What happens to the blood sugar levels of a diabetic if he injects too much insulin?

Answer 1

This will result too much glucose being taken up by storage cells (in the liver) and so not enough for the cell to make energy to function properly. As a result tissue may receive damage and the brain may start to malfunction.

Answer 2

The excess insulin causes the body's cells to accept too much glucose from the blood, faster than it can be replenished from food. This means that the blood will shortly contain too little sugar to sustain the brain's constant need for fuel.

This condition, with too little sugar in the blood to sustain the brain, is called Hypoglycemia, and it leads quickly to irritability, stupor, unconsciousness, and then if untreated, death by brain insult.

Fortunately it's extremely easy to treat if detected -- simply eating sugar or corn syrup (or if the victim is unconscious, smearing syrup on any mucous membrane, like gums) is generally enough to quickly raise blood sugar. If the insulin overdose was large, continual treatment and further doses of food and sugar will be required until most of the insulin is used up.

An overdose of insulin may not lead to hypoglycemia in some cases. If the body detects dropping blood sugar in time, it may signal the liver to release large amounts of stored glycogen from the liver, which fills the bloodstream with glucose. This saves the victim from hypoglycemic shock but can easily induce the opposite -- hyperglycemia (too much blood sugar). This "rebound" effect was first documented by Dr. Michael Somogyi in 1938 and is known as "Somogyi's phenomenon".