Biguanides

Biguanides lower blood sugar mainly by reducing glucose production in the liver and improving the body's response to insulin. Metformin, the only member in use, is the usual first-line drug for type 2 diabetes and rarely causes low blood sugar on its own. Nausea, diarrhea, and stomach upset are common at first and lessen when it is taken with food. Lactic acidosis is rare but serious, so kidney function is checked regularly and the drug is often paused around imaging studies that use iodinated contrast.

• MetforminKnown brand names include Glucophage, Glumetza, and Riomet.