UCL Queen Square Institute of Neurology


Cancer anti-sickness drug offers hope for hallucinations in Parkinson’s

30 October 2020

A world-first double-blind clinical trial led by UCL researchers will investigate if a powerful drug used to treat nausea in chemotherapy patients could alleviate hallucinations in people with Parkinson’s.


Parkinson’s UK is partnering with UCL and investing £1 million in a pioneering phase II clinical trial to explore if the drug ondansetron is safe and effective against hallucinations.

There are currently 145,000 people living with Parkinson’s in the UK and 75% of them will experience visual hallucinations at some point.

The trial comes at a crucial time as a survey carried out by the charity found that one in 10 people with Parkinson’s reported an increase in hallucinations during lockdown, which led to an increase in calls to their helpline.

Lead Researcher Professor Suzanne Reeves (UCL Psychiatry) said: “Visual hallucinations pose a particular challenge in Parkinson’s as the very treatments for motor symptoms in Parkinson’s can also trigger and worsen this distressing symptom. Finding treatments for hallucinations that are both effective and safe is an area of great unmet need.

“Ondansetron influences visual processing in the brain and its potential for treating visual hallucinations in Parkinson’s was first identified in small studies in the early 1990s.

“This trial will enable us to find out if ondansetron is effective and safe as a treatment and if it is, we could see clinicians prescribing an inexpensive drug with fewer side effects to people with Parkinson’s throughout the UK.”

Treating hallucinations is one of the most challenging aspects in people with Parkinson’s and it can have a big effect on their quality of life. It can be extremely distressing for carers as well as people with Parkinson’s, putting stress on relationships. The only medications available to treat it today are anti-psychotic drugs which can worsen Parkinson's symptoms and potentially cause serious side effects.

The 12-week, double-blind, placebo-controlled trial is set to recruit 216 people over two years in 20-25 NHS clinics across the UK. Patients will be randomised to receive either drug or placebo tablets, to take at home for 12 weeks. To accommodate social distancing, researchers will conduct the majority of the study via video or telephone consultations, with face-to-face assessments limited to only three for essential blood tests or ECGs. Visual and other types of hallucinations, as well as delusions (false beliefs), will be assessed after six and 12 weeks of treatment, along with Parkinson’s related motor and non-motor symptoms.

Dr Arthur Roach, Director of Research at Parkinson's UK said: “It’s vital we find better treatments for people with Parkinson's who have seen their hallucinations worsen at home and ondansetron offers much hope for them and their families. If successful, positive results from the trial could see this drug, which is already used in the NHS, quickly repurposed to become an available treatment in Parkinson’s.

“With the support of Parkinson’s UK, UCL has been rapidly adapting the research during the pandemic, to enable us to drive forward and launch this promising trial, which marks another milestone in our thriving Parkinson’s Virtual Biotech programme.”

Dr Rimona Weil (UCL Queen Square Institute of Neurology), who will be leading the clinical work at UCLH, said: We are excited to be carrying out this trial at UCLH. Visual hallucinations can be distressing in Parkinson’s disease and we currently lack effective and accessible treatments. This trial offers a new chance to treat hallucinations which can often be so challenging for patients and their families.”

Michelle Ellis, 54, from Ashby-de-la-Zouch, Leicestershire, was diagnosed with Parkinson’s at the age of 46 in 2012. She experienced her first hallucination four years later.

“One evening, returning from visiting a friend, we pulled into a service station. My husband was driving and my seven-year-old granddaughter, Amy, was in the car. I turned around to see if she was asleep, and I saw someone sitting next to her. I told my husband, ‘Stop the car, someone is in the back with Amy.’ I was convinced. But my husband promised me nobody was there. I felt very frightened. My hallucinations always featured random people who were walking around the house and they were happening daily so it was quite terrifying.”

Michelle saw a specialist nurse two years ago who lowered her Madopar medication and the hallucinations stopped. They were few and far between however, in the past few months they have become more frequent. Michelle continues to see movement and shadows out of the corner of her eyes and is worried about what this means for the future.

“My hallucinations never really went away and have become worse. I am worried because they have started to increase in the past few months and I want them to settle down. I tend to dwell on them when I am having a bad day with my Parkinson’s symptoms. It’s very important to have a drug that focuses on treating hallucinations on their own.”




  • Pills. Source: Fabio Hofnik on Flickr (CC BY-ND 2.0)