Which is a mechanism of action of metformin?

• A. Stimulates insulin release from pancreatic beta cells
• B. Inhibits glucose reabsorption in the kidneys
• C. Inhibits liver glucose production
• D. Increases breakdown of glycogen in liver

Answer: (C)

Metformin’s primary way of lowering blood glucose is by shutting down glucose production in the liver. It activates AMPK in liver cells, which decreases gluconeogenesis and thus reduces hepatic glucose output. This effect lowers fasting and post-meal glucose levels without relying on stimulating insulin release. That’s why the mechanism described as inhibiting liver glucose production fits metformin best. It’s not about prompting insulin secretion, which is how drugs like sulfonylureas work; it’s not about blocking kidney glucose reabsorption, which is the action of SGLT2 inhibitors; and it doesn’t increase glycogen breakdown in the liver (that would raise glucose, not lower it).