Most Common Type 2 Diabetes Medication Directly Affects the Brain

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Introduction

Metformin is the most common type 2 diabetes medication prescribed; however, its exact mechanism of action has been largely unknown until very recently. 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 Metfomin works directly in the brain.

Previously Known Metformin Mechanisms of Action

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 in 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.

Effects of Metformin on the Brain

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 Metfomin 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.

Rap 1 Works as the Satiety Switch

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.

Metformin Crosses the Blood-Brain Barrier

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 Metfomin 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.

Final Thoughts

Scientists have long known of Metfomin’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.

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References

  1. 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
  2. F. Meyer, M. Ipaktchi, H. Clauser, Specific inhibition of gluconeogenesis by biguanides. Nature 213, 203–204 (1967).
  3. 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).
  4. 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).
  5. 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).
  6. 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).
  7. 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.
  8. 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).
  9. 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).
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