Insulin is used when blood sugar levels are high, reports Mayo Clinic. The insulin helps glucose enter the tissues instead of remaining in the blood.
People with diabetes do not produce insulin or are unable to use insulin effectively, states American Family Physician. Insulin shots help diabetics control their blood sugar levels. When someone takes too much insulin, his blood sugar levels drop too low, a condition called hypoglycemia. Diabetics should keep candy or sweetened beverages around in case they take too much insulin and experience an insulin reaction. Most diabetics need at least two insulin shots per day, but some need three or four injections to keep their glucose levels under control.