Hypoglycemia: What Published Guidance Supports

Key takeaways

• Commonly defined as: below 70 mg/dL
• Early symptoms: shakiness, sweating, hunger, anxiety, fast heartbeat
• Most useful single change: Carry fast-acting carbohydrate, such as glucose tablets or juice, at all times.
• Commonest mistake: Driving when your glucose is low or you feel any symptoms.
• See a doctor if any of the signs under "When to speak to a doctor" below apply to you.

What it is

Blood glucose falling too low, usually in people taking insulin or sulfonylureas. It sits within Diabetes. The figures come from the bodies named at the foot of this page.

The numbers, in one place

What helps

The advice below comes straight from the guidance cited at the foot of this page.

• Carry fast-acting carbohydrate, such as glucose tablets or juice, at all times
• Check your glucose before driving and regularly on long drives
• Follow up with a snack or meal once your glucose is back in range
• Ask about a glucagon prescription and show the people around you how to use it

What to avoid

The common mistakes, including the ones that sound sensible.

• Driving when your glucose is low or you feel any symptoms
• Treating with chocolate or cookies, whose fat slows the rise
• Ignoring repeated episodes rather than reviewing treatment

In depth

Your brain relies almost entirely on glucose for fuel and cannot store much of it. When glucose falls, the body first responds with stress hormones such as epinephrine (adrenaline), which cause the shaking, sweating, hunger and pounding heart that warn you something is wrong. If glucose keeps falling, the brain itself is short of fuel, causing confusion, odd behavior, slurred speech, blurred vision and eventually seizures or loss of consciousness.

Most serious lows happen in people taking insulin or sulfonylureas, medicines that keep lowering glucose regardless of how much you have eaten. A dose that is right on an ordinary day can be too much if you skip a meal, exercise more than usual, drink alcohol or lose weight. Other common diabetes medicines, such as metformin, SGLT2 inhibitors and GLP-1 receptor agonists, rarely cause lows on their own but can add to the effect of insulin or sulfonylureas.

Lows are commonly grouped by severity. Below 70 mg/dL is a level to act on, below 54 mg/dL is clinically significant and needs prompt treatment, and a severe low is any episode where you need help from someone else to recover. Repeated lows can blunt the warning symptoms, a condition called hypoglycemia unawareness, which makes future lows more dangerous. Fortunately, avoiding lows for a few weeks often helps the warning signs return.

Signs and symptoms

• Shakiness, sweating, chills or clamminess
• Hunger, nausea, or tingling around the lips
• Fast heartbeat, anxiety or irritability
• Dizziness, weakness or sudden tiredness
• Confusion, difficulty concentrating, or behaving as if drunk
• Blurred or double vision and slurred speech
• Nightmares, waking damp with sweat or a morning headache after an overnight low

Causes and risk factors

• Taking more insulin or sulfonylurea than needed, or taking it at the wrong time
• Delayed, missed or smaller meals than usual
• More physical activity than usual, with effects lasting into the night
• Drinking alcohol, especially without food, which blocks the liver from releasing glucose
• Weight loss or improved fitness that lowers insulin needs
• Declining kidney function, which slows clearance of some medicines
• Previous recent lows, which blunt the body's defenses

How it is checked

In people with diabetes, a low is confirmed by a finger-stick or sensor reading below 70 mg/dL, ideally taken when symptoms occur. If you cannot check, treat anyway; it is safer to treat a possible low than to wait. Your care team will review meter or sensor data for patterns, such as lows after exercise, in the late afternoon or overnight, and ask whether you still feel early warning symptoms.

In people without diabetes, true hypoglycemia is uncommon and needs a different approach. Doctors look for three things together: symptoms, a measured low glucose and relief when glucose is raised. If these are confirmed, investigations may look for medicines, hormone problems, liver or kidney disease or, rarely, an insulin-producing tumor.

Treatment and support options

Treating a low

Use the 15-15 rule: take 15 g of fast-acting carbohydrate, such as glucose tablets, half a cup (4 ounces) of juice or regular soda, or a tablespoon of sugar or honey, then recheck after 15 minutes. Repeat if you are still below 70 mg/dL. Once you are back in range, eat a snack or meal if your next meal is more than an hour away, to stop glucose falling again.

Glucagon for emergencies

Glucagon is a hormone that makes the liver release stored glucose. It now comes as a nasal powder and as ready-to-use injections that are much simpler than older kits. Anyone who takes insulin, or who has had a severe low, should ask for a prescription and make sure family, friends and coworkers know where it is and how to use it.

Adjusting treatment

Repeated lows are a sign that your treatment needs to change, not that you should simply eat more. Your doctor may reduce or retime insulin, switch away from a sulfonylurea, or recommend medicines with lower low-blood-sugar risk. Continuous glucose monitors with alerts can warn you before a low becomes serious, and some insulin pumps automatically reduce insulin when glucose is falling.

Prevention

• Check glucose before driving, exercise and bedtime if you take insulin or sulfonylureas
• Carry fast-acting carbohydrate everywhere, including in the car and at the gym
• Eat something when drinking alcohol and check glucose before sleep
• Plan extra carbohydrate or reduced insulin for longer or more intense exercise
• Wear medical identification stating that you have diabetes
• Ask about a continuous glucose monitor with low alerts if you have frequent or unnoticed lows

Day to day

Living with the risk of lows is partly practical and partly emotional. Keep supplies in every bag, jacket and car, and replace them after use. Learn your own early signs, which can change over time, and teach the people around you what a low looks like, since confusion can stop you recognizing it yourself. Coworkers, teachers and coaches benefit from a simple written plan.

Fear of lows is common, and it can lead people to keep glucose deliberately high or avoid exercise. Talk to your care team if this is happening; there are ways to adjust medicines, use technology and plan for activity that reduce risk while keeping you active. Following a severe low, it is worth reviewing what happened, without blame, to see what can be changed.

For specific groups

Older adults

Older adults may have fewer warning symptoms, and lows can look like confusion, dizziness or a fall. Kidney changes slow medicine clearance, raising the risk. Doctors often relax glucose targets and favor medicines that rarely cause lows in this age group.

Children and teens

Children may not recognize or explain a low and can seem cranky, pale or unusually quiet. Schools need a care plan, supplies and trained staff who can give glucagon. Teens face added risks from alcohol, irregular meals, sports and driving.

Pregnancy

Glucose targets are stricter in pregnancy, and insulin needs change quickly, especially in the first trimester, so lows become more frequent. Close monitoring, a glucagon prescription and a clear plan from your care team are important. Lows can also be harder to notice in pregnancy, so checking often, especially before driving, matters even more.

Questions to ask your doctor

• Do any of my medicines put me at risk of low blood sugar?
• What should I do differently on days when I exercise?
• Should I have a glucagon prescription, and who should learn to use it?
• Would a continuous glucose monitor with alerts help me?
• I am having lows overnight; how should my treatment change?
• How long should I wait after a low before driving?

More questions, answered

Why not treat a low with chocolate?

Chocolate and other high-fat foods slow digestion, so the sugar reaches your blood more slowly. When you are low, you want glucose to rise quickly. Glucose tablets, juice or regular soda work faster. Save fat- and protein-containing snacks for after your glucose is back in range.

Can I have a low while asleep?

Yes. Overnight lows are common in people on insulin, especially after exercise or alcohol. Signs include nightmares, waking sweaty, a morning headache or feeling hungover. Checking glucose at bedtime, a sensor with alarms and treatment adjustments can reduce the risk.

Is it safe to exercise if I take insulin?

Yes, and exercise is valuable. Check glucose before, during longer sessions, and after. You may need extra carbohydrate or a lower insulin dose, and lows can occur hours later. Your care team can help you build a plan for the types of activity you do.

Can people without diabetes have low blood sugar?

It is uncommon, but it can happen, for example after some types of stomach surgery, with certain medicines, heavy drinking, or rare hormone or tumor conditions. Feeling shaky when hungry is usually not true hypoglycemia. If you have repeated symptoms, see your doctor for proper testing.

What if I cannot check my glucose?

If you have symptoms of a low and cannot check, treat it anyway with fast-acting carbohydrate. Treating a possible low is much safer than waiting. Check as soon as you can afterward and mention the episode to your care team.

Does alcohol cause lows?

It can, especially in people on insulin or sulfonylureas. Alcohol interferes with the liver releasing glucose, and the effect can last many hours. Eat when you drink, check glucose before bed and be aware that the symptoms of a low can be mistaken for drunkenness.

Related topics

• What the Guidance Really Says About Medicines and Driving (Medicines Safety)
• Gestational Diabetes: Sorting the Evidence From the Noise (Pregnancy and Postpartum)
• Acute Kidney Injury: What the Evidence Actually Says (Kidney Health)
• What the Guidance Really Says About Sick Day Rules (Long-Term Conditions)

Where to go next

• Starting Out With Hypoglycemia
• Hypoglycemia: Common Questions Answered
• Hypoglycemia — the reference entry
• Diabetes: The Complete Guide
• Diabetic Eye Screening: Sorting the Evidence From the Noise
• Carbohydrates and Blood Glucose: Sorting the Evidence From the Noise

When to speak to a doctor

Call 911 if someone with diabetes becomes unconscious, has a seizure, or cannot swallow safely — give glucagon if it is available, but do not put food or drink in their mouth. See your doctor about repeated episodes, loss of the early warning symptoms, or episodes overnight.

Where this comes from

• National Institute of Diabetes and Digestive and Kidney Diseases — Low Blood Glucose (Hypoglycemia)
• American Diabetes Association — Standards of Care in Diabetes

How this page was put together

Every figure, recommendation and warning above is taken from the guidance named in Where this comes from. Nothing on this page is inferred, summarized or generalized beyond what those bodies publish: where they give a number, it is their number, and where they are silent, so are we. Pages are rebuilt whenever the underlying record changes. Sign-off by a named clinician, where it has happened, is shown at the top of the page along with the date.

Medical disclaimer

This article is general information, not medical advice. It cannot account for your own history, medication or circumstances. Always speak to your doctor, pharmacist or another qualified health professional before making changes that affect your treatment, and never delay seeking medical advice because of something you have read here. In an emergency, call 911.