Metformin drug prescribed to 120 million worldwide found to have surprise impact on brain

Joe Harker
2026-03-26T14:20:38.135Z
News

It has been prescribed for decades but scientists haven't been sure about its other effects

Scientists have found evidence to indicate the drug metformin has an important impact on the brain, which could mean it would be viable for other treatments.

It's typically issued to patients to treat type 2 diabetes and gestational diabetes, though it's given to those at high risk of type 2 diabetes to try and prevent them from developing it. It's also taken to improve fertility for those with polycystic ovary syndrome (PCOS) by encouraging monthly menstruation and lowering the risk of miscarriages.

Metformin is estimated to be prescribed to around 120 million people and improves the way the body handles insulin to lower blood sugar levels, but researchers have found another effect it has.

Last year, a team of researchers from Baylor College of Medicine found that metformin also affected the brain in a specific way.

Millions of people around the world are prescribed metformin (Scott Olson/Getty Images)

They explained that despite people taking metformin for over 60 years, the full extent of what it does to the human body is not known to scientists, though the new research shed light on the impact it has on the brain.

How metformin affects the brain

"It’s been widely accepted that metformin lowers blood glucose primarily by reducing glucose output in the liver. Other studies have found that it acts through the gut," Dr Makoto Fukuda, Associate Professor of Paediatrics-Nutrition at Baylor said.

"We looked into the brain as it is widely recognised as a key regulator of whole-body glucose metabolism. We investigated whether and how the brain contributes to the anti-diabetic effects of metformin."

There's a part of your brain known as the ventromedial hypothalamus, where a protein called Rap1, which has an impact on your body's metabolism of glucose, can be found.

The scientists discovered that when metformin works, it turns off the Rap1 protein in this part of the brain, and when testing on genetically modified mice without this protein in that part of their brain, they found it didn't work.

Feeding the animals a high-fat diet to mimic the effects of type 2 diabetes, they found that metformin didn't lower blood sugar in mice without Rap1.

Tests on mice found metformin had a significant impact on their brains (Getty Stock Images)

Other diabetes treatments like insulin and GLP-1 agonists (the same family of drugs as Ozempic) still worked.

They then injected metformin into the mice's brains and found a significant drop in blood sugar, even at a dose much lower than when taken orally.

This discovery shows the drug, when taken normally, needs to affect a change in the brain to properly work, and Professor Fukuda said more research was needed that could lead to new treatments for diabetes or even slowing down the ageing of the brain.

He said: "These findings open the door to developing new diabetes treatments that directly target this pathway in the brain.

"In addition, metformin is known for other health benefits, such as slowing brain aging. We plan to investigate whether this same brain Rap1 signalling is responsible for other well-documented effects of the drug on the brain."

What are the side effects of metformin?

Some people may experience side effects (Getty Stock Images)

According to the NHS, the common side effects of metformin can occur in one in 100 people, which include:

Nausea

Vomiting

Diarrhoea

Stomach ache

Loss of appetite

A metallic taste in your mouth

Metformin can also cause a vitamin B12 deficiency. If you experience symptoms such as tiredness, muscle weakness, or mouth ulcers and have pale or yellow skin, consult your doctor, who may prescribe B12 supplements.