Recent studies on the effects of sildenafil (Viagra) on Alzheimer’s risk show it may offer some prevention — and potentially a treatment — for the disease. But more research is needed.
Sildenafil is a vasodilator, meaning it expands your blood vessels to ease blood flow. Doctors prescribe it for erectile dysfunction (problems getting and keeping an erection), as well as pulmonary arterial hypertension (as the drug Revatio).
Researchers are exploring using sildenafil to treat Alzheimer’s disease. However, there haven’t been any clinical trials to test the drug for this purpose, and the medical community hasn’t made any recommendations yet.
Viagra and Tau Levels: What It Means
Alzheimer's is defined by two proteins: amyloid and tau. In the Alzheimer’s brain, abnormal levels of specific amyloids clump together, form plaques, and disrupt normal cell function. Abnormal tau levels cause “tangles” inside brain cells (neurons).
In healthy neurons, tau attaches to stabilizing structures called microtubules, which help guide nutrients and molecules from inside the cell outward. When tangles happen, it’s because chemical changes cause tau to detach from the microtubules and stick to other tau molecules. This forms “threads” that, over time, tangle up and block this transport system.
When your brain cells can’t get nutrients and molecules out like they should, they can’t communicate well, and they also start dying.
Based on emerging evidence, researchers believe Alzheimer’s-related brain changes happen because of a complex interaction between abnormal tau and beta-amyloid proteins and several other factors. As beta-amyloid clumps form plaques, tau starts to spread quickly through the brain.
“Tau has a clear relationship between symptoms and spatial location in the brain,” says Kyan Younes, MD, clinical assistant professor of neurology at Stanford University School of Medicine. “Wherever tau is, you expect symptoms. So if it's in the memory area, you expect memory problems.”
A 2024 study in Journal of Alzheimer’s Disease used computational models, insurance claims data, and observations from brain cells in Alzheimer’s patients to look at whether taking sildenafil had an effect on toxic tau levels in their brains. They found that those on the drug had lowered levels. This led scientists to consider the possibility that Viagra may work as one form of Alzheimer’s treatment.
Can Viagra Be Used to Treat Alzheimer’s?
An important thing to remember about the promising study in the Journal of Alzheimer’s Disease is that it’s more a study for healthy people rather than data that applies to people with Alzheimer’s disease.
Instead of noting how it acts on the disease, the study looked at exposure to Viagra before a diagnosis and how that seemed to reduce the chances of getting Alzheimer’s in the future.
In addition, Alzheimer’s therapy is similar to cancer or HIV therapy — one medication is not enough; you need multiple approaches. Even if researchers do clinical trials on Viagra and find out it may treat Alzheimer’s, it’s not going to be a cure-all, says Younes.
“It might be something that can be helpful eventually if it's positive, but I don't think it's going to be a magical pill,” he says.
“You need to target different mechanisms [including] the amyloid, the tau, inflammation, and blood perfusion. So you could think of Viagra as a way to solve one piece of that puzzle. It might help the perfusion of the brain, but at the same time, we can't ignore the other mechanisms.”
PDE5 inhibitors and Alzheimer’s
Viagra is in a class of drugs called phosphodiesterase 5 (PDE5) inhibitors. These are drugs that get in the way of, or change, certain types of chemical reactions in your blood. PDE5 inhibitors relax blood vessels and reduce inflammation.
In animal studies, researchers found that PDE5 inhibitors may help prevent cognitive impairment because of the increased flow to the brain. The results weren’t conclusive, and researchers haven’t repeated the studies on humans.
Can Viagra Help Reduce Alzheimer’s Risk?
Because of evidence that tau levels may be reduced in people who take Viagra and the benefits it has on brain blood vessel health in general, it’s possible the drug may become an Alzheimer’s risk reducer. But doctors aren’t recommending it for that use just yet.
What the science says
In the Journal of Alzheimer’s large, real-world analysis of patient data from two databases, Alzheimer’s cases were 30%-54% fewer among people who took Viagra than those who didn’t. But even though the study shows an association between lower Alzheimer’s risk and Viagra use, they don’t prove cause and effect.
The studies did adjust for some factors that could have an effect on outcomes, but the results aren’t enough to draw sure conclusions, says Younes.
“You don't know if people were on Viagra because they were healthy anyway, compared to the other group of patients they included, like the people who were on medications for pulmonary hypertension and kidney failure, which are more severe diseases,” Younes says.
The analysis also relies completely on a review of records instead of clinical trials, which isn’t “primary evidence.” Conclusive data would need to come from controlled, prospective trials instead of retrospective studies.
“I would present this study as interesting evidence,” says Younes. “I think the hypothesis, which has been there for a while, is really interesting. Viagra basically dilates the blood vessels. And that dilation of blood vessels is hypothesized to improve brain perfusion or blood to the brain, which can have positive effects.”
Does Viagra affect brain health?
Chronic damage to small blood vessels in your brain is the most common cause of dementia. In summer 2024, UK-based research published in Circulation Research showed that Viagra can get into the blood vessels of your brain, improving blood flow to the area and improving blood vessel function in those at a higher risk of vascular dementia.
Researchers saw this increased blood flow with MRI scans and ultrasounds. Experts note that larger clinical studies are needed before they recommend it as a preventative treatment for dementia.
Are There Any Dangers Related to Alzheimer’s and Viagra?
You should talk to your doctor before taking any medication. They don’t currently recommend Viagra as a prevention or treatment for Alzheimer’s.
Viagra can cause side effects, including:
- Headache
- Heartburn
- Diarrhea
- Nausea
- Flushing (feeling of warmth)
- Nosebleeds
- Numbness, burning, or tingling in the arms, hands, feet, or legs
- Pain in muscles, back, arms, or legs
- Changes in color vision (seeing a blue tinge on objects or having difficulty telling the difference between blue and green)
- Sensitivity to light
- Nasal congestion
Other drugs you take may interact with Viagra, causing serious side effects.
Understanding Drug Repurposing
When researchers discover a new use for a drug that’s already been FDA approved for a different condition, it’s called drug repurposing. Repurposing a drug can drastically cut the time it takes for a drug to become available to the public.
“If we had to create a new medication for every single disease starting from zero, it would take 10 years to go from inception all the way to clinical trials,” says Younes.
Once the FDA gives approval for a specific use for a drug, it has passed certain safety benchmarks and researchers have noted its side effects. Instead of starting from zero, researchers can start further along in the process. This can also cut the cost for the medication in the end, too.
Viagra is FDA approved for erectile dysfunction. In order to see if it’s an effective and safe treatment for Alzheimer’s disease, researchers have to do clinical trials to figure out questions such as:
- Is this medication safe for an older population?
- What is the right dose for treating Alzheimer’s?
- What side effects might an older population have on this dose?
Takeaways
Recent studies suggest sildenafil (Viagra) may lower Alzheimer's risk. People who have taken the drug have improved blood flow in the brain and reduced toxic protein buildup that’s common in the disease. But more studies and clinical trials are needed before the medical community can recommend Viagra as a preventative or treatment for Alzheimer’s.
