Viagra may also reduce the risk of developing Alzheimer’s or dementia. While this link isn’t causative, the new research opens the door for clinical trials into efficacy.
Believe it or not, Pfizer’s drug Viagra was originally designed to treat cardiovascular problems. Early on in clinical trials, men taking the drug became nervous when nurses came into the room to check in on them. It became obvious that the drug was successful at increasing blood flow, though not where Pfizer intended. Thus, the story goes, researchers accidentally discovered that the active ingredient in Viagra, sildenafil, treats erectile dysfunction.
In an act of further serendipity, researchers have now discovered that Viagra is associated with a lower risk of developing Alzheimer’s or dementia. According to headlines from the New York Post, “Taking Viagra cuts the risk of Alzheimer’s by up to 69 percent.” Meanwhile, The Guardian proclaims: “Viagra could be used to treat Alzheimer’s disease, study finds.” Both of these headlines, however, are inflating and misrepresenting the new study’s findings.
The research, recently published in Nature Aging, investigated a dataset of 7.23 million individuals through data obtained from insurance claims. When controlling for age, sex, race, and disease comorbidities, the scientific team at the Cleveland Clinic’s Genomic Medicine Institute found that Viagra was associated with a 69-percent reduction in Alzheimer’s risk after a six-year follow-up.
People taking Viagra also showed a significant reduction in Alzheimer’s risk compared to people taking common blood-pressure-lowering or diabetes medications like losartan, metformin, diltiazem, and glimepiride.
However, when the data were stratified by sex, the reduction was only significant in males (see Supplementary Table 9) who are both more likely to be prescribed Viagra, and less likely to develop Alzheimer’s. This means that the majority of this risk reduction comes from the effect in males, while the results did not find a significant reduction in the risk for females who took Viagra, despite that females have a higher likelihood of developing dementia than males.
“Notably, we found that sildenafil use reduced the likelihood of Alzheimer’s in individuals with coronary artery disease, hypertension, and type 2 diabetes, all of which are comorbidities significantly associated with risk of the disease, as well as in those without,” Cleveland Clinic computational biologist Feixiong Cheng, a senior author of the study, said in a news release.
To identify Viagra, the researchers used a computational approach to look for drugs with the potential to impact pathways implicated in Alzheimer’s.
“We hypothesized that drugs targeting the molecular network intersection of amyloid and tau endophenotypes should have the greatest potential for success,” Cheng said, adding that Viagra also improved cognition and memory in animal models of Alzheimer’s disease.
Cheng’s group also tested the effects of sildenafil on cells in a dish to see whether it could reduce tau, a toxic protein that aggregates in tangles in brains with Alzheimer’s. However, Jack Auty, lecturer in the Medical Sciences at the University of Tasmania, noted in a reaction to the study that the drug was administered to these cells at a very high concentration, “around 100 times that achieved by taking the pill.”
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While studies with large datasets are able to find these strong links, they do not prove causation. The authors and other neuroscience researchers pointed towards limitations in claiming sildenafil as a preventative agent for Alzheimer’s.
Earlier this year, a class of blood pressure medications and a water-retention drug were found to reduce the risk of cognitive decline or Alzheimer’s. Viagra is by no means the first blood pressure drug associated with risk-reduction in Alzheimer’s.
“There are other possible explanations for these findings; for example, we know that brain changes start decades before dementia symptoms, and it is possible that these early Alzheimer’s changes reduce sex drive (thus people wouldn’t ask for a prescription for erectile dysfunction),” Tara Spires-Jones, deputy director of the centre for discovery brain sciences, University of Edinburgh, wrote of the study.
Because the study’s findings only establish an association between sildenafil use and reduced incidence of Alzheimer’s disease, rather than a proven link, Cheng said, his team is now planning a mechanistic trial and a phase II randomized clinical trial of sildenafil, in order to test causality and confirm the drug’s clinical benefits for Alzheimer’s patients.
