metformin
Metformin (Glucophage) is an oral biguanide for type 2 diabetes. It lowers blood glucose mainly by reducing glucose output from the liver and by helping the body respond better to its own insulin. It is used with diet and exercise in adults and children aged 10 years and older.
This page is based on FDA prescribing information for metformin hydrochloride tablets, cross-checked with MedlinePlus and the National Cancer Institute dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
The liver is a glucose warehouse. Between meals it releases sugar into the blood to keep levels steady, but in type 2 diabetes the warehouse doors stick open and too much glucose leaks out. Metformin closes those doors: it tells the liver to release less stored sugar and helps the body's own insulin work better, so blood glucose settles back into range without adding extra insulin.
In simple terms
Metformin lowers blood glucose in three main ways. First, it reduces the amount of glucose the liver makes and releases between meals. Second, it decreases how much glucose is absorbed from food in the gut. Third, it makes the body's tissues respond better to insulin, so cells take up glucose more effectively. Because metformin does not stimulate insulin production, it rarely causes low blood sugar when used on its own. It is taken by mouth and works alongside diet and exercise in people with type 2 diabetes; it is not used for type 1 diabetes.
In depth
Metformin inhibits complex I of the mitochondrial respiratory chain, raising the cellular AMP-to-ATP ratio and activating AMP-activated protein kinase (AMPK). AMPK activation suppresses hepatic gluconeogenesis and enhances insulin sensitivity and fatty acid oxidation, ultimately lowering circulating glucose. Metformin also reduces intestinal absorption of glucose. Because its action does not depend on insulin secretion, metformin monotherapy rarely causes hypoglycemia. Preclinical studies suggest antineoplastic effects through AMPK-mediated or AMPK-independent inhibition of mTOR signaling, although this is not an approved use.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
Metformin lowers blood glucose in three main ways.
- The liver keeps releasing glucose it makes from other molecules (gluconeogenesis).
- Metformin mainly slows the liver's glucose output (gluconeogenesis).
- Body tissues respond better to their own insulin, so more glucose leaves the blood.
- Blood glucose settles into range without pushing the pancreas to release extra insulin.
Target: Mitochondrial respiratory chain complex I
The first enzyme of the mitochondrial energy chain; partial inhibition in liver cells shifts the cell's energy balance toward AMP, activates AMPK, and turns down glucose production.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in United States
FDA- As an adjunct to diet and exercise to improve glycemic control in adults and pediatric patients 10 years of age and older with type 2 diabetes mellitus
Official sources
The statements on this page trace back to these records.
- U.S. Food and Drug Administration: metformin prescribing information
U.S. Food and Drug Administration
- MedlinePlus: metformin
MedlinePlus, U.S. National Library of Medicine
- National Cancer Institute: metformin hydrochloride
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.