Which biguanide is first-line for type 2 diabetes and what is its main action?

• A. Sulfonylurea; stimulates insulin release.
• B. Metformin; decreases hepatic gluconeogenesis and improves insulin sensitivity.
• C. Thiazolidinedione; increases insulin sensitivity.
• D. Alpha-glucosidase inhibitor; delays carbohydrate absorption.

Answer: (B)