Moleculium

CID 4091

C4H11N5

Metformin

  • C 4
  • H 11
  • N 5
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20 atoms, 19 bonds.
Ball-and-stick model of metformin: 4 carbon atoms, 11 hydrogen atoms and 5 nitrogen atoms, 19 bonds (17 single, 2 double). Carbon is grey, hydrogen white, nitrogen blue.
IUPAC name
3-(diaminomethylidene)-1,1-dimethylguanidine
Molar mass
129.167(15) g/mol
Atoms
20
SMILES
CN(C)C(=N)N=C(N)N
InChIKey
XZWYZXLIPXDOLR-UHFFFAOYSA-N
PubChem CID
4091

Made of

C , Carbon, nonmetal H , Hydrogen, nonmetal N , Nitrogen, nonmetal
Structural formula of metformin. Each unlabelled corner is a carbon atom. It shows which atoms are joined to which, not the shape. The model above shows the shape. Structural formula of metformin, drawn flat from PubChem's 2D record: 4 carbon atoms, 11 hydrogen atoms and 5 nitrogen atoms, 19 bonds (17 single, 2 double). Each unlabelled corner is a carbon atom. Symbols carry their usual colours: nitrogen blue. A structural formula shows how the atoms are joined, not the shape of the molecule.

In 2014 US retail pharmacies filled prescriptions for metformin, alone or in combination products, for about 14.4 million people, on the count of the Food and Drug Administration (FDA). LiverTox, a liver-injury database of the National Library of Medicine and the US institute for diabetes, digestive and kidney diseases (NIDDK), calls metformin a first-line agent for type 2 diabetes.

Its molecule holds only carbon, hydrogen and nitrogen, with five nitrogen atoms to four carbons. FDA classes it as a biguanide, and ChEBI, a database of chemical entities of biological interest, describes it as biguanide with two methyl groups at position 1. The National Cancer Institute (NCI) drug dictionary lists the salt as 1,1-dimethylbiguanide hydrochloride. PubChem’s IUPAC name, 3-(diaminomethylidene)-1,1-dimethylguanidine, builds the molecule on one guanidine carrying both methyls instead, the rest of the chain becoming a diaminomethylidene group: a carbon holding two amino groups.

Structure and bonding

Metformin’s four carbons and five nitrogens form an open, branched chain with no ring, and eleven hydrogens complete the model’s 20 atoms and 19 bonds. Two carbons are methyl groups on an end nitrogen; the other two each hold three nitrogens and share the one between them. Ball-and-stick shows five blue nitrogens outnumbering the grey carbons. Each central carbon spreads its three bonds flat, the trigonal plane Chem1 describes for a carbon in a double bond. Labels show hydrogen on every nitrogen except the bridge and the methyl-bearing one.

Two C–N sticks are drawn doubled. From the =N–H end the bonds alternate, N=C–N=C, a pattern Chem1 calls a conjugated system, and the model fixes it in one placement. Space-filling merges the atoms into one compact shape, rounded where the two methyl groups crowd together. As drawn, metformin is the neutral base PubChem records, C4H11N5, while the medicine is metformin hydrochloride, a salt, in NCI’s drug dictionary. ChEBI names metformin(1+), one proton heavier, as its conjugate acid; Chem1 defines a conjugate pair as two species that differ by a single proton, gained or lost.

Where it turns up

FDA approved metformin in 1995, and it reaches patients only on prescription, as a single-ingredient product or combined with other diabetes drugs. NIDDK notes that it comes as pills and also as a liquid. Among its US brand names, NCI lists Glucophage, Glumetza and Fortamet. The World Health Organization includes it in its Model List of Essential Medicines as a blood-glucose-lowering drug for type 2 diabetes. HSDB, the Hazardous Substances Data Bank, records a veterinary use too.

The body does not break the molecule down. NCI’s thesaurus states that the kidneys excrete it unchanged, and HSDB adds that no metabolite of it has been identified in humans. ChEBI gives it the roles of xenobiotic, a substance foreign to the body, and environmental contaminant.

Why it matters

Left untreated, type 2 diabetes can bring heart disease, blindness and damage to the nerves and kidneys, according to FDA. Metformin lowers blood glucose in three ways the agency named: the liver makes less sugar, the intestines take up less, and the body responds better to its own insulin. HSDB credits most of the effect to the first of these and to stronger insulin action in muscle and fat. Metformin needs the body’s own insulin: HSDB states that insulin secretion must still be present for it to work properly.

Inside the cell the drug sets off a chain of events, according to NCI. Metformin blocks complex I, an enzyme of the respiratory chain in mitochondria. That raises the cell’s ratio of AMP (adenosine monophosphate) to ATP and activates another enzyme, AMP-activated protein kinase. In NCI’s account the cascade ends by preventing gluconeogenesis, the making of new glucose in the liver, while raising insulin sensitivity and the breakdown of fatty acids. HSDB states that the mechanisms by which the drug strengthens insulin’s effect are not fully understood.

Properties

Properties of metformin Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 4091.
Property Value Unit Source
Molecular formula (Hill order) C4H11N5
Molar mass 129.167(15)   g/mol g/mol IUPAC/CIAAW 2024
Carbon atoms 4
Hydrogen atoms 11
Nitrogen atoms 5
Bonds 19
Single bonds 17
Double bonds 2
PubChem molecular weight 129.16   g/mol g/mol PubChem

Safety

In April 2016 FDA required labelling changes that widened metformin’s use among some patients with reduced kidney function. FDA stated then that in some patients with poorly working kidneys, metformin could raise the risk of lactic acidosis, a serious and potentially deadly condition. Two of the four company reports to the European Chemicals Agency classify pure metformin as harmful if swallowed. Its full classification is in the PubChem Laboratory Chemical Safety Summary for metformin.

Questions

What does the 3D model of metformin show?

A branched chain with no ring, its eleven hydrogens unevenly spread. Six belong to the two methyl carbons, which hang from a single nitrogen at one end. The other five sit on nitrogen: two on each NH2 group of the far carbon and one on the =NH. No atom in the model carries a charge.

What is metformin hydrochloride?

It is the salt form of the drug. The National Cancer Institute's drug dictionary defines it as the biguanide metformin's hydrochloride salt, and HSDB lists metformin hydrochloride tablets. Metformin is made by reacting dimethylamine hydrochloride with dicyandiamide, HSDB records, and a 1965 US patent by J. J. Sterne (number 3174901) covers a preparation of it. The salt dissolves freely in water and slightly in alcohol, and hardly at all in ether or chloroform.

Can metformin cause low blood sugar?

HSDB describes metformin as antihyperglycaemic, acting against high blood sugar, rather than hypoglycaemic, driving blood sugar low, and adds that it does not make the pancreas release insulin. FDA stated in 2016 that metformin could still, though rarely, cause low blood sugar, and named diarrhoea, nausea and an upset stomach as its common side effects.

Why were some metformin products recalled in 2020?

Testing by FDA found N-nitrosodimethylamine (NDMA), a nitrosamine impurity, in certain lots of extended-release metformin. The agency announced those findings in May 2020, and by June it had recommended that five companies recall the products voluntarily, which they did. FDA's testing had not shown NDMA in immediate-release metformin, which it describes as the most commonly prescribed type. One more extended-release lot was recalled as late as January 2021.

Made of the same elements

Sources

  1. PubChem CID 4091, metformin
  2. IUPAC/CIAAW, Abridged Standard Atomic Weights 2024
  3. PubChem Laboratory Chemical Safety Summary for metformin (CID 4091)
  4. LiverTox (NIDDK and NLM), via PubChem CID 4091: LiverTox Summary for metformin
  5. US Food and Drug Administration, FDA Drug Safety Communication: FDA revises warnings regarding use of the diabetes medicine metformin in certain patients with reduced kidney function (2016) (archived 12 February 2026)
  6. US Food and Drug Administration, FDA Updates and Press Announcements on NDMA in Metformin
  7. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), Insulin, Medicines, & Other Diabetes Treatments
  8. National Cancer Institute, NCI Drug Dictionary: metformin hydrochloride
  9. Stephen Lower, Chem1 General Chemistry, §9.7 The Hybrid Orbital Model II (LibreTexts, CC BY 3.0)
  10. Stephen Lower, Chem1 General Chemistry, §10.3 Acid-Base Reactions à la Brønsted (LibreTexts, CC BY 3.0)