- The hormone that plays the main role in reducing blood glucose levels in the body is Insulin.
- Insulin is produced by the beta cells of the pancreas and facilitates the uptake of glucose by cells, especially muscle and adipose tissue, for energy production or storage as glycogen.
- It effectively lowers blood glucose levels by promoting glucose utilization and inhibiting glucose production in the liver.

- In contrast, Glucagon (Option 1) increases blood glucose levels by stimulating glycogen breakdown and glucose production in the liver.
- Cortisol (Option 3) and Epinephrine (Option 4) also raise blood glucose levels indirectly by promoting gluconeogenesis and glycogenolysis during stress or fasting.

Therefore, insulin is the primary hormone responsible for decreasing blood glucose concentration and maintaining glucose homeostasis in the body.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th Edition, Chapter 76: Pancreatic Hormones and Diabetes Mellitus