Antibiotics, antivirals, vaccinations and anti-inflammatory medication are associated with reduced risk of dementia, according to new research that looked at health data from over 130 million individuals.

The study identified several drugs already licensed and in use that have the potential to be repurposed to treat dementia.

Despite intensive efforts, progress in identifying drugs that can slow or even prevent dementia has been disappointing.

Until recently, dementia drugs were effective only for symptoms and have a modest effect. Recently, lecanemab and donanemab have been shown to reduce the build-up in the brain of amyloid plaques – a key characteristic of Alzheimer’s disease – and to slow down progression of the disease, but the National Institute for Health and Care Excellence (NICE) concluded that the benefits were insufficient to justify approval for use within the NHS.

Scientists are increasingly turning to existing drugs to see if they may be repurposed to treat dementia. As the safety profile of these drugs is already known, the move to clinical trials can be accelerated significantly.

Dr Ben Underwood, from the Department of Psychiatry at the University of Cambridge and Cambridgeshire and Peterborough NHS Foundation Trust, said: “We urgently need new treatments to slow the progress of dementia, if not to prevent it.

“If we can find drugs that are already licensed for other conditions, then we can get them into trials and – crucially – may be able to make them available to patients much, much faster than we could do for an entirely new drug.

“The fact they are already available is likely to reduce cost and therefore make them more likely to be approved for use in the NHS.”

Dr Underwood, together with Dr Ilianna Lourida from the University of Exeter, led a systematic review of existing scientific literature to look for evidence of prescription drugs that altered the risk of dementia. Systematic reviews allow researchers to pool several studies where evidence may be weak, or even contradictory, to arrive at more robust conclusions.

In total, the team examined 14 studies that used large clinical datasets and medical records, capturing data from more than 130 million individuals and one million dementia cases.

Although they found a lack of consistency between studies in identifying individual drugs that affect the risk of dementia, they identified several drug classes associated with altered risk.

One unexpected finding was an association between antibiotics, antivirals and vaccines, and a reduced risk of dementia. This finding supports the hypothesis that common dementias may be triggered by viral or bacterial infections, and supports recent interest in vaccines, such as the BCG vaccine for tuberculosis, and decreased risk of dementia.

Anti-inflammatory drugs such as ibuprofen were also found to be associated with reduced risk. Inflammation is increasingly being seen to be a significant contributor to a wide range of diseases, and its role in dementia is supported by the fact that some genes that increase the risk of dementia are part of inflammatory pathways.

The team found conflicting evidence for several classes of drugs, with some blood pressure medications and anti-depressants and, to a lesser extent, diabetes medication associated with a decreased risk of dementia and others associated with increased risk.

Dr Ilianna Lourida from the National Institute for Health and Care Research Applied Research Collaboration South West Peninsula (PenARC), University of Exeter, said: “Because a particular drug is associated with an altered risk of dementia, it doesn’t necessarily mean that it causes or indeed helps in dementia.

“We know that diabetes increases your risk of dementia, for example, so anyone on medication to manage their glucose levels would naturally also be at a higher risk of dementia – but that doesn’t mean the drug increases your risk.

“It’s important to remember that all drugs have benefits and risks. You should never change your medicine without discussing this first with your doctor, and you should speak to them if you have any concerns.”

The conflicting evidence may also reflect differences in how particular studies were conducted and how data was collected, as well as the fact that different medications even within the same class often target different biological mechanisms.

The UK government is supporting the development of an Alzheimer’s trial platform to evaluate drugs rapidly and efficiently, including repurposed drugs currently used for other conditions.

“Pooling these massive health data sets provides one source of evidence which we can use to help us focus on which drugs we should try first,” said Dr Underwood.

“We’re hopeful this will mean we can find some much-needed new treatments for dementia and speed up the process of getting them to patients.”