Short answer: Metformin has a half-life of about 6.2 hours. People vary, so treat these as estimates.
Metformin is a biguanide, a blood-sugar-lowering drug taken by mouth for type 2 diabetes. It is sold as generic immediate-release and extended-release tablets; FDA lists the original brand, Glucophage, as discontinued.
Also known as: Glucophage.
Generic immediate-release metformin tablets come in 500 mg, 850 mg and 1,000 mg strengths. Extended-release tablets are also sold.
The FDA label approves metformin, with diet and exercise, to improve blood sugar control in adults and children 10 and older with type 2 diabetes. For adults the immediate-release label dose starts at 500 mg twice a day or 850 mg once a day with meals, raised by 500 mg a week or 850 mg every 2 weeks, up to 2,550 mg a day in divided doses. Other uses, such as for weight or aging, are off-label.
The label carries a boxed warning for lactic acidosis, a rare but sometimes fatal build-up of lactic acid. Risk is higher with kidney impairment, age 65 or over, heavy drinking, liver impairment, contrast X-ray studies and surgery. Kidney function (eGFR) is checked before starting: metformin is not used below 30 and not started between 30 and 45. Metformin can lower vitamin B12, so the label suggests checking B12 every 2 to 3 years.
The FDA metformin label gives a plasma elimination half-life of about 6.2 hours, with about 90% of the absorbed drug cleared by the kidneys within 24 hours. In whole blood the half-life is about 17.6 hours. Steady state is reached in 24 to 48 hours, and bioavailability of a 500 mg tablet is about 50% to 60%. Food lowers the peak by about 40% and delays it by about 35 minutes; the label gives no typical time to peak, so we do not list one.
Numbers shown are taken from the source above. Half-life varies from person to person.
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