Information last reviewed: May 2026 — for educational purposes only.
What Is Metformin?
Metformin (brand name Glucophage) is the most widely prescribed oral antidiabetic medication in the world. It belongs to the biguanide class and works primarily by inhibiting hepatic gluconeogenesis (glucose production by the liver), which accounts for most of its glucose-lowering effect. It also improves peripheral insulin sensitivity and slightly reduces intestinal glucose absorption. Unlike sulfonylureas or insulin, metformin does not cause hypoglycaemia and is associated with modest weight loss or weight neutrality, and has well-established cardiovascular safety data (UKPDS trial).
Prescription (Rx) Status
Metformin is prescription-only in the US. Immediate-release (IR) and extended-release (XR/ER) forms are available as inexpensive generics. In 2020, the FDA recalled certain metformin ER formulations due to elevated NDMA levels; most extended-release products remain on the market. Metformin is contraindicated in patients with significant renal impairment (eGFR < 30 mL/min) due to risk of lactic acidosis, a rare but serious complication.
Uses of Metformin
Primary indication: type 2 diabetes mellitus, as first-line monotherapy or in combination. Off-label uses include: polycystic ovary syndrome (PCOS) — improves menstrual regularity and reduces androgen levels; prediabetes — delays or prevents progression to T2DM; and gestational diabetes (some guidelines). Metformin has also been studied for longevity and cancer risk reduction but has not been approved for these indications.
Tablet Strengths
Metformin IR oral tablets: 500 mg, 850 mg, and 1000 mg. Extended-release (XR/ER): 500 mg, 750 mg, and 1000 mg. Usual starting dose: 500 mg twice daily or 850 mg once daily with meals, titrated slowly. Maximum dose: 2550 mg/day (IR) or 2000 mg/day (ER). Take with food to reduce GI side effects.
Price
Metformin IR is one of the cheapest prescription drugs available. A 30-day supply of 500 mg tablets costs approximately $4–$10 at most pharmacies. Many discount programmes (GoodRx, $4 generics) make it essentially free for many patients.
Frequently Asked Questions
Q: Does metformin cause GI side effects?
A: Yes — nausea, diarrhoea, and stomach upset are common, especially initially. Taking it with food and starting at a low dose and titrating slowly reduces GI intolerance. ER formulations cause fewer GI side effects.
Q: Does metformin deplete B12?
A: Yes — long-term use is associated with reduced vitamin B12 absorption. Periodic monitoring of B12 levels is recommended, especially in patients with neuropathy.
Q: Can metformin be used for weight loss?
A: It is weight-neutral to mildly weight-reducing and is often prescribed off-label for weight management in insulin-resistant individuals, though it is not FDA-approved for this indication.
Disclaimer: This page is for informational purposes only and does not constitute medical advice. Metformin requires a valid prescription. Always consult a qualified healthcare professional. See our full disclaimer.