Scientists Discover Metformin Works Through Your Brain—After 60 Years of Use

After six decades of prescribing metformin to millions of people with type 2 diabetes, scientists have discovered the drug works directly in the brain—a finding that could revolutionize how we treat diabetes and potentially other age-related conditions.

Researchers from Baylor College of Medicine identified a specific brain pathway that metformin targets, in addition to its well-known effects on the liver and gut. This discovery explains why the drug has been so effective at managing blood sugar levels and hints at why it may also slow brain aging.

How Does Metformin Actually Work in the Brain?

The research team focused on a brain region called the ventromedial hypothalamus (VMH), which acts as a control center for glucose metabolism throughout the body. They found that metformin travels directly to this brain area and works by turning off a protein called Rap1.

"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," said Makoto Fukuda, a pathophysiologist at Baylor College of Medicine. "We looked into the brain as it is widely recognized as a key regulator of whole-body glucose metabolism."

When researchers tested mice that were bred without the Rap1 protein, metformin had no effect on their diabetes-like condition—even though other diabetes drugs still worked. This provided strong evidence that metformin's brain pathway is unique and essential for its effectiveness.

What Makes This Brain Discovery So Important?

The findings could lead to more targeted diabetes treatments that work specifically through brain pathways. The research team identified that metformin activates specific neurons called SF1 neurons in the VMH, suggesting future treatments could target these cells directly.

Understanding metformin's brain effects also helps explain the drug's broader health benefits beyond diabetes management:

• Longevity Effects: A 2025 study of over 400 postmenopausal women found those taking metformin had a 30% lower risk of dying before age 90 compared to those taking a different diabetes drug called sulfonylurea
• Brain Aging: Previous research has shown metformin can reduce wear and tear in the brain and limit deoxyribonucleic acid (DNA) damage associated with aging
• COVID Protection: Studies have found the drug may reduce the risk of long COVID symptoms

"This discovery changes how we think about metformin," explained Fukuda. "It's not just working in the liver or the gut, it's also acting in the brain. We found that while the liver and intestines need high concentrations of the drug to respond, the brain reacts to much lower levels."

What Does This Mean for Diabetes Treatment?

Metformin remains one of the most prescribed diabetes medications worldwide because it's effective, long-lasting, and relatively affordable. It works by reducing glucose production in the liver and increasing how efficiently the body uses insulin to manage type 2 diabetes symptoms.

However, side effects aren't uncommon—gastrointestinal problems like nausea, diarrhea, and abdominal discomfort affect up to 75% of people taking the medication. Understanding how metformin works in the brain could help researchers develop more targeted treatments with fewer side effects.

"These findings open the door to developing new diabetes treatments that directly target this pathway in the brain," said Fukuda. The research team plans to investigate whether the same brain signaling pathway is responsible for metformin's other documented effects on brain health and aging.

While these findings need to be confirmed in human studies, they represent a significant step forward in understanding one of medicine's most widely used drugs. For the millions of people managing type 2 diabetes, this research offers hope for more effective treatments that could work through entirely new mechanisms in the brain.