Hypoglycemia (Low Blood Sugar): Symptoms, Causes, Treatment and Prevention

Hypoglycemia, also called low blood glucose or low blood sugar, happens when the amount of glucose in the blood falls below a healthy level.

It is particularly common in people with diabetes who use insulin or certain other glucose-lowering medicines.

For many people with diabetes, a blood glucose level below 70 mg/dL (3.9 mmol/L) is considered low and requires action.

Hypoglycemia can develop quickly.

Mild episodes can usually be treated effectively, but severe hypoglycemia can cause:

• confusion,
• seizures,
• unconsciousness,
• coma,
• and, in extreme circumstances, death.

Knowing the warning signs and how to respond promptly is therefore extremely important.

Is Hypoglycemia the Same as “Insulin Shock”?

The old version of this article describes hypoglycemia as “insulin shock.”

That term is outdated and can be misleading.

Hypoglycemia is the appropriate medical term.

Although excessive insulin can cause hypoglycemia, not every episode is caused by insulin, and hypoglycemia can occasionally occur in people who do not have diabetes.

What Is a Normal Blood Sugar Level?

Blood glucose changes throughout the day according to:

• meals,
• physical activity,
• medicines,
• hormones,
• illness,
• and other factors.

For most people with diabetes, a glucose level below 70 mg/dL (3.9 mmol/L) is considered hypoglycemia.

However, individual glucose targets can differ.

People with diabetes should know the target range recommended by their healthcare team.

Levels of Hypoglycemia

Modern diabetes guidance divides hypoglycemia into clinically useful levels.

Level 1 Hypoglycemia

Blood glucose:

Below 70 mg/dL (3.9 mmol/L) but at least 54 mg/dL (3.0 mmol/L).

This is an important warning level.

Action should be taken to prevent glucose from falling further.

Level 2 Hypoglycemia

Blood glucose:

Below 54 mg/dL (3.0 mmol/L).

This is clinically significant hypoglycemia and requires immediate treatment.

Level 3 — Severe Hypoglycemia

Severe hypoglycemia is defined by the person's condition rather than simply a glucose number.

It means the person's thinking or physical functioning has become so impaired that they need another person's help to recover.

A person may:

• become severely confused,
• be unable to swallow safely,
• have a seizure,
• or lose consciousness.

This is an emergency.

What Causes Hypoglycemia in People With Diabetes?

Diabetes treatment is the most common setting in which hypoglycemia occurs.

Several factors can cause glucose to fall too low.

1. Too Much Insulin

Taking more insulin than the body needs can cause blood glucose to fall.

This may occur because of:

• an incorrect dose,
• changes in food intake,
• unexpected exercise,
• changes in insulin requirements,
• or errors in timing.

Never deliberately change an insulin dose without understanding how the change affects your diabetes management.

2. Certain Diabetes Medicines

Not every diabetes medicine commonly causes hypoglycemia.

The risk is particularly associated with:

• insulin,
• sulfonylureas,
• and meglitinides.

Many other modern diabetes medicines have a relatively low risk of causing hypoglycemia when used alone, although risk can change when medicines are combined.

Ask your healthcare professional whether your medication can cause low blood glucose.

3. Skipping or Delaying Meals

If you take insulin or another medicine that can lower glucose, missing or substantially delaying a meal can cause hypoglycemia.

Eating fewer carbohydrates than expected can have a similar effect.

The relationship between:

• medication,
• carbohydrate intake,
• and meal timing

is especially important for people using mealtime insulin.

4. Physical Activity

Exercise generally benefits health and diabetes management, but physical activity can lower blood glucose.

The effect may continue for hours after exercise.

The answer is not to avoid exercise.

Instead, people at risk of hypoglycemia may need to:

• check glucose around exercise,
• adjust carbohydrate intake,
• adjust medication when professionally advised,
• and learn how their individual glucose responds to different activities.

5. Alcohol

Alcohol can increase the risk of hypoglycemia, particularly when consumed without enough food.

The liver normally helps maintain blood glucose by releasing stored glucose.

Alcohol can interfere with this process.

Hypoglycemia related to alcohol may also occur several hours after drinking.

Alcohol can additionally make the symptoms of hypoglycemia more difficult to recognize.

People taking glucose-lowering medicines should discuss alcohol safety with their healthcare professional.

6. Illness

Illness can affect glucose in different ways.

Some illnesses raise blood glucose, while others can contribute to hypoglycemia—particularly when a person:

• cannot eat normally,
• is vomiting,
• has diarrhoea,
• or continues taking glucose-lowering medication despite substantially reduced food intake.

People with diabetes should have an individualized sick-day plan.

Can People Without Diabetes Develop Hypoglycemia?

Yes, but true hypoglycemia is much less common in people who do not have diabetes.

Possible causes include:

• certain medicines,
• prolonged fasting or severe malnutrition,
• excessive alcohol consumption,
• severe liver disease,
• kidney disease,
• serious infection or critical illness,
• certain hormone deficiencies,
• and rare insulin-producing tumours.

Some people may also experience hypoglycemia after eating, known as postprandial or reactive hypoglycemia.

Repeated symptoms in someone without diabetes should be professionally investigated rather than treated indefinitely with sweets without determining the cause.

What Are the Symptoms of Hypoglycemia?

Symptoms can appear quickly and vary considerably between people.

Early symptoms may include:

• shaking or trembling,
• sweating,
• hunger,
• dizziness,
• light-headedness,
• fast heartbeat,
• anxiety or nervousness,
• irritability,
• headache,
• weakness,
• and tiredness.

As glucose falls further, the brain may not receive enough glucose to function normally.

Brain-Related Symptoms

Low glucose affecting the brain can cause:

• difficulty concentrating,
• confusion,
• blurred vision,
• difficulty speaking,
• unusual behaviour,
• poor coordination,
• difficulty walking,
• extreme drowsiness,
• seizures,
• and loss of consciousness.

These symptoms can become dangerous very quickly.

Can Hypoglycemia Look Like Drunkenness?

Yes.

Severe low blood glucose can cause:

• slurred speech,
• confusion,
• poor coordination,
• unusual behaviour,
• and difficulty walking.

These symptoms may sometimes be mistaken for intoxication.

Someone with diabetes behaving unusually should not simply be assumed to be drunk.

Check their glucose when possible and respond appropriately.

What Is Hypoglycemia Unawareness?

Normally, falling blood glucose triggers warning symptoms such as:

• sweating,
• shaking,
• hunger,
• or a rapid heartbeat.

Some people gradually lose these warning signals.

This is called impaired awareness of hypoglycemia, often referred to as hypoglycemia unawareness.

The person may not realize their glucose is low until their brain function is already significantly affected.

It is more likely in people who:

• have had diabetes for many years,
• experience frequent episodes of hypoglycemia,
• or have certain other risk factors.

This increases the risk of severe hypoglycemia.

People experiencing reduced awareness should discuss it with their diabetes healthcare team.

Can Hypoglycemia Happen During Sleep?

Yes.

This is called nocturnal hypoglycemia.

Possible signs include:

• sweating during sleep,
• damp nightclothes or bedding,
• nightmares,
• restless sleep,
• waking with a headache,
• or feeling unusually tired, confused or irritable after waking.

Some people sleep through an episode without recognizing it.

Continuous glucose monitoring can be particularly helpful for people at risk because some systems can sound an alarm when glucose is falling or has become low.

How Do You Know Whether Your Blood Sugar Is Low?

When possible, check your glucose using:

• a blood glucose meter,
• or a continuous glucose monitor (CGM).

If you have diabetes and develop typical hypoglycemia symptoms but cannot immediately check your glucose, follow the emergency plan previously agreed with your healthcare team.

Do not delay necessary treatment when significant hypoglycemia is strongly suspected.

How Is Mild to Moderate Hypoglycemia Treated?

A widely used approach for an alert person who can swallow safely is the 15-15 rule.

The 15-15 Rule

If your blood glucose is below 70 mg/dL (3.9 mmol/L):

Step 1: Consume approximately 15 grams of fast-acting carbohydrate.

Step 2: Wait 15 minutes.

Step 3: Check your blood glucose again.

If it remains below 70 mg/dL, consume another approximately 15 grams of fast-acting carbohydrate.

Wait another 15 minutes and check again.

Repeat until glucose has returned to an appropriate range.

Individual treatment instructions may differ, particularly for young children.

What Contains About 15 Grams of Fast-Acting Carbohydrate?

Examples can include:

• 3–4 glucose tablets, depending on the product,
• one dose of glucose gel according to its label,
• approximately 120 mL (4 fluid ounces) of fruit juice,
• approximately 120 mL (4 fluid ounces) of regular non-diet soft drink,
• or about 1 tablespoon of sugar or honey.

Check product labels because carbohydrate amounts vary.

Once glucose has recovered, you may need an appropriate snack or meal depending on when you are next due to eat and your individualized treatment plan.

Why Isn't Chocolate the Best First Treatment?

Chocolate contains sugar, but it also contains substantial fat.

Fat can slow the absorption of carbohydrate.

When glucose needs to rise quickly, fast-acting carbohydrate such as glucose tablets, glucose gel or an appropriate sugary drink is generally preferable.

Chocolate or high-fat baked foods should therefore not usually be the first choice for treating an acute low.

What Should You Do for Severe Hypoglycemia?

Severe hypoglycemia requires immediate action.

A person may:

• be unable to swallow,
• become severely confused,
• have a seizure,
• or become unconscious.

Do not give food, sweets or drinks by mouth to someone who is unconscious or unable to swallow safely.

They could choke.

What Is Glucagon?

Glucagon is a hormone that raises blood glucose.

Emergency glucagon can be prescribed for people at risk of severe hypoglycemia.

Depending on the country and product, glucagon may be available as:

• an injection,
• a pre-filled device,
• an autoinjector,
• or a nasal preparation.

Family members, friends, caregivers and other appropriate people should know:

• where the glucagon is kept,
• when to use it,
• and how to administer the specific product.

After glucagon is given for severe hypoglycemia, seek emergency medical assistance according to local guidance.

What If Glucagon Is Not Available?

If someone with suspected severe hypoglycemia is unconscious, having a seizure or cannot safely swallow:

• contact your local emergency medical service immediately,
• place the person in a safe position,
• protect them from injury,
• and do not put food or drink into their mouth.

Follow the instructions of emergency professionals.

What Should You Do After Glucagon?

Once the person is awake and able to swallow safely, fast-acting carbohydrate may be needed, followed by longer-lasting carbohydrate or a meal according to professional instructions.

Emergency medical assessment is particularly important when:

• recovery is incomplete,
• symptoms return,
• the cause is uncertain,
• or severe hypoglycemia occurred unexpectedly.

Can Hypoglycemia Cause Seizures?

Yes.

Very low blood glucose can interfere with normal brain function and cause a seizure.

A hypoglycemic seizure is an emergency.

Do not put food, drink or objects into the person's mouth during a seizure.

Protect them from injury and seek emergency medical assistance.

Can Hypoglycemia Cause Coma?

Yes.

Severe and prolonged hypoglycemia can cause loss of consciousness and coma.

Although most episodes are successfully treated, untreated severe hypoglycemia can be life-threatening.

This is why rapid recognition and treatment are so important.

Can Hypoglycemia Be Prevented?

Not every episode can be prevented, but the risk can often be substantially reduced.

Know Your Medicines

Understand whether your diabetes medicines can cause hypoglycemia.

Take medicines according to your treatment plan.

Do not independently reduce, increase or stop prescribed diabetes medication because of a single low reading.

Repeated episodes should prompt review by your healthcare professional.

Monitor Your Glucose

Regular glucose monitoring can help identify patterns.

Depending on your treatment, useful times may include:

• before meals,
• before driving,
• before and after exercise,
• before bed,
• during illness,
• and whenever symptoms occur.

Your healthcare team can advise how frequently you should check.

Consider Continuous Glucose Monitoring

A continuous glucose monitor (CGM) uses a small sensor to track glucose throughout the day and night.

Many systems can alert users when glucose:

• is falling,
• reaches a low level,
• or is predicted to become low.

Current diabetes guidelines increasingly support CGM for people who can benefit from it.

It can be particularly valuable for people experiencing frequent lows or impaired awareness.

Plan for Physical Activity

Exercise should not simply be avoided because it can lower glucose.

Instead:

• learn your glucose response,
• carry fast-acting carbohydrate,
• check glucose when appropriate,
• consider the timing of insulin,
• and follow your individualized diabetes plan.

Some activities can affect glucose for many hours afterward.

Carry Fast-Acting Carbohydrate

If you are at risk of hypoglycemia, keep an appropriate treatment readily available.

Examples include:

• glucose tablets,
• glucose gel,
• juice,
• or another reliable source of fast-acting carbohydrate.

Keep supplies:

• at home,
• at work,
• when exercising,
• and when travelling.

Check expiration dates periodically.

Have a Glucagon Plan

People at significant risk of severe hypoglycemia should discuss glucagon with their healthcare professional.

If glucagon is prescribed, people close to you should know:

• where it is,
• how to recognize severe hypoglycemia,
• and how to use it.

Having glucagon available is useful only if someone knows what to do with it during an emergency.

Hypoglycemia and Driving

Low blood glucose can seriously impair:

• concentration,
• judgment,
• vision,
• reaction time,
• and coordination.

This can make driving dangerous.

People at risk of hypoglycemia should follow the medical and legal driving requirements applicable where they live.

If symptoms develop while driving, stop driving as soon as it is safe to do so and treat the low according to your diabetes plan.

Do not resume driving until your glucose and mental functioning have safely recovered and applicable local guidance is satisfied.

When Should You Contact Your Healthcare Professional?

Arrange a medical review if:

• you frequently experience low blood glucose,
• episodes occur during sleep,
• you no longer recognize warning symptoms,
• your glucose repeatedly falls below 54 mg/dL (3.0 mmol/L),
• you have required another person's help,
• your medication appears to be causing lows,
• or you experience unexplained hypoglycemia without diabetes.

Repeated lows should not simply be accepted as an unavoidable part of diabetes.

Your treatment may need adjustment.

When Is Hypoglycemia an Emergency?

Seek emergency medical assistance when a person with suspected hypoglycemia:

• becomes unconscious,
• has a seizure,
• cannot swallow safely,
• is severely confused,
• cannot treat themselves,
• does not respond appropriately to treatment,
• or has persistent or recurring severe symptoms.

Do not force food or drink into the mouth of someone who cannot swallow safely.

Use glucagon if it has been prescribed, is available and someone knows how to administer it.

The Bottom Line

Hypoglycemia means that blood glucose has fallen too low.

For many people with diabetes, a reading below 70 mg/dL (3.9 mmol/L) is considered low and requires action.

Common warning symptoms include:

• shaking,
• sweating,
• hunger,
• dizziness,
• rapid heartbeat,
• irritability,
• and confusion.

An alert person who can safely swallow can often treat a low using approximately 15 grams of fast-acting carbohydrate, waiting 15 minutes and checking glucose again.

Severe hypoglycemia is different.

If a person:

• becomes unconscious,
• has a seizure,
• cannot swallow,
• or needs another person's assistance,

do not give food or drink by mouth.

Use prescribed glucagon when appropriate and seek emergency medical assistance.

People who experience repeated hypoglycemia should have their diabetes treatment reviewed.

With appropriate medication management, glucose monitoring, meal planning, exercise planning and emergency preparation, many episodes can be prevented or treated before they become severe.

Medical Disclaimer

This article provides general health information for an international audience and is not a substitute for individualized medical care. Glucose targets and hypoglycemia treatment plans may differ according to age, diabetes treatment, pregnancy, medical conditions and other circumstances. Children may require different carbohydrate amounts for treating low glucose. Do not change insulin or other diabetes medicines without appropriate professional guidance. Severe hypoglycemia, seizures or loss of consciousness require urgent medical attention.

Sources and Further Reading

National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) — Low Blood Glucose (Hypoglycemia)

https://www.niddk.nih.gov/health-information/diabetes/overview/preventing-problems/low-blood-glucose-hypoglycemia

Centers for Disease Control and Prevention — Low Blood Sugar (Hypoglycemia)

https://www.cdc.gov/diabetes/about/low-blood-sugar-hypoglycemia.html

Centers for Disease Control and Prevention — Treatment of Low Blood Sugar (Hypoglycemia)

https://www.cdc.gov/diabetes/treatment/treatment-low-blood-sugar-hypoglycemia.html

American Diabetes Association — Standards of Care in Diabetes

https://professional.diabetes.org/standards-of-care