This article was originally written and posted on March 26, 2026, and was updated on April 18, 2026
Practitioner’s Preface
Metformin is the most common type 2 diabetes medication prescribed; however, until very recently its mechanism of action has been largely unknown. It has been widely accepted that this diabetes medication acts mainly by reducing glucose produced by the liver and by altering gut function [3]. A recent study suggests that Metformin works directly in the brain.
Why Is Metformin Prescribed for PCOS?
Metformin is often prescribed for conditions driven by insulin resistance, including type 2 diabetes and Polycystic Ovarian Syndrome (PCOS), and new studies show its blood sugar benefits are tied to brain pathways.
In my almost 18 years of private clinical practice and my licensure in British Columbia, Alberta, and Ontario, I have encountered many people taking Metformin. Originally, it was always prescribed for managing the high blood sugar associated with type 2 diabetes. In the last 10 years, I have seen it prescribed to young women with Polycystic Ovarian Syndrome (PCOS), which makes sense because the underlying driver of PCOS is insulin resistance. In the case of PCOS, the insulin resistance is in the ovaries, rather than in the muscle and liver, like in type 2 diabetes. I have also seen people take Metformin to reduce their risk factors for Alzheimer’s disease, which has been referred to as “type 3 diabetes”. Until very recently, we knew Metformin worked, but not how. This recent study provides that explanation.
How Does Metformin Affect the Body?
Traditional medical science has long established that Metformin works by lowering liver glucose production and changing gut activity. New evidence demonstrates that the brain is also a major driver in how this medication lowers daily blood sugar levels across different populations.
It has been known since 1967 that Metformin acts by reducing glucose produced in the liver [2], and since 1994 that this diabetes medication alters gut function [3], but a study published at the end of June 2025 shows that Metformin works directly in the brain.
Scientists have known since 2013 that the brain was a key regulator of blood sugar (glucose) [4],[5], but how the brain contributed to the blood glucose-lowering effect of Metformin was unknown.
How Does Metformin Affect Hunger?
Metformin travels to a specific area of the brain called the ventromedial hypothalamus to switch off a protein called Rap1. This vital interaction helps reset the brain pathway that controls appetite and signals that the body is no longer hungry.
A preliminary animal study in 2021 identified a brain protein called Repressor/Activator Protein 1 (Rap1) that impacts blood sugar metabolism in the ventromedial hypothalamus (VMH) [6], a part of the brain that has long been thought of as the “satiety center“[7] that signals that a person is no longer hungry.
A new animal study, published on July 30, 2025, reported that Metformin reaches the ventromedial hypothalamus, where it turns off Rap1. At clinically relevant doses, Metformin’s ability to lower blood sugar depends entirely on this brain pathway, and without this interaction in the hypothalamus, the medication’s glucose-lowering effects are significantly less.
How Does Rap1 Cause Leptin Resistance?
Rap1 is a specific brain protein that controls how the body senses leptin, the fullness hormone. In people with obesity, this protein becomes overactive and causes leptin resistance, but Metformin blocks this overactivity to restore natural fullness signals and stop overeating.
Rap1 (Repressor/Activator Protein 1) serves as a satiety switch in the brain, regulating energy balance and metabolism. The hypothalamus serves as the brain’s “command center” for hunger, and Rap1 is a key player in how the brain senses leptin, the hormone that signals the body that the person is full (called “satiety“).
When Rap1 is functioning normally, it helps transmit the signal to stop eating; however, in people with obesity, Rap1 can become overactive in the hypothalamus, contributing to leptin resistance. This means that the brain stops responding to leptin’s signal to stop eating.
Metformin appears to suppress overactive Rap1 signaling in the hypothalamus, and by turning down the expression of this protein, Metformin helps restore the brain’s sensitivity to leptin, which helps improve blood sugar levels and lower body weight [1]. By silencing overactive Rap1, Metformin clears the interference caused by leptin resistance, allowing the brain to respond once again to the signals that tell the body that it is full.
Can Metformin Help With Alzheimer’s?
Metformin passes through the blood-brain barrier into brain tissue in safe, effective amounts, and once inside, can help improve memory, attention, and general brain functioning in people struggling with Alzheimer’s disease or chronic cognitive decline.
The scientific literature has demonstrated that Metformin crosses the blood-brain barrier in clinically relevant amounts in both animals [8] and humans [9]. This has important implications for Alzheimer’s disease, where Metformin has already been reported to improve executive functioning and is suggested to improve learning, memory, and attention [9].
Findings in this new study suggest that the brain is exposed to approximately 1/10 the concentration of Metformin present in the bloodstream, and that as little as 1 μg of Metformin in the brain is sufficient to correct high blood sugar (hyperglycemia). This 1:10 ratio establishes an important safety threshold, demonstrating that Metformin can affect hypothalamic signaling and restore satiety (i.e., feeling full) without requiring high dosages that could lead to neurological side effects.
What Is the Future of Metformin Beyond Treating Diabetes?
Understanding that this common diabetes medication directly alters brain signaling opens new pathways for medical treatments. These discoveries show that its protective health properties extend far beyond standard blood sugar control in the liver and gut systems.
Scientists have long known of Metformin’s effect on the liver and the gut, and knowing that this diabetes medication crosses the blood-brain barrier and has a positive effect on whole-body blood sugar and functioning in people with Alzheimer’s disease may inform how this medication may be prescribed in the future, beyond its role in type 2 diabetes.
Linking metabolic health medications directly to brain pathways provides a clearer picture for people managing chronic conditions. This deeper scientific insight helps motivate individuals to combine prescription therapies with targeted diet and lifestyle changes to reach optimal health.
It is helpful to finally be able to provide a partial explanation to my clients who are taking Metformin on how it works. The blood-brain barrier interaction makes sense in how Metformin works for those with type 2 diabetes and Alzheimer’s. I think more needs to be known about Metformin’s mechanism of action to be able to explain its benefit in lowering insulin resistance in PCOS, where blood sugar is often normal.
More Info
Personalized nutrition coaching offers structured meal support to help reverse insulin resistance and manage blood sugar levels safely, and connects lab test results with easy lifestyle habits to restore metabolic health and natural fullness without constant hunger.
If you would like more information, learn about me and why I do what I do. For those wanting to lower the high blood sugar of type 2 diabetes or pre-diabetes, have a look at the Comprehensive Dietary Package that I offer. For women with PCOS, learn more about the Polycystic Ovarian Syndrome Package to lower the insulin resistance that drives the disorder.
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Clinical Summary
Metformin treats high blood sugar by decreasing liver glucose production, altering gut pathways, and turning off overactive proteins in the brain’s hunger center. This combined action reverses leptin resistance and helps restore normal fullness signaling throughout the entire body.
Q: How does Metformin affect the brain’s satiety center?
A: Metformin crosses the blood-brain barrier and enters the ventromedial hypothalamus, where it turns off Rap1 (Repressor/Activator Protein 1). By suppressing Rap1 signaling, Metformin restores the brain’s sensitivity to leptin, the hormone that signals fullness.
Q: What is the role of Rap1 in obesity and leptin resistance?
A: In individuals with obesity, the brain protein Rap1 can become overactive in the hypothalamus. This overactivity contributes to leptin resistance, where the brain stops responding to signals to stop eating. Metformin corrects this by turning down overactive Rap1 expression.
Q: Can Metformin help with Alzheimer’s disease functioning?
A: Scientific literature suggests Metformin crosses the blood-brain barrier in clinically relevant amounts and can improve executive functioning, learning, memory, and attention in individuals with Alzheimer’s disease, often referred to as ‘Type 3 Diabetes.’
References
- Hsiao-Yun Lin et al. Low-dose metformin requires brain Rap1 for its antidiabetic action.Sci. Adv.11,eadu3700(2025).DOI:10.1126/sciadv.adu3700
- F. Meyer, M. Ipaktchi, H. Clauser, Specific inhibition of gluconeogenesis by biguanides. Nature 213, 203–204 (1967).
- C. J. Bailey, K. J. Mynett, T. Page, Importance of the intestine as a site of metformin-stimulated glucose utilization. Br. J. Pharmacol. 112, 671–675 (1994).
- B. E. Grayson, R. J. Seeley, D. A. Sandoval, Wired on sugar: The role of the CNS in the regulation of glucose homeostasis. Nat. Rev. Neurosci. 14, 24–37 (2013).
- M. W. Schwartz, R. J. Seeley, M. H. Tschop, S. C. Woods, G. J. Morton, M. G. Myers, D. D’Alessio, Cooperation between brain and islet in glucose homeostasis and diabetes. Nature 503, 59–66 (2013).
- K. Kaneko, H. Y. Lin, Y. Fu, P. K. Saha, A. B. De la Puente-Gomez, Y. Xu, K. Ohinata, P. Chen, A. Morozov, M. Fukuda, Rap1 in the VMH regulates glucose homeostasis. JCI Insight 6, e142545 (2021).
- King BM. The rise, fall, and resurrection of the ventromedial hypothalamus in the regulation of feeding behavior and body weight. Physiol Behav. 2006 Feb 28;87(2):221-44. doi: 10.1016/j.physbeh.2005.10.007. Epub 2006 Jan 18. PMID: 16412483.
- A. Thinnes, M. Westenberger, C. Piechotta, A. Lehto, F. Wirth, H. Lau, J. Klein, Cholinergic and metabolic effects of metformin in mouse brain. Brain Res. Bull. 170, 211–217 (2021).
- A. M. Koenig, D. Mechanic-Hamilton, S. X. Xie, M. F. Combs, A. R. Cappola, L. Xie, J. A. Detre, D. A. Wolk, S. E. Arnold, Effects of the insulin sensitizer metformin in alzheimer disease: Pilot data from a randomized placebo-controlled crossover study. Alzheimer Dis. Assoc. Disord. 31, 107–113 (2017).
I am a Registered Dietitian Nutritionist and the owner of BetterByDesign Nutrition Ltd. With a postgraduate degree in Human Nutrition and a background as a published mental health nutrition researcher, I have been dedicated to supporting my clients’ clinical needs since 2008.
I hold active professional licenses in BC (CHPBC), Alberta (CDA), and Ontario (CDO), allowing me to provide regulated Medical Nutrition Therapy across these provinces. My expertise spans chronic disease management, complex digestive health, and therapeutic diets. I am deeply passionate about helping people reclaim their health, rooted in my firm belief that Nutrition is BetterByDesign©.