Hypoglycemia

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 get help" below apply to you.

Why it matters

It can develop quickly, impairs judgment exactly when judgment is needed, and is dangerous while driving.

The numbers, in one place

Published figures for Hypoglycemia

Measure	Figure
Commonly defined as	below 70 mg/dL
Early symptoms	shakiness, sweating, hunger, anxiety, fast heartbeat
Immediate treatment	15 g of fast-acting carbohydrate (the 15-15 rule)
Recheck after	15 minutes, and repeat if still below 70 mg/dL
Severe low	glucagon, given by someone else, if the person cannot swallow safely

What helps

• 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

• 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.

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

• Hypoglycemia: What Published Guidance Supports
• Making Sense of Hypoglycemia
• 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 get help

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.