By Andrew Gregory

Viagra could be a useful treatment against Alzheimer’s disease, according to a US study.

Alzheimer’s disease, the most common form of age-related dementia, affects hundreds of millions of people worldwide. Despite mounting numbers of cases, however, there is currently no effective treatment.

Using a large gene-mapping network, researchers at the Cleveland Clinic integrated genetic and other data to determine which of more than 1,600 Food and Drug Administration-approved drugs could be an effective treatment for Alzheimer’s disease. They gave higher scores to drugs that target both amyloid and tau – two hallmarks of Alzheimer’s – compared with drugs that targeted just one or the other.

“Sildenafil, which has been shown to significantly improve cognition and memory in preclinical models, presented as the best drug candidate,” said Dr Feixiong Cheng, the study lead. Viagra is the brand name of sildenafil.

Researchers then used a database of claims from more than 7 million people in the US to examine the relationship between sildenafil and Alzheimer’s disease outcomes by comparing sildenafil users to non-users.

They found sildenafil users were 69% less likely to develop Alzheimer’s disease than non-sildenafil users after six years of follow-up. To further explore the drug’s potential effect on Alzheimer’s disease, researchers developed a lab model that showed that sildenafil increased brain cell growth and targeted tau proteins, offering insights into how it might influence disease-related brain changes.

Cheng cautioned that the study does not demonstrate a causal relationship between sildenafil and Alzhemer’s disease. Randomised clinical trials involving both sexes with a placebo control were needed to determine sildenafil’s efficacy, he said.

Dr Ivan Koychev, a senior clinical researcher at the University of Oxford, who was not involved in the study, said it was “an exciting development” because “it points to a specific drug which may offer a new approach to treating the condition”.

Prof Tara Spires-Jones, deputy director of the Centre for Discovery Brain Sciences at the University of Edinburgh, said there were several important limitations to consider. “While these data are interesting scientifically, based on this study, I would not rush out to start taking sildenafil as a prevention for Alzheimer’s disease.”

Dr Susan Kohlhaas, director of research at Alzheimer’s Research UK, said: “Being able to repurpose a drug already licensed for other health conditions could help speed up the drug discovery process and bring about life-changing dementia treatments sooner.

“Importantly, this research doesn’t prove that sildenafil is responsible for reducing dementia risk, or that it slows or stops the disease. The only way to test this would be in a large-scale clinical trial measuring sildenafil effect against the usual standard of care.”