Metformin is first-line therapy for glycemic control in people with type 2 diabetes. It is effective, safe, inexpensive, and widely available, and may reduce cardiovascular events and mortality.1 However, metformin is cleared by the kidneys and it has historically been contraindicated in patients with chronic kidney disease (CKD) because of concerns of lactic acidosis with drug accumulation. A series of observational studies during the early 2000s demonstrated the rarity of this adverse event across metformin users with CKD G3 (estimated glomerular filtration rate [eGFR]=30-59mL/min/1.73m2),2-5 and this led in 2016 to a label change by the US Food and Drug Administration and European medicine agency expanding the indication of metformin use to CKD G3.