Hypoglycemia (Low Blood Sugar): Signs, Treatment, and Prevention

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Last reviewed: October 9, 2026 · Sources: CDC, NIH/NIDDK, American Diabetes Association

Hypoglycemia, or low blood sugar, happens when the level of glucose in your blood drops below what your body needs. It is most common in people who take insulin or certain diabetes pills, and it can come on quickly. Knowing the signs and how to treat a low can prevent a mild episode from becoming an emergency. This guide explains causes, symptoms, treatment with the 15-15 rule, severe hypoglycemia and glucagon, and prevention.

What counts as low blood sugar?

Blood glucose below 70 mg/dL is generally considered low. The American Diabetes Association describes levels of hypoglycemia:

Level 1: Glucose below 70 mg/dL but at or above 54 mg/dL.
Level 2: Glucose below 54 mg/dL, which is considered clinically significant and needs immediate action.
Level 3 (severe): A low with confusion or other changes in mental or physical functioning that requires help from another person to treat, regardless of the number.

Your care team may give you a different target or threshold based on your situation.

Who is at risk?

According to NIDDK, low blood glucose is most common among people who take insulin, but it can also occur with some diabetes pills, especially sulfonylureas and meglitinides, which increase insulin release. People who manage diabetes with eating and activity alone, or who take medicines that do not cause the body to release more insulin, rarely have hypoglycemia from their diabetes treatment.

Common causes

Taking too much insulin or a mismatch between insulin timing and food
Skipping or delaying a meal, or eating fewer carbohydrates than planned
More physical activity than usual, which can lower glucose during and for hours after exercise
Drinking alcohol, especially without food
Weight loss or changes in kidney function that change how medicines work
Illness that reduces appetite or causes vomiting

Symptoms

Symptoms vary from person to person and can change over time. Common symptoms include:

Shakiness or trembling
Sweating, chills, or clamminess
Fast heartbeat
Hunger
Nervousness, anxiety, or irritability
Dizziness or lightheadedness
Blurred vision
Headache
Weakness or fatigue
Confusion, difficulty concentrating, or unusual behavior
Tingling or numbness in the lips or tongue

Severe lows can cause clumsiness, inability to eat or drink, seizures, or loss of consciousness.

Lows during sleep

Hypoglycemia can happen overnight. Signs may include nightmares, sweating through pajamas or sheets, or waking up tired, irritable, or with a headache. A continuous glucose monitor with alarms can help catch overnight lows.

Hypoglycemia unawareness

Some people, particularly those who have had diabetes for a long time or have frequent lows, stop feeling the early warning symptoms. This is called hypoglycemia unawareness and raises the risk of severe lows. Tell your care team if you notice lows without symptoms; strictly avoiding lows for a period can sometimes help restore awareness. CGMs with alerts are very helpful in this situation.

How to treat a low: the 15-15 rule

If you think your blood sugar is low, check it if you can. If you cannot check, treat it anyway. The ADA and NIDDK describe the 15-15 rule:

Eat or drink 15 grams of fast-acting carbohydrate.
Wait 15 minutes and recheck your blood glucose.
If it is still below 70 mg/dL, have another 15 grams of fast-acting carbohydrate.
Repeat until your blood glucose is at least 70 mg/dL.
Once in range, eat a meal or snack if your next meal is more than an hour or so away, to prevent another low.

Examples of 15 grams of fast-acting carbohydrate

Glucose tablets (check the label for the number needed)
A gel tube of glucose (check the label)
4 ounces (half a cup) of juice or regular (not diet) soda
1 tablespoon of sugar, honey, or syrup
Hard candies or jellybeans (check the label for how many)

Avoid treating lows with foods high in fat or protein, such as chocolate or peanut butter. Fat slows the absorption of sugar, and protein does not raise blood glucose quickly. Children usually need smaller amounts; ask your child's provider.

Avoid overtreating

It is tempting to keep eating until symptoms go away, but symptoms can last after glucose has recovered. Overtreating can lead to high blood sugar. Waiting the full 15 minutes before rechecking helps.

Severe hypoglycemia and glucagon

Severe hypoglycemia is an emergency. If someone is unconscious, having a seizure, or unable to swallow safely, do not give food or drink by mouth because they could choke.

Glucagon is a hormone that raises blood glucose by signaling the liver to release stored glucose. It is available as a nasal powder, a ready-to-use injection, or a kit that must be mixed. NIDDK recommends that people at risk of severe lows ask their provider about glucagon and teach family members, friends, and coworkers how to use it.

Give glucagon according to the product instructions.
Turn the person on their side in case they vomit.
Call 911 if glucagon is not available, if the person does not respond within about 15 minutes, or as instructed.
Once the person is awake and can swallow, give them a source of sugar and then a snack.

Driving and hypoglycemia

Low blood sugar can impair driving. If you take insulin or medicines that can cause lows, check your glucose before driving and every so often on long drives, keep fast-acting carbohydrate in the car, and do not drive if your glucose is low. If a low starts while driving, pull over safely and treat it, then wait until your glucose and thinking have recovered.

Preventing hypoglycemia

Know your medicines. Ask whether your diabetes medicines can cause lows.
Check regularly. Check more often when routines change, before driving, and around exercise.
Plan meals. Don't skip meals if you take insulin or medicines that can cause lows.
Plan for exercise. Ask about adjusting insulin or eating extra carbs. See exercise and diabetes.
Be careful with alcohol. Drink only with food, and check your glucose, including before bed.
Carry supplies. Keep fast-acting carbs and your meter or CGM receiver with you.
Wear medical ID so others know you have diabetes.
Review patterns with your care team. Frequent lows mean your treatment plan may need to change. Older adults and people with other health conditions often benefit from less strict targets to avoid lows.

When to call your provider

Contact your care team if you have frequent lows, lows without warning symptoms, lows overnight, or any severe low. Call 911 for anyone who is unconscious or not responding to treatment.

Related guides

Learn about the opposite problem in hyperglycemia and DKA, how insulin works in insulin basics, and how to track your numbers in checking blood sugar and CGMs.

Key takeaways

Blood glucose below 70 mg/dL is generally considered low; below 54 mg/dL needs immediate action.
Lows are most common with insulin and some pills such as sulfonylureas.
Treat with 15 grams of fast-acting carbohydrate, recheck in 15 minutes, and repeat as needed.
Severe lows require glucagon or emergency help; never give food by mouth to someone who cannot swallow.

Sources

Links to the sources cited above appear in the text. We rely on the Centers for Disease Control and Prevention (CDC), the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), and the American Diabetes Association (ADA).

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