Ambroxol, a drug commonly used in cough medicines in Europe, is now being investigated as a potential treatment for Parkinson’s. Unlike existing therapies that only manage symptoms, ambroxol is one of the few candidates in late-stage clinical trials that could help slow or change the course of the condition. Early findings are encouraging and mark an important shift in Parkinson’s research. 

Overview 

What is ambroxol? 
Ambroxol is widely used in Europe to thin mucus in the respiratory system, but it is not approved in Canada or the U.S. Researchers became interested in the drug after finding evidence that it may enhance the function of GCase, an enzyme that helps clear harmful substances from brain cells. Low levels of GCase are potentially linked to Parkinson’s. 

Why is ambroxol being studied for Parkinson’s? 
Problems with GCase can lead to the buildup of harmful proteins like alpha-synuclein, which damage dopamine-producing neurons. By improving GCase activity, ambroxol may be able to reduce or stop this buildup and protect brain cells. 

Clinical trials: Where are we now? 

Which clinical trial phase is ambroxol currently in? 

Ambroxol is currently being studied in both phase II and phase III trials: 

– Phase II studies in Ontario and the UK have shown that ambroxol is safe and can affect GCase activity in the brain. 
– A phase III trial in the UK is underway to test whether ambroxol can slow or stop the progression of Parkinson’s. 
– A phase II study in Ontario, completed in June of 2025, found ambroxol was safe, improved GCase function, and showed possible benefits for psychiatric and cognitive symptoms. 

There are currently four disease-modifying therapies in phase III trials for Parkinson’s. Ambroxol and lactobacillus acidophilus are existing drugs being repurposed, while prasinezumab and bemdaneprocel were specifically developed for Parkinson’s. 

How does it work? 

Ambroxol supports the function of an enzyme in the brain called glucocerebrosidase (GCase). This enzyme helps cells clear out waste and keep themselves healthy. When GCase levels are too low, harmful proteins such as alpha-synuclein can start to build up. Over time, these proteins clump together into structures called Lewy bodies, which are toxic to brain cells. These clumps especially damage dopamine-producing neurons – the very cells that are lost in Parkinson’s – and this drives the progression of symptoms. 

Why target GCase and alpha-synuclein? 

By increasing GCase activity, ambroxol may help the brain clear out more of this waste and reduce the buildup of harmful protein clumps. Protecting dopamine-producing neurons in this way could slow the loss of these vital cells and change the course of Parkinson’s rather than only treating symptoms. Early studies have shown that ambroxol can cross into the brain and boost GCase activity, which makes it one of the more promising disease-modifying candidates being investigated today. 

Future outlook 

Phase III trials take time, and results from the UK study are expected in the coming years. As of April 1, 2025, the first participant was dosed in the UK trial. By June 30, 2025, the Ontario phase II trial concluded, confirming ambroxol’s safety and showing it boosted GCase activity with early potential signs of symptom benefit. 

Ambroxol may be especially effective for people with GBA1 gene mutations – the most common genetic risk factor for Parkinson’s. However, researchers are also studying its effects in people without genetic links. 

Even if ambroxol does not ultimately prove to be disease-modifying, its trials will still provide valuable data on Parkinson’s biology and inform the design of future therapies. 

More to know 

Disease-modifying vs. symptomatic treatments: 
Disease-modifying therapies target the underlying biology of Parkinson’s to slow or change its progression, while symptomatic therapies only manage symptoms. 

Other GCase-targeting drugs: 
Several are under investigation, but ambroxol is the furthest along in clinical trials.