Hundreds of millions of people with Type 2 diabetes have been prescribed metformin by physicians for more than 60 years. Because of its effectiveness, affordability, and reasonably forgiving safety profile when compared to other options, it became the standard first-line medication. It decreased the liver’s production of glucose. It enhanced the body’s use of insulin. That was the recognized mechanism, the accepted science, and the solution taught to medical students. However, it turns out that a crucial component was missing from the complete solution.
| Key Information | Details |
|---|---|
| Drug Name | Metformin — the most commonly prescribed first-line treatment for Type 2 diabetes |
| Years in Use | More than 60 years |
| Research Institution | Baylor College of Medicine, Houston, Texas (lead researcher: Dr. Makoto Fukuda, Associate Professor of Pediatrics and Nutrition) |
| Collaborating Institutions | Louisiana State University; Nagoya University (Japan); Meiji University (Japan) |
| Published In | Science Advances (2025) |
| Key Discovery | Metformin works through a previously unknown brain pathway via a protein called Rap1 in the ventromedial hypothalamus (VMH) — in addition to its known liver and gut mechanisms |
| Key Brain Cells | SF1 neurons in the VMH become electrically active when metformin is introduced to the brain |
| Brain Dose Finding | Brain tissue responds to doses thousands of times lower than standard oral doses |
| Additional Potential Benefits | Slowing brain aging, protecting cognitive function, reducing dementia risk, 30% lower mortality risk before age 90 in postmenopausal women (vs. sulfonylurea) |
| Common Side Effects | Gastrointestinal issues (nausea, diarrhea, abdominal discomfort) in up to 75% of users |
| Funding | National Institutes of Health, American Heart Association, American Diabetes Association |
| Reference Links | European Medical Journal — Metformin: Brain Pathway to Lower Blood Sugar Revealed / Science Alert — After 60 Years, Diabetes Drug Revealed to Unexpectedly Affect The Brain |
Together with researchers from Louisiana State University, Nagoya University, and Meiji University in Japan, researchers at Baylor College of Medicine have discovered a brain-based mechanism by which metformin regulates blood sugar. The research, which was published in Science Advances, focuses on a tiny protein called Rap1 that is found in the ventromedial hypothalamus, or VMH, a part of the brain. That protein had no bearing on anyone’s comprehension of this medication for sixty years. It seems to be at the center of it now.
Some of the same researchers had previously discovered that Rap1 in the VMH has an impact on glucose metabolism, which led to the discovery. Then, under the direction of Dr. Makoto Fukuda, the Baylor team started looking into whether metformin was having any unnoticed effects on the brain. They bred Rap1-deficient mice in the VMH and fed them high-fat diets to mimic Type 2 diabetes in order to test this. The mice’s blood sugar did not improve when given small doses of metformin. The same animals continued to respond normally to other diabetes treatments, such as insulin and GLP-1 agonists. The issue was unique to the brain pathway of metformin. “It’s been widely accepted that metformin lowers blood glucose primarily by reducing glucose output in the liver,” Fukuda stated. “We found that while the liver and intestines need high concentrations of the drug to respond, the brain reacts to much lower levels.”
One of the more startling discoveries is that final detail. Blood sugar levels significantly decreased even when the team injected minuscule amounts of metformin directly into the brains of diabetic mice—doses thousands of times lower than a typical oral dose. It turns out that the brain is reacting to more than just the medication. It’s acting in an unusually sensitive manner. Only in the presence of Rap1 did the SF1 neurons in the VMH become electrically active when metformin reached them. Metformin did not result in any electrical activity or improvement of blood sugar in mice that were specifically engineered to lack Rap1 in those neurons. The route was verified. The researchers came to the conclusion that it is a crucial mediator of the drug’s effects.
Reading this research gives me the impression that it modifies the metformin question rather than merely adding a detail. For many years, it was assumed that this medication mainly affected the liver with some involvement of the gut. It has long been known that the brain plays a major role in controlling the body’s overall glucose metabolism. However, it is truly surprising that a medication taken orally for its effects on the liver was also acting at doses much lower than those affecting other organs on particular neurons in a particular area of the brain. It’s the kind of discovery that prompts researchers to examine decades’ worth of clinical data and wonder what else might have been going on that no one had measured.
There are two possible outcomes. Drug development is the more pressing one. The majority of diabetes drugs have no effect on the brain. More effective or targeted therapies may result if the VMH Rap1 pathway can be directly targeted, either by improving metformin or by creating new compounds that interact with the same pathway. Regarding this, Fukuda was straightforward: “These findings open the door to developing new diabetes treatments that directly target this pathway in the brain.”
Though perhaps more intriguing, the second approach is more expansive and speculative. The effects of metformin that go beyond blood sugar regulation have drawn increasing attention. It has been investigated as a possible medication to slow down aging; some studies have referred to it as a gerotherapeutic, which can prevent DNA damage and increase gene activity linked to longevity. According to a 2025 study with over 400 postmenopausal women, metformin users had a roughly 30% lower chance of passing away before the age of 90 than those using another diabetes medication. Additionally, there is evidence that it may prevent some of the cognitive decline linked to Type 2 diabetes and lower the risk of dementia. The liver-and-gut model did not adequately account for any of those effects. The Baylor researchers say they intend to look into the possibility that some or all of them are related to the brain pathway identified by Fukuda’s team.
It’s difficult to ignore the fact that one of the oldest, most widely used, and researched medications in the world of medicine recently uncovered a mechanism that had been concealed all along. That is both humble and, subtly, uplifting. The story of metformin is not yet complete. It seems to be only becoming more intricate.
