Despite billions of pounds having been spent globally on clinical trials researching Alzheimer’s disease treatments, scientists are yet to find a cure. A new US study has identified a link between taking Sildenafil, the active ingredient in Viagra, and a reduced risk of Alzheimer’s disease. The research found sildenafil patients had a 69% reduced risk of developing Alzheimer’s, and that lab tests on nerve cells from people with Alzheimer’s supported the possibility of sildenafil in the treatment of the disease.[1]
Understanding Alzheimer’s Disease
Alzheimer’s disease (AD) is the most common form of dementia. Dementia is the general term used to describe a decline in mental ability severe enough to interfere with daily life, associated with a decline in memory, reasoning and other thinking skills, and can be caused by many conditions. Alzheimer’s is a specific brain disease accounting for between 60% and 80% of dementia cases, typically starting with trouble remembering new information, and often progressing to more severe symptoms including disorientation, behavioural changes, and trouble speaking, swallowing and walking.[2]
Why is Alzheimer’s So Difficult to Treat?
Alzheimer’s disease affects hundreds of millions of people worldwide, and the mission to find a cure for the disease is one that many of the biggest pharmaceutical companies and research projects have taken on with limited success. We know that patients with Alzheimer’s disease have plaques in the brain consisting of the protein beta-amyloid and tau tangles, but so far clinical trials of drugs that target these proteins have not been successful in altering the disease.[3] The underlying biology of the disease is not yet fully understood, neither is why Alzheimer’s progresses faster in some people compared to others. Additionally, the blood-brain barrier restricts pathogens and toxins from entering the brain, so administering a drug that can effectively reach the brain is yet another difficulty in the treatment of the disease.
How might Sildenafil help prevent Alzheimer’s?
Sildenafil was initially designed as a heart drug due to its ability to widen the blood vessels and improve blood flow. It was then discovered that it improved blood flow elsewhere in the body, including the penis, and has since proven an effective erectile dysfunction treatment alongside other PDE5 inhibitor medications like Tadalafil and Vardenafil. Scientists have been exploring the effect of sildenafil on vascular dementia, the second most common form of dementia characterised by reduced blood flow damaging the brain, and now it appears it may help Alzheimer’s as well.[4]
Researchers out of the Genomic Medicine Institute at the Cleveland Clinic, Ohio have recently published their findings, where they examined 1608 FDA-approved drugs and observed their interactions with the gene and protein clusters thought to be closely linked to Alzheimer’s disease. In preclinical models, sildenafil presented as the best drug candidate for Alzheimer’s, significantly improving cognition and memory.[5]
Then the authors reviewed the analyses of 7.23 million US insurance claims for prescriptions, and found that claimants who were prescribed sildenafil were 69% less likely to develop Alzheimer’s over the following 6 years compared to those not taking sildenafil.
Lastly, the researchers conducted lab experiments on nerve cells from individuals with Alzheimer’s and found that sildenafil decreased tau accumulation (a biomarker of the progress of the disease) and promoted the growth of new nerve projections.[6]
The Future of Treating Alzheimer’s
Experts commented that this study is an exciting advancement for Alzheimer’s research, especially since being able to repurpose an already-existing drug can speed up the drug discovery process and bring down the cost, edging us closer to finding a potentially life-changing treatment.
Dr Catherine Hall, Senior Lecturer in Psychology at the University of Sussex, suggests that since reduced brain blood flow is typical of early Alzheimer’ disease development, and that Sildenafil is a cardiovascular drug, Sildenafil may have a protective effect through promoting brain blood flow and stopping Alzheimer’s disease from developing.[7] Whether or not we should all be taking sildenafil for preventing the disease years before Alzheimer’s develops is still very much a theory, with randomised clinical trials needed before we can draw definitive conclusions about its suitability. Regarding the insurance claim review, it’s important to recognise that association does not imply causation, and there are several hidden variables that may contribute to the apparent reduced risk of developing Alzheimer’s that this study found. We know that socioeconomic factors like wealth are a risk factor for Alzheimer’s and also correlated with sildenafil usage, which may have influenced the findings. For women, the study did also not show statistically significant findings in those using sildenafil (for pulmonary hypertension) versus non-sildenafil takers in relation to the risk of Alzheimer’s.
For men already taking sildenafil to treat erectile dysfunction, this research offers a very positive first look at the possible benefits of the treatment in slowing a decline in cognitive performance associated, and opens the door to future research that can hopefully unlock the potential of sildenafil for treating or preventing Alzheimer’s disease.
Please note that ED medications are only licensed to treat erectile dysfunction. If you have concerns about Alzheimer’s, you should discuss this with your GP or doctor.