Metformin is the most widely prescribed blood-sugar-lowering pill in the world. It belongs to a class of drugs called biguanides, and it is the only biguanide approved for use in the United States.

The American Diabetes Association (ADA) recommends metformin as the first-line oral treatment for people newly diagnosed with type 2 diabetes, unless they have some contraindication or other reason they can’t take it.

Metformin is sold as a generic and also under the brand names Glucophage, Glucophage XR, Fortamet, Riomet, and Glumetza.

History of Metformin

Metformin was first used to treat diabetes in France in the late 1950s. However, it wasn’t introduced in the United States until 1994.

The Food and Drug Administration (FDA) held off on approving metformin because of a fear of lactic acidosis (which causes lactic acid to build up in the bloodstream faster than it can be removed), a dangerous side effect of some members of the biguanide class of drugs.

However, while every prescription of metformin still carries a warning about lactic acidosis, actual cases of lactic acidosis associated with metformin use are exceedingly rare.

Regular metformin is now approved for use in adults and children as young as age 10, while extended-release metformin is approved for people ages 17 and older.

How Metformin Works

No one knows exactly how metformin lowers blood sugar, although the leading theory is that it limits glucose production by the liver and increases insulin sensitivity, so that more glucose is taken up by muscle, fat, liver, and other types of cells.

When used alone, metformin lowers A1C levels (a blood sugar measurement) by about one percent.

In addition to lowering blood sugar, metformin has been shown to reduce the risk of heart attack. It can also increase fertility in women with polycystic ovarian syndrome (PCOS).

Metformin Dosage

Regular metformin is sold in tablets of 500 milligrams (mg), 850 mg, and 1,000 mg. Extended-release metformin is sold in tablets of 500 mg, 750 mg, and 1,000 mg.

The brand Riomet is a liquid formulation of metformin.

There is no fixed dosing regimen for metformin, although it’s common to start with a low dose and increase it over several weeks to minimize side effects while reaching an effective dose.

Metformin is generally taken with meals, and larger daily doses may be divided among two or three meals.

The maximum recommended daily dose of metformin is 2,550 mg for adults and 2,000 mg for children ages 10-16.

Side Effects of Metformin

The most common negative side effects of metformin are gastrointestinal in nature and may include stomach irritation and diarrhea.

These side effects can often be minimized by starting with a low dose and raising the dosage gradually. Another option is to try an extended-release version of the drug, which may be better tolerated.

Another potential side effect of metformin is vitamin B12 deficiency. About five percent of people who take metformin develop a vitamin B12 deficiency, and it’s more common in people who have taken the drug for many years.

Vitamin B12 deficiency is treated with supplementation, either via injections or oral supplements.

Metformin rarely causes hypoglycemia (low blood sugar) when used alone as treatment for type 2 diabetes.