Anti-Nausea Drug Used for Chemotherapy Could Treat Parkinson’s Hallucinations

Older adult holding pills in her hand.

Guido Mieth / Getty Images

Key Takeaways

  • Researchers are recruiting Parkinson's patients who struggle with hallucinations for a new clinical trial.
  • The trial will test whether the anti-nausea medication ondansetron can help stop hallucinations for patients.
  • The drug is most commonly used for cancer patients.

Researchers are investigating whether an anti-nausea drug commonly used for chemotherapy patients can help stop hallucinations in people with Parkinson’s disease. The medication, ondansetron, also known as Zofran, is being studied as part of a trial conducted by researchers at the University College London and non-profit organization Parkinson’s U.K.

Researchers are actively searching for 216 people diagnosed with Parkinson’s who experience hallucinations related to the disease at least once a week. Patients must also be on a stable dose of medication to control their disease for 28 days before starting the trial. Once a patient is approved to take part in the trial, they will be randomly assigned to receive either ondansetron or a placebo via mail.

The Trial of Ondansetron as a Parkinson's Hallucination Treatment (TOPHAT) is a $1.3 million phase 2 clinical trial. To minimize risk due to COVID-19, researchers plan to conduct the majority of the study via video or telephone consultations. 

“If this research shows that ondansetron is safe and effective, it could be made available to people with Parkinson's…without the need for further studies,” Parkinson’s U.K. said in a press release. “This could mean a vital new treatment in just a few years.”

What This Means For You

Ondansetron is an anti-nausea medication often used by cancer patients. However, it may eventually be used to treat hallucinations in patients with Parkinson’s disease if proven to be effective.

Parkinson’s Disease and Hallucinations

Parkinson's disease is a brain disorder that leads to shaking, stiffness, and difficulty with walking, balance, and coordination, according to the National Institute on Aging (NIA). It's a progressive disease, meaning, symptoms get worse with time. As the disease progresses, people may experience mental and behavioral changes, sleep issues, depression, memory problems, and fatigue.

Hallucinations in Parkinson’s disease, also known as Parkinson’s disease psychosis (PDP), occurs in between 20% to 40% of people with the disease, the Parkinson’s Foundation says. As the disease progresses over time, that number increases.

About 60,000 people in the U.S. are diagnosed with Parkinson’s disease each year, according to the Parkinson’s Foundation.

Why do hallucinations happen in Parkinson’s patients? It’s due to the disease’s impact on the brain. “There's a delicate balance between different chemicals in the brain that help it to make sense of all the visual information it is receiving,” Suzanne Reeves, PhD, lead researcher of the new study and professor of Old Age Psychiatry and Psychopharmacology at University College London, tells Verywell. “Parkinson's disrupts that delicate balance, so the brain reaches the wrong conclusion about the visual information it is getting—hence the hallucinations.”

The hallucinations can include temporary delirium that can be resolved by adjusting medication and isolated minor hallucinations, as well as illusions, where people misinterpret things that they see. The main forms of hallucinations a person with Parkinson’s disease may experience are:

  • Visual: Often includes seeing animals or people that are not present. This is the most common type linked to Parkinson’s disease.
  • Auditory: Hearing voices or sounds that are not real. This is less common with Parkinson’s disease.
  • Olfactory: Smelling an odor that is not related to an actual source. This is rare in Parkinson’s disease.
  • Tactile: Feeling something imaginary, like bugs crawling on your skin. This is also rare in Parkinson’s disease.
  • Gustatory: Sensing a bitter or abnormal taste in your mouth that has no source. This is rare in Parkinson’s disease.

“While not everyone gets hallucinations, enough Parkinson’s patients have this problem that it is important to screen for,” Amit Sachdev, MD, medical director in the division of neuromuscular medicine at Michigan State University, tells Verywell.

How an Anti-Nausea Drug May Help

“There are limited medication options” to treat hallucinations in Parkinson’s patients, David A. Merrill, MD, PhD, director of the Pacific Neuroscience Institute’s Pacific Brain Health Center at Providence Saint John’s Health Center in California, tells Verywell. Currently, the drug Nuplazid is the only FDA-approved medication in the U.S. to treat hallucinations in Parkinson’s patients. “The way it works is it binds to serotonin receptors to try to stop the hallucinations,” Merrill says.

But current medications to treat Parkinson’s hallucinations “can cause significant side effects including sleepiness, falls, and a worsening of Parkinson’s symptoms, such as tremor,” Reeves says.

There is some precedence for using ondansetron to treat Parkinson’s hallucinations. “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,” Arthur Roach, PhD, director of research at Parkinson's U.K., tells Verywell. “At the time, the high cost of ondansetron prevented further studies but it is now affordable. If this research study finds that ondansetron is effective and tolerable as a treatment for visual hallucinations, we could see clinicians prescribing an inexpensive drug with fewer side effects to people with Parkinson’s.”

Like Nuplazid, ondansetron targets serotonin receptors, Sachdev explains. “Ondansetron acts in a targeted way that seems very helpful for nausea but it is not well studied for hallucinations,” he says.

There is a long way to go before this medication can safely be used to treat Parkinson’s patients with hallucinations. “At this point, I would choose better-studied medications first,” Sachdev says.

The new trial won’t start until at least November 2022, which is when researchers plan to stop inviting participants to join.

Was this page helpful?
5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Parkinson's UK. TOPHAT - Trial of ondansetron as a Parkinson's hallucination treatment.

  2. Parkinson's UK. Could an anti-sickness drug treat hallucinations in Parkinson's?

  3. National Institute on Aging. Parkinson's disease.

  4. Parkinson's Foundation. Hallucinations/delusions.

  5. Parkinson's Foundation. Statistics.