Metformin

Glucophage® · Glumetza®(brand names vary by market)

First among diabetes drugs: effective, weight-neutral, and it does not cause hypoglycemia by itself.

Also: modified release

Mechanism

Reduces hepatic gluconeogenesis (AMPK-linked) and improves peripheral insulin sensitivity; no insulin release, hence no intrinsic hypoglycemia.

TabletModified release

GI tolerance

Start low, go slow, take with food; extended-release rescues many intolerant patients.

Renal function

Dose reduced then stopped as eGFR falls (commonly reduce <45, avoid <30); held during acute illness with dehydration ('sick day' drug).

Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.

Bioavailability: ~50-60%
Half-life: ~5-6 h
Elimination: renal: Excreted unchanged; accumulates exactly when kidneys fail

GI upset: nausea, diarrhea, metallic tastecommon
Vitamin B12 deficiency with long usecommon
Lactic acidosisseriousRare, almost always with renal failure, hypoxia, or contrast mishaps.

Contraindications

Precautions

HbA1c

Effectiveness · Every 3-6 months

eGFR

The dose and the safety gate · At least annually, more often near cutoffs

B12 periodically with long-term use

Deficiency is insidious and treatable

Take with meals; stomach upset usually fades over weeks.
Pause it when seriously unwell with vomiting, diarrhea, or dehydration, and restart when eating and drinking normally.
It does not cause low sugar on its own.

'Sick day medication list': metformin, RAAS blockers, diuretics, SGLT2 inhibitors. The ones to pause in dehydration.

Metformin product monograph (consult the current version for your market) (monograph)
Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)

Last reviewed 2026-08-15 · jurisdiction: global · drug information changes; verify against current references before practice use.

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