An international panel of dementia researchers identified the shingles vaccine Zostavax as the most promising existing drug that could be repurposed to prevent or treat Alzheimer's disease, according to a study published November 17, 2025, in Alzheimer's Research and Therapy.
The University of Exeter-led research, funded by Alzheimer's Society, examined 80 existing medications and reached consensus on three priority candidates for further investigation, including the shingles vaccine, sildenafil, commonly known as Viagra, and riluzole, a drug used to treat motor neurone disease.
Twenty-one dementia experts from universities, hospitals, and the pharmaceutical industry, along with people affected by dementia, conducted the review to identify drugs with the greatest potential to treat or prevent Alzheimer's, which accounts for more than half of all diagnosed dementia cases.
The panel selected drugs based on their targeting of relevant Alzheimer's mechanisms, promise in cell and animal studies, and safety profiles in older adults, prioritizing medications that could reach patients faster than developing entirely new treatments.
How Did Researchers Select Zostavax From 80 Medications
The research team used a Delphi consensus methodology, systematically evaluating 80 candidate drugs across multiple criteria, including biological plausibility, preclinical evidence, and practical feasibility for large-scale trials.
The shingles vaccine emerged as the top candidate, particularly because it requires a maximum of two doses and has a strong safety record established through decades of use in older populations.
Dr. Anne Corbett, Professor of Dementia Research at the University of Exeter, emphasized that drug repurposing is a vital part of the treatment development mix, helping researchers turn today's medicine for one condition into tomorrow's treatment for another.
The expert panel included neurologists, geriatricians, pharmacologists, and pharmaceutical industry representatives who individually scored each candidate drug before group discussions resolved disagreements and established final rankings.
Stakeholder input from people living with dementia and their caregivers ensured that practical considerations such as administration route, dosing frequency, and side effect profiles influenced the selection process.
The collaborative approach balanced scientific rigor with real-world feasibility, identifying drugs most likely to succeed in large clinical trials and eventual clinical adoption.
Did you know?
Drug repurposing can accelerate treatment development from 10 to 15 years down to just a few years because existing medications already have established safety profiles, manufacturing processes, and regulatory approval pathways, potentially saving billions of pounds in development costs.
What Evidence Links Shingles Vaccine to Dementia Prevention
Previous observational studies showed people who received the shingles jab could be 16 percent less likely to develop dementia compared to unvaccinated individuals of similar age and health status.
More recent research published in Nature in April 2025 found that the shingles vaccine reduced dementia diagnoses by 20 percent over seven years in a study of more than 280,000 older adults in Wales.
The Welsh study analyzed health records of adults born between September 1925 and September 1942 who were registered with primary healthcare providers, comparing dementia rates between those who received Zostavax and demographically matched controls.
Research suggests a link between the varicella zoster virus that causes shingles and dementia, with the vaccine potentially helping the immune system protect against changes seen in Alzheimer's disease.
Changes to the immune system are known to play a role in Alzheimer's, and the vaccine interacts with the immune system in ways that could help to protect against some of these changes, according to study documentation.
Scientists hypothesize that chronic viral infections may trigger inflammatory processes that contribute to neurodegeneration, and vaccination could interrupt these pathological cascades before irreversible brain damage occurs.
Which Other Drugs Show Promise for Alzheimer's Treatment
Sildenafil, the active ingredient in Viagra, originally developed to treat erectile dysfunction and pulmonary hypertension, ranked as the second most promising repurposing candidate.
Previous computational studies analyzing insurance claims data found that sildenafil prescriptions were associated with reduced Alzheimer's diagnosis rates, though the biological mechanisms remain under investigation.
Researchers theorize that sildenafil's effects on blood vessel function and cerebral blood flow may contribute to neuroprotection, as vascular health plays a crucial role in cognitive function and dementia risk.
Riluzole, currently approved for treating amyotrophic lateral sclerosis or motor neurone disease, emerged as the third priority candidate based on its neuroprotective properties and ability to modulate glutamate signaling in the brain.
The drug has demonstrated safety in long-term use for neurodegenerative conditions and possesses mechanisms of action that could address multiple pathological features of Alzheimer's disease, including excitotoxicity and oxidative stress.
The expert panel noted that riluzole's existing approval for neurological conditions streamlines the regulatory pathway for dementia trials compared to completely novel compounds.
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Why Does Drug Repurposing Matter for Dementia Research
Prof. Fiona Carragher, Chief Policy and Research Officer at Alzheimer's Society, noted that developing new drugs from scratch can take 10 to 15 years and cost billions of pounds, with no guarantee they will work.
Years ago, researchers saw aspirin being repurposed from being a painkiller to helping people reduce their risk of heart attack or stroke, and this is what the dementia field wants to see replicated.
Drug repurposing represents one of the most exciting frontiers in dementia research because it leverages existing safety data, manufacturing infrastructure, and clinical experience to accelerate treatment availability.
The economic advantages of repurposing extend beyond development costs to include faster regulatory approval processes, established supply chains, and physician familiarity with prescribing practices.
With no new treatments for dementia approved in over 15 years despite massive pharmaceutical investment, repurposing offers pragmatic alternatives that could reach patients within years rather than decades.
Alzheimer's Society has made drug repurposing a strategic priority, directing research funding toward identifying and validating existing medications that show promise for preventing or slowing cognitive decline in aging populations.
What Clinical Trials Will Test the Shingles Vaccine Next
Lead researchers now hope to carry out a large clinical trial of the shingles vaccine in the United Kingdom using PROTECT, an online registry where participants answer annual questionnaires about their lifestyle and health.
The PROTECT study, a collaborative project between the University of Exeter and King's College London, currently includes 25,000 participants over age 50 who complete validated neuropsychological tests and health assessments from their homes.
This established infrastructure allows rapid enrollment and cost-effective data collection compared to traditional clinic-based trials.
The research was part-funded by the National Institute for Health and Care Research Exeter Biomedical Research Centre and NIHR HealthTech Research Centre in Brain Health, signaling institutional commitment to advancing the work.
Dr. Anne Corbett emphasized the importance of further investigation before clinical recommendations, stating that it is important to stress that these drugs need further investigation before researchers will know whether they can be used to treat or prevent Alzheimer's.
The planned trial will likely span several years and recruit thousands of participants to generate definitive evidence about whether shingles vaccination can meaningfully reduce dementia risk in carefully controlled conditions with rigorous outcome measurement.
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