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Medically reviewed by Last updated on Dec 15, 2022.

What is Hypoglycemia?

Harvard Health Publishing

Hypoglycemia is an abnormally low level of blood sugar (blood glucose). Hypoglycemia triggers the release of body hormones, such as epinephrine (adrenaline) and norepinephrine (noradrenaline), which serve to raise the low sugar level. The release of these hormones causes the early symptoms of hypoglycemia such as tremor, sweating, rapid heartbeat, and anxiety. Because the brain depends on blood sugar as its primary source of energy, if untreated hypoglycemia may interfere with the brain's ability to function properly, resulting in blurred vision, difficulty concentrating, and even loss of consciousness and convulsions (seizures).

Hypoglycemia is most common in people with diabetes who are treated with specific medications. Hypoglycemia occurs because of too high a dose of insulin or one of the sulfonylureas (glyburide, glipizide and others), or a change in diet or exercise without adjusting glucose-lowering medications. Insulin and exercise both lower blood sugar and food with carbohydrate raises it.

Hypoglycemia can occur, although rarely, in people who do not have diabetes. When it does occur outside of diabetes, hypoglycemia can be caused by a variety of medical problems. A partial list includes:

  • gastrointestinal surgery, such as weight loss surgery, in which part of the stomach may be removed or "bypassed." Such procedures can disrupt the normal relationships between digestion and insulin release. "Nissen" surgeries for treatment of gastroesophageal reflux can also result in episodes of hypoglycemia.
  • a pancreatic tumor, called an insulinoma, that abnormally secretes insulin
  • a deficiency of growth hormone from the pituitary gland or of cortisol from the adrenal glands. Both of these hormones help to keep blood sugars normal
  • alcohol
  • overdose of aspirin
  • severe liver disease
  • use of insulin by someone who does not have diabetes
  • rare cancers that secrete an insulin-like substance
  • rarely, an enzyme defect. Examples of enzymes that help keep blood sugar normal are glucose-6-phosphatase, liver phosphorylase, and pyruvate carboxylase.


Hypoglycemia can cause:

  • Symptoms related to the release of epinephrine and norepinephrine — Sweating, tremors (feeling shaky), rapid heartbeat, anxiety, hunger
  • Symptoms related to the brain "starving" for sugar Headache, dizziness, blurred vision, difficulty concentrating, poor coordination, confusion, weakness or fainting, tingling sensations in the lips or hands, confused speech, abnormal behavior, convulsions, loss of consciousness, coma.


If a person with diabetes has severe hypoglycemia, he or she may not be able to answer the doctor's questions because of confusion or unconsciousness. In this case, a family member or close friend will need to describe the patient's medical history and insulin regimen.

To help ensure effective emergency treatment, all people with diabetes treated with insulin or a sulfonylurea should consider wearing a medical alert bracelet or necklace. This potentially lifesaving jewelry will identify the patient as having diabetes, especially when the patient is far from home or traveling alone.

Family members or friends of a person with diabetes should learn how to bring a patient out of severe hypoglycemia by giving the person orange juice or another carbohydrate, or by giving an injection of the drug glucagon, which can raise blood sugar.

If a person with diabetes can answer questions appropriately, the doctor will want to know the names and doses of all medications, as well as recent food intake and exercise schedule. If the patient has been self-monitoring blood sugar with a glucometer (a hand-held device to measure glucose levels in blood from a finger prick) or with continuous glucose monitoring, the doctor will review the most recent blood sugar readings to confirm low blood sugar and to check for a pattern of hypoglycemia related to medication schedule, diet, or exercise.

In people who do not have diabetes, the doctor will review current medications and ask about any history of gastrointestinal surgery (especially involving the stomach), liver disease, and the circumstances surrounding the epsodes. Patients should describe their symptoms and when they occur — whether they occur before or after meals, during sleeping, or after exercise.

In a person with diabetes, the diagnosis of hypoglycemia is based on symptoms and blood sugar readings. In most cases, no further testing is necessary.

In a person who is not diabetic, the ideal time for diagnostic testing is during an episode of symptoms. At that time, blood can be drawn to measure levels of glucose, and the patient's reactions to glucose intake can be tested. If these measures confirm the diagnosis of hypoglycemia, blood can be sent to a laboratory to measure insulin levels.

In a person who is not diabetic, the ideal time for diagnostic testing is during an episode of symptoms. At that time, blood can be drawn to measure levels of glucose and insulin if an insulinoma is suspected. Other hormones, such as cortisol and thyroid levels, may also be measured. If the patient has no symptoms at the time of evaluation, the doctor may ask him or her to measure his or her blood glucose when hypoglycemic symptoms occur.

If an insulinoma is suspected, the doctor may order a supervised 48-hour fast. During that period, blood levels of glucose and insulin will be measured when symptoms occur. A blood glucose level of less than 60 milligrams per deciliter at the time of symptoms and with a measurable level of insulin strongly suggests the person has an insulinoma. Accidental use of insulin or another diabetic drug may also cause hypoglycemia.

If a person develops symptoms of hypoglycemia only after eating, the doctor may ask him or her to self-monitor blood sugar with a glucometer at the time the symptoms occur.

Expected duration

An episode of hypoglycemia in a patient treated with short-acting insulin and which is precipitated by exercise or by relatively too much insulin usually can be stopped within minutes by eating or drinking a food or beverage that contains sugar (sugar tablets, candy, orange juice, non-diet soda). Hypoglycemia caused by sulfonylurea or long-acting insulin can last longer and can even recur after initial treatment. In this circumstance, a longer-lasting carbohydrate (for example, bread or a muffin) should be eaten after the rapid carbohydrate.

People with diabetes remain at risk for episodes of hypoglycemia throughout life because they need medications that lower blood sugar. Hypoglycemic episodes at night are particularly dangerous because the person often sleeps through part of the time that their blood sugar is low, treating the sugar level less quickly. Over time, repeated severe episodes, such as with loss of consciousness or seizures, can lead to impaired brain function.

About 85% of patients with an insulinoma will be cured of hypoglycemia once the insulin-secreting tumor is removed.

Many people without diabetes who have symptoms that seem like signs of low blood sugar do not truly have low sugar levels. Instead, the symptoms are caused by something other than low blood glucose, such as anxiety.


In people taking insulin or sulfonylureas, delayed or smaller meals than usual or increased exercise can lead to hypoglycemia. Therefore, meal timing and size should be kept as consistent as possible. In addition, drinking alcohol can lead to an episode of hypoglycemia. Patients with diabetes should discuss with their doctors how much alcohol, if any, they can drink safely. Alcohol can cause serious episodes of hypoglycemia even when insulin was taken hours before. People with diabetes should be very aware of this possible problem if they drink.

People with diabetes treated with insulin should always have ready access to a supply of rapidly absorbable sugar to treat unexpected episodes of hypoglycemia. Supplies may include candy, sugar tablets, and sugar paste in a tube. A glucagon kit should be kept at home.  Glucagon may be given by injection or nasally by a knowledgeable family member or friend if a hypoglycemic patient is unconscious and cannot safely take sugar by mouth. For diabetic children, emergency supplies can be kept in the school nurse's office.

Any person at risk of hypoglycemic episodes can help to avoid delays in treating attacks by learning about his or her condition and sharing this knowledge with friends and family members. The risk for hypoglycemia is lower if you eat at regular times during the day, never skip meals, and maintain a consistent exercise level.

Like people with diabetes, nondiabetic people with hypoglycemia should always have ready access to a source of sugar. In rare circumstances, a doctor may prescribe medications to reduce the risk of hypoglycemia, and a glucagon emergency kit for nondiabetic people who have a history of becoming disoriented or losing consciousness from hypoglycemia.


If a conscious person is having symptoms of hypoglycemia, the symptoms usually go away within 5-15 minutes if the person eats or drinks something sweet (3 sugar tablets, 4-5 Life Savers candies, or 4-6 ounces of juice or non-diet soda). An unconscious patient can be treated with an immediate injection of glucagon or with intravenous glucose infusions by EMTs or in a hospital.

People with diabetes who have hypoglycemic episodes may need to adjust their medications, especially the insulin dose, and change their diet or their exercise habits.

People with longstanding diabetes may stop experiencing the usual early warning symptoms (the tremors, sweating and fast heart rate) of hypoglycemia. This is called hypoglycemic unawareness. It can be very serious because the person may not know to seek treatment.

If you and your doctor identify that you are unaware when you have low blood sugars, your dose of insulin or other diabetes medicines will probably need to be reduced. You will need to check your blood sugar more often, and continuous glucose monitors that alarm when blood sugars are low may be helpful. Your insulin dose will likely need frequent adjustments to maintain reasonable blood sugars with less risk of hypoglycemia.

An insulinoma is treated with surgery to remove the tumor. Hypoglycemia caused by problems with the adrenal or pituitary glands is treated by replacing the missing hormones with medication.

Nondiabetic people with hypoglycemic symptoms following meals are often treated by modifying their diet. They usually need to eat frequent, small meals and avoid fasting.

Treatment options

The following list of medications are in some way related to or used in the treatment of this condition.

View more treatment options

When to call a professional

Call for emergency medical assistance whenever anyone is unconscious or disoriented enough so that they cannot safely be treated with oral therapy. Severe insulin reactions can be fatal, so it is important to seek treatment immediately.

People with diabetes should contact their doctors promptly if they experience frequent episodes of hypoglycemia. They may need to adjust their daily doses of medications, meal plans, and/or exercise program.

Nondiabetic people who experience symptoms of hypoglycemia should contact their doctors for evaluation of the problem.


In people with diabetes, the outlook is excellent if they follow their prescribed medication dosage, recommended diet, and exercise guidelines.

Most patients with insulinomas can have them removed successfully by surgery. However, in a small percentage of these patients, the insulinoma cannot be completely removed. These patients may still suffer from hypoglycemia after surgery.

Most patients with other forms of hypoglycemia can be treated successfully with changes in diet.

Additional info

National Institute of Diabetes & Digestive & Kidney Disorders

American Diabetes Association

Learn more about Hypoglycemia

Treatment options

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.