The "3-hour rule" is a common clinical guideline used by diabetics and their healthcare providers to manage insulin dosing and blood glucose safety. It generally dictates that insulin users should wait at least three hours after a corrective dose of rapid-acting insulin before administering an additional dose, unless specific medical guidance suggests otherwise. This rule is designed to prevent "insulin stacking," a dangerous phenomenon where multiple overlapping doses of insulin act concurrently, which can lead to severe hypoglycemia (dangerously low blood sugar). Because rapid-acting insulin has a specific physiological "tail" or duration of action, the three-hour buffer provides a safety window to observe how the first dose affects glucose levels before adding more, thereby minimizing the risk of rapid, unpredictable crashes that can lead to medical emergencies. It is a fundamental practice in safe, self-managed diabetes care regimens.