Which of the following effectively decreases blood glucose levels?

Insulin is the hormone that effectively decreases blood glucose levels. It is produced by the beta cells of the pancreas in response to elevated blood glucose levels, such as after eating a meal. Insulin facilitates the uptake of glucose into the body's cells, particularly in muscle and adipose (fat) tissues, where it can be utilized for energy or stored as glycogen. Additionally, insulin inhibits hepatic glucose production, further contributing to the reduction of glucose levels in the bloodstream.

The action of insulin is crucial for maintaining glucose homeostasis. In individuals with insulin resistance or diabetes, this process can be impaired, leading to elevated blood glucose levels. Understanding the role of insulin helps to clarify why it is the primary hormone involved in lowering blood glucose, distinguishing its function from other hormones like glucagon, adrenaline, and cortisol, which are more associated with raising blood glucose levels or responding to stress.