A University of Exeter-led study funded by Alzheimer’s Society has identified three already-approved medicines—the shingles vaccine Zostavax, sildenafil (Viagra) and riluzole—as top “priority” candidates to be tested in clinical trials for Alzheimer’s disease, after a structured review of 80 existing drugs by an international expert panel.
Researchers led by the University of Exeter, with support from Alzheimer’s Society and the UK’s National Institute for Health and Care Research (NIHR) and related Exeter NIHR centres, have published a study in Alzheimer’s Research & Therapy evaluating whether existing medicines could be repurposed to help treat or prevent Alzheimer’s disease.
The project used a Delphi-style consensus process and stakeholder consultation. A panel of 21 dementia specialists from universities, hospitals and the pharmaceutical industry, together with people affected by dementia, reviewed evidence on 80 approved medications. The group assessed candidates based on whether they could plausibly influence biological processes linked to Alzheimer’s, whether there was supportive evidence from cell and animal studies, and whether the drugs are considered suitable for older adults.
After multiple rounds of review, the panel selected three “priority candidates” for further investigation:
Herpes zoster (shingles) vaccine (Zostavax): The panel cited growing evidence linking herpes zoster vaccination with lower rates of dementia diagnoses in observational and quasi-experimental studies. The Alzheimer’s Research & Therapy paper notes a systematic review estimating about a 16% reduction in incident dementia among vaccinated people across several epidemiological studies. The vaccine also stood out to the panel as a pragmatic candidate because it typically requires no more than two doses and has a long safety record.
Sildenafil (Viagra): The study highlighted laboratory and animal evidence suggesting sildenafil could affect pathways relevant to Alzheimer’s, including effects on tau-related biology and neuronal health, alongside a mechanistic rationale tied to its vascular and cellular signaling actions.
Riluzole: Best known as a medicine used to prolong survival in amyotrophic lateral sclerosis (ALS), riluzole was prioritized based largely on non-clinical evidence, including animal studies reporting cognitive effects and tau-related changes, as well as limited early clinical signals in Alzheimer’s populations.
Five other drugs were shortlisted but were not named priority candidates: fingolimod (multiple sclerosis), vortioxetine (major depressive disorder), microlithium (described in the Exeter materials as being used for depression), dasatinib (leukaemia), and cytisine (described in the Exeter materials as being used in anaesthetics).
The authors and external stakeholders emphasized that the findings do not show these medicines prevent or treat Alzheimer’s, and that robust clinical trials are needed to determine whether any benefit is real and clinically meaningful.
Dementia is the leading cause of death in the UK and affects around one million people, the researchers noted, arguing that repurposing established medicines could shorten timelines compared with developing new drugs from scratch—often estimated at 10 to 15 years and requiring substantial investment.
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… 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.”
Prof. Fiona Carragher, Chief Policy and Research Officer at Alzheimer’s Society, said drug repurposing could speed progress in dementia research, comparing the approach to earlier examples of medicines being adopted for new clinical purposes.
Among the proposals discussed is a UK clinical trial focused on shingles vaccination, with researchers aiming to use PROTECT, an online registry in which volunteers complete annual questionnaires about their health and lifestyle and take part in brain health research.
