A global expert review has identified a shingles vaccine and two existing drugs as leading candidates for repurposing against Alzheimer’s disease.
A new study has highlighted three approved medicines that could potentially be reused to treat or prevent Alzheimer’s disease.
The research, funded by Alzheimer’s Society and led by the University of Exeter, was recently published in Alzheimer’s Research and Therapy. The findings point to a shingles vaccine (Zostavax) as the most promising candidate for repurposing. Viagra (sildenafil) and riluzole, a drug currently used to treat motor neurone disease, also showed strong potential.
Dementia is the leading cause of death in the UK, affecting around one million people. About one in three people born today will develop dementia at some point in their lives, and there is still no cure.
Why existing medicines offer hope
Developing brand new drugs is a slow and costly process that can take 10 to 15 years and require billions of pounds, with no certainty of success. In contrast, repurposing medicines that are already approved for other conditions can dramatically shorten development timelines, reduce costs, and lower safety risks, making it an attractive strategy for tackling dementia.
The research also received support from the National Institute for Health and Care Research (NIHR), the Exeter Biomedical Research Centre, and the NIHR HealthTech Research Centre in Brain Health. As part of the project, an international panel of 21 experts in dementia, drawn from academia, hospitals, the pharmaceutical industry, and people affected by the condition, systematically reviewed 80 existing drugs. Their goal was to determine which medicines had the strongest potential to treat or prevent Alzheimer’s disease, which accounts for more than half of all dementia diagnoses.
Through multiple rounds of evaluation, the panel narrowed the list to a small number of candidates that target biological processes linked to Alzheimer’s and are known to be safe for use in older adults, laying the groundwork for future clinical trials.
Three candidates with different paths to impact
After several rounds of careful review, the panel reached a consensus on the three ‘priority candidates’ for further investigation. These drugs were selected as they all targeted relevant mechanisms involved in Alzheimer’s disease, showed promise in cell and animal studies of Alzheimer’s, and are known to be safe to use by older people.
- Shingles vaccine (Zostavax): Research points to a connection between shingles infection and dementia. Because immune system changes are known to influence Alzheimer’s disease, the vaccine’s effects on immune responses may help guard against some of these harmful changes.
- Sildenafil (Viagra): Studies indicate this drug can help protect nerve cells and lower the buildup of the tau protein in the brain. In mouse experiments, it also improved cognitive performance, an effect thought to result from increased blood flow to the brain.
- Riluzole: This medication is already used to treat motor neuron disease. Animal studies suggest it may improve cognition and reduce levels of tau, showing potential relevance for Alzheimer’s disease research.
The experts recommended that these drugs now be tested in clinical trials to understand their benefit for people with or at risk of Alzheimer’s disease.
Why the shingles vaccine stands out
Of these three treatments, the shingles vaccine was found to be the most promising, particularly as it requires a maximum of two doses and has a strong safety record. Previous studies show people who had the jab could be 16% less likely to develop dementia.
The lead researchers now hope to carry out a large clinical trial of this shingles vaccine in the UK, using the study to monitor participants involved. PROTECT is an online registry where, once a year, participants are asked to answer questionnaires about themselves, their lifestyle, and health, and can take part in brain health research.
Five other drugs were shortlisted but did not meet the criteria for the ‘priority candidates’ list. These included fingolimod (used in MS), vortioxetine (used to treat major depressive disorder), microlithium (used to treat depression), dasitinib (used for leukemia), and cytisine (used in anasthetics).
Repurposing as a long-term strategy
Dr. Anne Corbett, Professor of Dementia Research at the University of Exeter, said:“Beating dementia will take every avenue of research – from using what we already know, to discovering new drugs to treat and prevent the condition.
“Drug repurposing is a vital part of that mix, helping us turn today’s medicine for one condition, into tomorrow’s treatment for another.
“It’s important to stress that these drugs need further investigation before we will know whether they can be used to treat or prevent Alzheimer’s. We now need to see robust clinical trials to understand their true value and know for certain if they are effective to treat or prevent Alzheimer’s.”
Prof Fiona Carragher, Chief Policy and Research Officer at Alzheimer’s Society, said: “Dementia devastates lives, but we believe research will beat it.
“Years ago, we saw aspirin being repurposed from being a painkiller to helping people reduce their risk of heart attack or stroke. This is what we want to see in the field of dementia, and why we believe drug repurposing is one of the most exciting frontiers in dementia research.”
Reference: “Drug repurposing for Alzheimer’s disease: a Delphi consensus and stakeholder consultation” by Anne Corbett, Janet Sultana, Kate Stych, Roger Mills, Jeff L. Cummings, Gareth Williams, Zahinoor Ismail, Maria Soto-Martin, Jacobo Mintzer, Serge Gauthier, Nigel H. Greig, Wendy Noble, Richard Killick, Mitchell K. P. Lai, Carol Routledge, Frank Walsh, Howard Fillit, Dag Aarsland, Roger Lane, Kathryn Mills and Clive Ballard, 18 November 2025, Alzheimer’s Research & Therapy.
DOI: 10.1186/s13195-025-01895-4
This study was funded by Alzheimer’s Society UK (Grant Ref: 624).
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