Glucagon is produced to maintain glucose levels in the bloodstream when fasting and to raise very low glucose levels.

What is glucagon?

Glucagon is a hormone that is involved in controlling blood sugar (glucose) levels. It is produced by the alpha cells, found in the islets of Langerhans, in the pancreas, from where it is released into the bloodstream. The glucagon-secreting alpha cells surround the insulin-secreting beta cells, which reflects the close relationship between the two hormones.

Glucagon’s role in the body is to prevent blood glucose levels dropping too low. To do this, it acts on the liver in several ways:

  • It stimulates the conversion of stored glycogen (stored in the liver) to glucose, which can be released into the bloodstream. This process is called glycogenolysis.
  • It promotes the production of glucose from amino acid molecules. This process is called gluconeogenesis.
  • It reduces glucose consumption by the liver so that as much glucose as possible can be secreted into the bloodstream to maintain blood glucose levels.

Glucagon also acts on adipose tissue to stimulate the breakdown of fat stores into the bloodstream.

Another rare effect of Glucagon, is its use as a therapy for beta blocker medication overdose.

How is glucagon controlled?  

Glucagon works along with the hormone insulin to control blood sugar levels and keep them within set levels. Glucagon is released to stop blood sugar levels dropping too low (hypoglycaemia), while insulin is released to stop blood sugar levels rising too high (hyperglycaemia). It is one of the ‘’anti-insulin’’ hormones. It works in totally opposite way to insulin.

The release of glucagon is stimulated by low blood glucose, protein-rich meals and adrenaline (another important hormone for combating low glucose). The release of glucagon is prevented by raised blood glucose and carbohydrate in meals, detected by cells in the pancreas.

In the longer-term, glucagon is crucial to the body’s response to lack of food. For example, it encourages the use of stored fat for energy in order to preserve the limited supply of glucose.

What happens if I have too much glucagon?

A rare tumour of the pancreas called a glucagonoma can secrete excessive quantities of glucagon. This can cause diabetes mellitus, weight loss, venous thrombosis and a characteristic skin rash.

What happens if I have too little glucagon?

Unusual cases of deficiency of glucagon secretion have been reported in babies. This results in severely low blood glucose which cannot be controlled without administering glucagon. 

Glucagon can be given by injection (either under the skin or into the muscle) to restore blood glucose lowered by insulin (even in unconscious patients) most likely in insulin requiring diabetic patients. It can increase glucose release from glycogen stores. Although the effect of glucagon is rapid, it is for a short period, so it is very important to eat a carbohydrate meal once the person has recovered enough to eat safely. This effect can be impaired/limited in individuals consuming large amounts of alcohol and those with liver disease due to insufficient glycogen stores.

Last reviewed: Sep 2021