Hypoglycemia is a condition characterized by an abnormally low level of blood sugar (glucose), your body's main energy source.

What is it?

  • Hypoglycaemia is a condition characterized by an abnormally low level of blood sugar (glucose), your body's main energy source.
  • Hypoglycaemia is commonly associated with diabetes. However, a variety of conditions, many of them rare, can cause low blood sugar in people without diabetes. Like fever, hypoglycaemia isn't a disease itself — it's an indicator of a health problem.
  • Immediate treatment of hypoglycemia involves quick steps to get your blood sugar level back into a normal range, either with high-sugar foods or medications. Long-term treatment requires identifying and treating the underlying cause of hypoglycemia.


Your brain needs a steady supply of sugar (glucose), for it neither stores nor manufactures its own energy supply.

If glucose levels become too low, as occurs with hypoglycaemia, it can have these effects on your brain:

  • Confusion, abnormal behavior or both, such as the inability to complete routine tasks
  • Visual disturbances, such as double vision and blurred vision
  • Seizures, though uncommon
  • Loss of consciousness, though uncommon

Hypoglycaemia may also cause these other signs and symptoms:

  • Heart palpitations
  • Tremor
  • Anxiety
  • Sweating
  • Hunger

These signs and symptoms aren't specific to hypoglycaemia. There may be other causes. Measurement of your blood sugar level at the time of these signs and symptoms is the only way to know for sure that hypoglycaemia is the cause.


Hypoglycaemia occurs when your blood sugar (glucose) level falls too low. There are several reasons why this may happen, the most common being a side effect of drugs used for the treatment of diabetes. But to understand how hypoglycaemia happens, it helps to know how your body normally regulates blood sugar production, absorption and storage.

Blood sugar regulation

During digestion, your body breaks down carbohydrates from foods — such as bread, rice, pasta, vegetables, fruit and milk products — into various sugar molecules. One of these sugar molecules is glucose, the main energy source for your body. Glucose is absorbed directly into your bloodstream after you eat, but it can't enter the cells of most of your tissues without the help of insulin — a hormone secreted by your pancreas.

When the level of glucose in your blood rises, it signals certain cells (beta cells) in your pancreas, located behind your stomach, to release insulin. The insulin, in turn, unlocks your cells so that glucose can enter and provide the fuel your cells need to function properly. Any extra glucose is stored in your liver and muscles in the form of glycogen. This process lowers the level of glucose in your bloodstream and prevents it from reaching dangerously high levels. As your blood sugar level returns to normal, so does the secretion of insulin from your pancreas.

If you haven't eaten for several hours and your blood sugar level drops, another hormone from your pancreas called glucagon signals your liver to break down the stored glycogen and release glucose back into your bloodstream. This keeps your blood sugar level within a normal range until you eat again.

Aside from your liver breaking down glycogen into glucose, your body also has the ability to manufacture glucose in a process called gluconeogenesis. This process occurs primarily in your liver, but also in your kidneys, and makes use of various substances that are precursors to glucose.

Possible causes, with diabetes

If you have diabetes, the effects of insulin on your body are drastically diminished, either because your pancreas doesn't produce enough of it (type 1 diabetes) or because your cells are less responsive to it (type 2 diabetes). As a result, glucose tends to build up in your bloodstream and may reach dangerously high levels. To correct this problem, you likely take insulin or other drugs designed to lower blood sugar levels.

If you take too much insulin relative to the amount of glucose in your bloodstream, it can cause your blood sugar level to drop too low, resulting in hypoglycemia. Hypoglycemia may also result if, after taking your diabetes medication, you don't eat as much as usual (ingesting less glucose) or you exercise more (using up more glucose) than you normally would. To prevent this from happening, it's likely that your doctor will work with you to find the optimum dosage that fits your regular eating and activity habits.

Possible causes, without diabetes

Hypoglycemia in people without diabetes is much less common. Causes may include the following:

  • Medications. Taking someone else's oral diabetes medication accidentally is a possible cause of hypoglycemia. Other medications may cause hypoglycaemia, especially in children or in people with kidney failure. One example is quinine, which is used to treat leg cramps as well as malaria.
  • Excessive alcohol consumption. Drinking heavily without eating can block your liver from releasing stored glucose into your bloodstream, causing hypoglycemia.
  • Some critical illnesses. Severe illnesses of the liver, such as severe hepatitis, can cause hypoglycemia. Disorders of the kidney, which can keep your body from properly excreting medications, can affect glucose levels due to a buildup of those medications. Long-term starvation, as may occur in the eating disorder anorexia nervosa, can result in the depletion of substances your body needs in gluconeogenesis, causing hypoglycaemia.
  • Tumors. A rare tumor of the pancreas (insulinoma) may cause overproduction of insulin, resulting in hypoglycemia. Other tumors may result in excessive production of insulin-like substances. Or, the tumors themselves may use up too much glucose. Enlargement of beta cells of the pancreas that produce insulin (nesidioblastosis) may result in excessive insulin release, causing hypoglycemia. People who've undergone gastric bypass surgery are at risk of this condition.
  • Endocrine deficiencies. Certain disorders of the adrenal glands and the pituitary gland can result in a deficiency of key hormones that regulate glucose production. Children with these disorders are more prone to hypoglycaemia than are adults.

Hypoglycaemia after meals

Most hypoglycemia occurs when you haven't eaten (when you're in a fasting state), but that's not always the case. Sometimes, hypoglycemia occurs after meals because the body produces more insulin than is needed. This type of hypoglycemia, called reactive or postprandial hypoglycemia, is typical in people who have had gastric bypass surgery.


If you ignore the symptoms of hypoglycemia too long, you may lose consciousness. That's because your brain needs glucose to function.

Recognize the signs and symptoms of hypoglycemia early because untreated, hypoglycemia can lead to:

  • Seizure
  • Loss of consciousness
  • Death

On the other hand, if you have diabetes, be careful not to overtreat your low blood sugar. If you do, you may cause your blood sugar level to rise too high. This, too, can be dangerous and may cause damage to your nerves, blood vessels and various organs.


To diagnose hypoglycemia, your doctor will use Whipple's triad, a diagnostic approach named after the American surgeon Allen Whipple. Whipple's triad includes the following factors:

Signs and symptoms of hypoglycaemia. You may not exhibit signs and symptoms of hypoglycemia during your initial visit with your doctor. In this case, your doctor may have you fast overnight. This will allow hypoglycemic symptoms to occur so that he or she can make a diagnosis. It's also possible that you'll need to undergo an extended fast in a hospital setting. Or, if your symptoms occur after a meal, your doctor will want to test your glucose levels after a meal.

  • Documentation of low blood glucose when the signs and symptoms occur. Your doctor will draw a sample of your blood to be analyzed in the laboratory.
  • Disappearance of the signs and symptoms. The third part of the diagnostic triad involves whether your signs and symptoms go away when blood glucose levels are raised.

In addition, your doctor will likely conduct a physical examination and review your medical history.