RecruitingPhase IIInterventional

A clinical trial to explore the potential of ondansetron for treating hallucinations in people with Parkinson’s disease

Many people living with Parkinson’s disease experience visual hallucinations, such as seeing things that are not really there. These can be frightening and stressful. Current medications often cause severe side effects, like extreme sleepiness, worsening movement problems, or falls. This clinical trial, led by University College London and funded by Parkinson's UK, explores whether a drug called ondansetron can help. Ondansetron is already widely used in the NHS to treat nausea and vomiting. Early evidence showed it might clear up hallucinations without worsening Parkinson’s symptoms. In this study, participants take either ondansetron or a dummy tablet (placebo) for 12 weeks. Researchers will track side effects and symptom changes through clinic visits and phone check-ins. If successful, this trial could lead to a safe, low-cost treatment to improve daily life for thousands of people with Parkinson's across the UK.

At a glance

Status

Recruiting

Phase

Phase II

Sponsor

PRIMENT CTU

Enrolment target

216

Start

01 Apr 2020

Estimated completion

31 Jan 2028

Parkinson's hallucinations

What is this study about?

Living with Parkinson’s disease involves more than just movement symptoms like tremors or stiffness. Around three in four people with Parkinson’s will see things that are not really there, known as visual hallucinations. These experiences can be distressing, affect overall quality of life, and put a huge strain on families and carers.

Right now, doctors have limited treatment options on the NHS. The drugs currently used are called antipsychotics. While they can sometimes help, they carry substantial risks. They can cause drowsiness, increase the chance of falls, and even make Parkinson’s movement issues or memory problems worse. A safer, gentler option is urgently needed.

Ondansetron is an affordable medicine routinely used in hospitals to prevent nausea and vomiting after surgery. Smaller studies in the past suggested it could safely reduce or stop hallucinations without harming movement or memory. This Phase II clinical trial aims to test ondansetron in a larger group of people across the UK to confirm whether it is safe and effective.

Key takeaways

Testing ondansetron, a well-known anti-sickness drug, to treat visual hallucinations in Parkinson’s.
Open to adults aged 55 and over who experience hallucinations at least weekly.
Involves taking study tablets daily for 12 weeks, with follow-ups over 24 weeks.
Standard rescue medication remains available if hallucinations become distressing.
Funded by Parkinson's UK and run across participating NHS clinics.

Who may be eligible?

This trial is open to adults aged 55 and older who have a confirmed diagnosis of Parkinson’s disease. You must have been experiencing visual hallucinations at least once a week over the past month. Your usual Parkinson’s medications must also have been on a stable dose for at least four weeks before joining.

To ensure your safety, certain people cannot join. This includes anyone with very slow heart rates, specific heart rhythm problems detected on an ECG (heart trace), or severe liver disease. You also cannot take part if you have taken antipsychotic medication in the last two weeks or are taking specific medicines such as apomorphine.

If you find it difficult to give consent yourself due to memory or thinking challenges, a family member or legal representative can help discuss and confirm your participation.

Could this study suit you?

Answer these quick questions to see if you may be eligible. This is a guide only — the research team makes the final call.

I am aged 55 or older with a confirmed diagnosis of Parkinson's disease.
I see things that are not there (visual hallucinations) at least once a week.
My daily Parkinson's medication doses have stayed the same for at least 4 weeks.
I have not taken antipsychotic medicines in the last 2 weeks.
I do not have severe liver disease or known serious heart rhythm problems.

Answer every question to see your result.

What does participation involve?

Taking part in the trial lasts around six months (24 weeks) in total. You will be randomly chosen by a computer system to receive either ondansetron tablets or dummy tablets (placebo). Neither you nor your research doctor will know which one you are taking. However, if your hallucinations become too distressing, usual NHS rescue medication will still be available so you are never left unsupported.

You will take the tablets daily for 12 weeks. During the first six weeks, the dose is gradually increased from one tablet up to a maximum of three tablets, with regular phone calls at weeks two and four to check for side effects. You will attend clinic visits for health checks and blood tests at week 6 and week 12. After you finish the medication, the study team will call you at weeks 16 and 24 to see how you are doing.

Potential risks and benefits

Ondansetron is an established medicine with a known safety profile, but it can cause side effects. The most common side effect is constipation, which is already a frequent challenge for people with Parkinson's; the study team will increase your dose slowly to help manage this. While you might not benefit personally, the treatment may help reduce or stop distressing hallucinations. You are completely free to leave the trial at any point, and choosing to stop will not affect your standard NHS care in any way.

Locations (12)

Some site locations are approximate. We're improving this — please verify with the trial team before travelling.

Leonard Wolfson Experimental Neurology Centre
City only
Epsom, England
Salford Royal NHS Foundation Trust
City only
Manchester, England
Pennine Acute Hospitals NHS Trust
City only
Bury, England
Cambridge University Hospitals NHS Foundation Trust
Unverified
Cambridge NO COUNTRY SPECIFIED, assuming England, England
Royal Bournemouth and Christchurch Hospitals NHS Foundation Trust
City only
Bournemouth, England
Northumbria Healthcare NHS Foundation Trust
City only
Newcastle upon Tyne, England
Royal Devon and Exeter NHS Trust
Unverified
Exeter, England
Royal United Hospitals Bath
Unverified
Bath, England
Wrexham Maelor Hospital
Unverified
Wrexham, Wales
Ysbyty Gwynedd
Unverified
Bangor, Wales
LLandudno Hospital
Unverified
Llandudno, Wales
Holyhead Hospital
Unverified
Holyhead, Wales

Common questions

Will I definitely receive the active trial medicine?

Not necessarily. Half of the participants take ondansetron and half take an identical dummy tablet (placebo). This helps researchers clearly prove whether the medicine works.

What happens if my hallucinations get worse during the study?

Your safety and comfort come first. Standard NHS medication (quetiapine) is available during the trial if you need extra support for distressing symptoms.

Will taking part interfere with my normal Parkinson’s treatments?

No. You will continue taking your regular Parkinson's medications as normal, as long as your daily doses have been stable for at least 28 days.

How often do I need to visit the hospital?

You will only need to visit the hospital clinic for your initial screening, at week 6, and at week 12. Other check-ups are conducted over the phone.

Does taking part cost anything?

No, the study medication and all trial-related health checks are provided free of charge through the NHS and Parkinson’s UK funding.

How to find out more

Olga Zubko

o.zubko@ucl.ac.uk +44 (0)20 3545 9073 Official trial record

Always speak to your GP or specialist before deciding to take part in a study.