Parkinson's disease: Common cough syrup revealed to slow down cognitive decline and dementia

Parkinson's disease (PD) is a progressive and complex neurodegenerative disorder that affects movement. It is narked not only by motor symptoms – such as tremors, stiffness, and bradykinesia – but also by cognitive decline . PD is also characterized by the degeneration and death of nerve cells in the brain that produce dopamine, a chemical messenger crucial for smooth and coordinated muscle movements. This loss of dopamine leads to a variety of motor and non-motor symptoms. Moreover, up to half of people with PD develop Parkinson’s disease dementia (PDD) within a decade, with symptoms ranging from memory loss and confusion to hallucinations and mood disturbances.

Recently, a groundbreaking phase 2 clinical trial has revealed that a common cough medicine can stabilize psychiatric symptoms and potentially slow cognitive decline in PDD patients.

Read on to know more.

The recent discovery

According to a clinical trial, Ambroxol , a common cough medicine (used in Europe), has shown promise in slowing cognitive decline in people with Parkinson’s disease dementia.


A 12-month study conducted by researchers at Lawson Research Institute found that Ambroxol helped stabilise psychiatric symptoms, improved cognitive function, and protected against brain damage in genetically at-risk participants.

The study published in JAMA Neurology compared the outcome of the expectorant Ambroxol with a placebo among participants with Parkinson’s disease dementia.

While primary and secondary outcomes were similar, participants on the placebo experienced worsening neuropsychiatric symptoms compared to symptoms remaining the same in the intervention group.

The results also showed a possible improvement in cognitive symptoms for people with variants of a particular gene.


Understanding Parkinson’s Dementia


Parkinson’s disease dementia is a progressive condition superimposed on the classic movement symptoms of PD. It typically manifests in the later stages of the disease and includes cognitive impairment – memory lapses, executive dysfunction, visual hallucinations, and mood disturbances like depression or apathy.

Approximately 153,000 people in the UK live with PD. There is currently no cure for PDD, but patients can take medications called cholinesterase inhibitors to help manage symptoms. Existing treatments, such as cholinesterase inhibitors (e.g., rivastigmine, donepezil) and memantine, may provide some symptomatic relief but fail to halt or alter the underlying neurodegeneration.


Ambroxol: From cough syrup to neuroprotection


Ambroxol has been widely used in Europe for decades as a mucoactive agent – it helps clear phlegm and has an excellent safety profile. Its potential in neurodegenerative disease stems from its ability to enhance glucocerebrosidase (GCase) activity, a key enzyme encoded by the GBA1 gene. Reduced GCase activity leads to the build-up of alpha-synuclein, a hallmark of PD and PDD. By enhancing GCase, Ambroxol may promote the clearance of pathological proteins and reduce brain cell damage.


Key findings from the phase 2 trial

Researchers at Lawson Research Institute conducted a 12-month, randomized, placebo-controlled trial in 55 PDD patients, administering high-dose Ambroxol (525–1,050 mg/day). The major outcomes included:


Symptom stabilization: Placebo participants experienced significant worsening in neuropsychiatric measures, while those on Ambroxol remained stable.

Brain injury marker (GFAP): Serum GFAP – a biomarker of neuronal damage – increased in the placebo group but remained stable with Ambroxol, implying neuroprotective action.

Cognitive improvement in high-risk individuals: Patients harboring GBA1 risk variants exhibited noticeable cognitive gains.

Safety and tolerance: Ambroxol was generally well-tolerated, with no serious adverse effects noted.

One detailed report noted that high-dose Ambroxol recipients showed improved Montreal Cognitive Assessment (MoCA) scores by approximately 2 points, while placebo subjects declined.


Limitations and the way ahead

While findings are promising, they come from a small, single-center Phase 2 trial with limited diversity and may not be fully statistically conclusive. Certain dose‑response relationships remain unclear, and the subset of GBA1 carriers was small – about eight participants. Researchers are planning larger Phase 3 clinical trials in 2025 to specifically evaluate cognitive outcomes and determine optimal dosing strategies.


The parting thought

Ambroxol’s success could inspire wider interest in repurposing safe, existing medications for neurodegenerative disorders. It also supports the hypothesis that enhancing GCase activity may combat alpha-synuclein pathologies – a concept applicable to Parkinson’s, dementia with Lewy bodies, and potentially Gaucher disease.

Moreover, this study draws attention to the value of targeted precision medicine – showing particular promise in patients with genetic risk factors (e.g., GBA1 variants). This could pave the way for more personalized neurotherapy approaches