Buformin is a biguanide derivative with antihyperglycemic activity. It delays absorption of glucose from the gastrointestinal tract, increases insulin sensitivity and glucose utilization in peripheral cells, and inhibits hepatic gluconeogenesis. It can also deactivate the glycolytic pathway by suppressing glyceraldehyde 3-phosphate dehydrogenase gene expression, which can lead to lactic acidosis. Biguanides, such as buformin, are reported to inhibit the mitochondrial respiratory complex I by inhibiting ubiquinone reduction and by stimulating reactive oxygen species production via the complex I flavin. Some biguanides, including buformin, can also inhibit the mitochondrial ATP synthase. Buformin has also been examined for antitumor activity due to its ability to disrupt the unfolded protein response transcription program during glucose deprivation, which induces cell death in glucose-deprived tumor cells.