Final answer:
Insulin is administered subcutaneously to slow down the absorption rate, which is critical for its effectiveness in regulating blood glucose levels.
Step-by-step explanation:
The primary reason insulin is injected via the subcutaneous route is because medication absorption is slower from subcutaneous tissue, which is an important factor in the effectiveness of insulin therapy. When a drug such as insulin is not efficiently absorbed in the gastrointestinal tract, or when rapid absorption is not desired, administration by a parenteral route such as subcutaneous injection is preferred. Insulin helps regulate blood glucose levels by facilitating the uptake of glucose into body cells, particularly after consuming a meal high in glucose, thereby decreasing blood glucose levels.