How Metformin Works: Scientists Discover the Diabetes Drug’s Main Brain Mechanism
- Metformin, the second most commonly prescribed medication in the United States in 2023, has been widely used to treat type 2 diabetes since the mid-20th century, yet scientists...
- First synthesized by scientists in 1922, metformin became a foundational treatment for type 2 diabetes due to its strong glucose-lowering effects.
- To test whether metformin's activity extends to the central nervous system, Fukuda's research team utilized a mouse model.
Metformin, the second most commonly prescribed medication in the United States in 2023, has been widely used to treat type 2 diabetes since the mid-20th century, yet scientists have just mapped its mechanism to the brain rather than solely the liver or gut. According to a study published in 2025 in Science Advances, the decades-old drug relies on a neural pathway to lower blood glucose levels, fundamentally shifting how researchers view its therapeutic reach.
Decades of Prescribing a Widely Used Diabetes Drug
First synthesized by scientists in 1922, metformin became a foundational treatment for type 2 diabetes due to its strong glucose-lowering effects. For generations, medical understanding held that the medication worked primarily by reducing glucose output in the liver or by acting through the gut. According to neurobiologist Makoto Fukuda from Baylor College of Medicine, it has been widely accepted that metformin lowers blood glucose primarily through hepatic mechanisms, though other studies have pointed to gastrointestinal pathways.
Uncovering the Brain’s Role in Glucose Metabolism
To test whether metformin’s activity extends to the central nervous system, Fukuda’s research team utilized a mouse model. Investigators bred mice genetically modified to lack the protein Rap1 in a specific region of the hypothalamus known as the ventromedial nucleus of the hypothalamus, or VMH. In previous work from the Baylor laboratory, researchers established that Rap1 in the VMH helps regulate whole-body glucose metabolism and energy balance. When the Rap1 gene was deleted in mice fed a high-fat diet to mimic type 2 diabetes, metformin failed to lower their blood glucose levels. While these Rap1-deficient mice still responded to other anti-diabetic treatments like insulin and GLP-1 agonists, they showed no response to metformin. This outcome indicates that the drug relies on the VMH Rap1 pathway to achieve its therapeutic effect, according to the research team.
Direct Brain Injections Reveal High Sensitivity
To confirm the brain’s direct involvement, the researchers administered small doses of metformin directly into the brains of obese mice. The experiment demonstrated that injecting as little as 1 microgram of the drug significantly reduced blood glucose levels. This dose is several thousand times lower than the amounts required for oral or peripheral administration in rodent studies, suggesting that the brain is highly sensitive to metformin. Further analysis revealed that metformin operates within the brain by activating SF1 neurons, which govern vital metabolic processes including blood sugar levels, appetite, and energy balance. This discovery expands medical understanding beyond the initial perspective of AMP-activated protein kinase-dependent hepatic glycemic improvement, pointing instead to multiple modes of action across peripheral organs and the central nervous system.