Cough Syrup Slows Brain Damage in Parkinson’s Dementia, Study Finds

A decades-old cough medicine, Ambroxol, could be on the verge of a dramatic second act—not for sore throats, but for protecting the brain.

In a year-long clinical trial, researchers gave Ambroxol to people with Parkinson’s-related dementia and found that it reached the brain, slowed signs of cell damage, and helped stabilize memory and psychiatric symptoms. Participants with high-risk genes even showed cognitive improvement. Meanwhile, those on placebo declined. Safe, well-tolerated, and already approved in Europe for respiratory issues, Ambroxol may be a long-overlooked ally in the fight against neurodegeneration.

Dementia Crisis & Treatment Gap

Dementia remains one of the most pressing health challenges today, with no safe and affordable options to slow its progression. But a familiar medication may offer a surprising new lead.

Researchers at the Lawson Health Research Institute, part of St. Joseph’s Health Care London, are studying Ambroxol, a cough medicine that has been used safely for decades in Europe, to see if it can slow the progression of dementia in people with Parkinson’s disease.

A new clinical trial, published in JAMA Neurology, followed 55 participants with Parkinson’s disease dementia (PDD) for 12 months. The team tracked changes in memory, psychiatric symptoms, and levels of GFAP, a blood marker linked to brain cell damage. Parkinson’s-related dementia affects nearly half of those diagnosed with the disease within 10 years, causing memory loss, confusion, mood changes, and hallucinations. These symptoms take a significant toll on patients, their families, and the healthcare system.

Ambroxol Clinical Trial Insights

Led by cognitive neurologist Dr. Stephen Pasternak, the study divided participants into two groups. One group received daily doses of Ambroxol, while the other was given a placebo. “Our goal was to change the course of Parkinson’s dementia,” says Pasternak. “This early trial offers hope and provides a strong foundation for larger studies.”

Key findings from the clinical trial include:

• Ambroxol was safe, well-tolerated, and reached therapeutic levels in the brain
• Psychiatric symptoms worsened in the placebo group but remained stable in those taking Ambroxol.
• Participants with high-risk GBA1 gene variants showed improved cognitive performance on Ambroxol
• A marker of brain cell damage (GFAP) increased in the placebo group but stayed stable with Ambroxol, suggesting potential brain protection.

Although Ambroxol is approved in Europe for treating respiratory conditions and has a long-standing safety record, including use at high doses and during pregnancy, it is not approved for any use in Canada or the U.S.

Promising Neuroprotective Signals

“Current therapies for Parkinson’s disease and dementia address symptoms but do not stop the underlying disease,” explains Pasternak. “These findings suggest Ambroxol may protect brain function, especially in those genetically at risk. It offers a promising new treatment avenue where few currently exist.”

Ambroxol supports a key enzyme called glucocerebrosidase (GCase), which is produced by the GBA1 gene. In people with Parkinson’s disease, GCase levels are often low. When this enzyme doesn’t work properly, waste builds up in brain cells, leading to damage. Pasternak learned about Ambroxol during a fellowship at The Hospital for Sick Children (SickKids) in Toronto, where it was identified as a treatment for Gaucher disease – a rare genetic disorder in children caused by a deficiency of GCase.

He is now applying that research to explore whether boosting GCase with Ambroxol could help protect the brain in Parkinson’s-related diseases. “This research is vital because Parkinson’s dementia profoundly affects patients and families,” says Pasternak. “If a drug like Ambroxol can help, it could offer real hope and improve lives.”

Reference: “Ambroxol as a Treatment for Parkinson Disease Dementia: A Randomized Clinical Trial” by Carolina R. A. Silveira, Kristy K. L. Coleman, Kathy Borron, Rommel G. Tirona, Charles A. Rupar, Guangyong Zou, Robert A. Hegele, Cheryl Wellington, Sophie Stukas, Elizabeth C. Finger, Robert Bartha, Sarah A. Morrow, Jennie L. Wells, Michael J. Borrie, Don Mahuran, Penny A. MacDonald, Mary E. Jenkins, Mandar S. Jog, George Dresser, Susan Fox, Richard Camicioli, Brian Feagan, Daniel A. Mendonça, Michael Mayich, Manas D. Sharma, Sachin K. Pandey and Stephen H. Pasternak, 30 June 2025, JAMA Neurology.
DOI: 10.1001/jamaneurol.2025.1687

Funded by the Weston Foundation, this study is an important step toward developing new treatments for Parkinson’s disease and other cognitive disorders, including dementia with Lewy bodies. Pasternak and his team plan to start a follow-up clinical trial focused specifically on cognition later this year.

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