Viagra (sildenafil), which is commonly used to treat erectile dysfunction, could be a useful treatment against Alzheimer’s disease, according to a new study published in the journal Nature Aging.

The study, led by the Genomic Medicine Institute at the Cleveland Clinic, used a large gene-mapping network to determine which FDA-approved drugs could prove to be an effective treatment.

After analysing the findings, the researchers found that sildenafil presented as the best drug candidate, according to Dr Feixiong Cheng, the study lead.

Men taking sildenafil were 69% less likely to develop Alzheimer’s disease

The team then analysed a database of seven million patients and found that men who were on the drug were 69% less likely to develop Alzheimer’s disease over a six-year follow-up period compared with non-sildenafil users.

The association remained statistically significant after accounting for other factors that influence Alzheimer’s risk, including other medical conditions such as coronary artery disease, type 2 diabetes and mild cognitive impairment.

The drug was also tested in a lab on nerve cells from individuals with Alzheimer’s to prove it had an affect on the underlying mechanism of the disease.

The researchers found that sildenafil targeted two hallmarks of Alzheimer’s – plaques of a protein called amyloid as well as tangles of a protein called tau. The results therefore supported the idea that sildenafil may treat Alzheimer’s disease.

Clinical trials now needed to establish a cause

While the study is observational and cannot demonstrate a causal relationship, the researchers remain hopeful that sildenafil could be used as a potential treatment for Alzheimer’s disease.

However, the authors say large-scale clinical trials will need to be carried to prove this relationship, as they conclude: “Taken together, the association between sildenafil usage and decreased incidence of [Alzheimer’s disease] does not establish causality or its direction, and our results, therefore, warrant rigorous clinical trial testing of the treatment efficacy of sildenafil in patients with [Alzheimer’s disease], inclusive of both sexes and controlled by placebo.”