Insulin is the hormone responsible for lowering blood glucose levels by facilitating the uptake of glucose into cells, particularly muscle and adipose tissue. It promotes the storage of glucose as glycogen in the liver and inhibits gluconeogenesis. These actions collectively reduce blood sugar concentrations. In contrast, other hormones like glucagon and cortisol increase blood glucose. Therefore, insulin is critical for maintaining glucose homeostasis and preventing hyperglycemia.

Reference: Principles of Internal Medicine, Harrison, 20th Edition.