries in our cells, called mitochondria. Mitochondria are responsible for producing the energy in our cells and we know that in Parkinson's, the mitochondria in dopamine-producing brain cells aren't working properly. 

Our blog explains in more detail why fixing mitochondria could be the key to Parkinson's.

In 2013, we funded researchers from the University of Sheffield who tested thousands of drugs in cells donated from people with Parkinson's. UDCA was one of these drugs, and they found that it could improve the problems that these cells had with their mitochondria. 

Since then, more studies have built on this evidence and found that UDCA could help to improve the health of mitochondria in Parkinson's.

Phase 2 clinical trial

In 2023, researchers published results from the UDCA in Parkinson's study. As it was a phase 2 trial, the study only included 30 people with Parkinson's.

The study aimed to look at whether:

• a high dose of UDCA was safe for people with Parkinson's
• UDCA was helping mitochondria in the area of the brain affected by Parkinson's
• and if symptoms improved in people who had taken UDCA.

The researchers found that UDCA was safe and people had few side effects. From brain scans, they could see that mitochondria were working better in the area of the brain affected by Parkinson's, called the substantia nigra. The results didn't show an improvement in people's Parkinson's movement symptoms when they were measured using a traditional clinical assessment scale called MDS-UPDRS. But researchers did find that people who had taken UDCA experienced improvements in the way they walked (their gait) when measured using a wearable motion sensor.

Read more about the results of the UDCA in Parkinson's study in our news article.

What's next?

We know that UDCA is safe in people with Parkinson's and is having an effect in the area of the brain that it's designed to target. But can UDCA improve symptoms in Parkinson's and slow down the progression of the condition?

The EJS ACT-PD trial will aim to answer this question by looking at how the drug works in a much larger group of people. 

EJS ACT-PD is just one of the ongoing clinical trials investigating whether repurposed drugs can be beneficial treatments for Parkinson's. Repurposing drugs can help us to accelerate the search for new treatments to manage Parkinson's symptoms, and even slow or stop the condition.