You might have heard that Viagra, the little blue pill that resurrects sagging erections, is being touted as a potential prophylactic against Alzheimer’s disease.

It’s not a new idea. Research going back at least 20 years has suggested Viagra could be an effective treatment for Alzheimer’s, vascular dementia and stroke.

In the latest study, researchers from the Cleveland Clinic analysed more than seven million insurance claims for prescriptions of a variety of drugs and looked at the rate of subsequent development of Alzheimer’s disease.

Prevention is the holy grail

They found that prescriptions for sildenafil (the active ingredient in Viagra) were associated with a 69 per cent reduced risk of Alzheimer’s in claimants.

The thinking is that because a significant number of people who used sildenafil didn’t develop the brain-wasting disease, then maybe sildenafil had prevented Alzheimer’s.

It’s an exciting idea because Alzheimer’s prevention is the holy grail, more so than finding an effective treatment – because damage to the brain from the disease can’t be reversed.

It was also found to be more effective than other drugs that treat cardiovascular disease.

The study included data showing that sildenafil “lowered the amount of an Alzheimer’s-related protein tau in brain cells programmed from stem cells from one person who had Alzheimer’s”.

Reaction from brain scientists has been largely encouraging, and in some cases were enthusiastic, although a few said they weren’t too impressed. For a range of reactions see here.

Only large-scale clinical trials will settle the argument.

Previous research

In a 2002 study in rats, Viagra appeared to reduce the effects of stroke by helping the brain heal itself.

The researchers gave rats Viagra for six days after inducing an ischemic stroke, a blockage of an artery that supplies blood to the brain.

After 28 days, they found the rats that received the drug grew significantly more new brain cells, performed better on agility, sensory, and muscle function tests.

 In 2014, scientists from St George’s, University of London began a clinical trial in which UK pensioners were given tadalafil, a Viagra-like drug, to see if it might prevent vascular dementia – which is often caused by damage to the small blood vessels, resulting in reduced blood flow to brain tissue.

This blood vessel damage – known as ‘small vessel disease’ – is seen in the brains of 50 to 70 per cent of elderly people.

The hope was that tadalafil would increase blood to the brain, just as it does to the penis. Results pending.

A 2017 study of 12 Alzheimer’s patients found that a single dose of sildenafil improved cerebral blood blow and increased cerebral oxygen metabolism.

A 2020 study from Harvard and Cambridge found that the phosphodiesterase 5 (PDE5) inhibitors in sildenafil seemed to improve the brain’s ability to clear misfolded proteins found in Alzheimer’s and Parkinson’s patients.

PDE5 is a type of drug that can affect blood flow and how cells communicate in the body.

The PDE5 that is used to treat erectile dysfunction is also used to treat pulmonary arterial hypertension.