Low blood sugar: what to do

How to spot and treat low blood sugar (hypoglycemia) with the rule of 15, when to use glucagon and call 9-1-1, and how to stay safe while driving.

6 min read · last reviewed October 3, 2026

If you take insulin or certain diabetes pills, your blood sugar can sometimes drop too low. This is called low blood sugar, or hypoglycemia (a "low" or a "hypo" for short). Lows are common, and most are mild and easy to treat. Knowing what to do, and teaching the people around you, keeps you safe and helps you feel more confident.

Who can get low blood sugar?

Lows mostly happen to people who take:

• insulin, or
• pills that make the body release more insulin, such as sulfonylureas (for example, gliclazide or glyburide).

Many other diabetes medicines, such as metformin, rarely cause lows on their own. Ask your team or pharmacist, "Can any of my medicines cause low blood sugar?"

Common triggers include a delayed or smaller meal, more activity than usual, too much insulin, or drinking alcohol (which can cause lows up to a day later).

What counts as low?

For most people with diabetes, a reading below 4.0 mmol/L (about 70 mg/dL) is low. Some newer materials use 3.9 mmol/L. Your team will tell you what number to act on.

Know the signs

Everyone's signs are a little different. Common ones include:

• shaking, sweating, or a pounding heart
• feeling hungry, anxious or cranky
• tingling lips
• headache, dizziness or blurry vision
• trouble concentrating, confusion or acting "not like yourself"
• weakness or feeling very sleepy

Lows can also happen during sleep. Nightmares, sweaty sheets or a morning headache can be clues. Some people, especially after many years of diabetes, stop feeling the early signs. If that's you, tell your team. A continuous glucose monitor (CGM) with alarms can help.

Something you can do today: Write down your own low signs and share them with your family.

Treat it fast: the rule of 15

If you feel low, check your blood sugar if you can. If you can't check, treat anyway.

1. Eat or drink 15 grams of fast-acting sugar. Diabetes Canada suggests choices like:

• glucose tablets (check the label for how many make 15 grams)
• 2/3 cup (150 mL) of juice or regular (not diet) pop
• 1 tablespoon (15 mL) of sugar dissolved in water, or 3 sugar packets
• 1 tablespoon (15 mL) of honey
• hard candies (check the label: about 6 small mints or candies make 15 grams)

1. Wait 15 minutes, then check again.
2. If you're still below 4.0 mmol/L, treat again with another 15 grams.
3. Once you're back in range, have your next meal if it's due. If it's more than an hour away, have a snack with carbohydrate and protein, such as crackers and cheese.

Skip chocolate, cookies or nuts to treat a low. The fat slows down how fast the sugar gets into your blood.

Something you can do today: Put glucose tablets or a small juice box in your bag, your car and by your bed.

Severe lows: when someone needs help

A severe low is when you need help from another person. You might be very confused, unable to swallow safely, passed out or having a seizure.

If the person is awake and can swallow safely: help them take fast-acting sugar. Diabetes Canada suggests 20 grams for a severe low in a person who is awake. Stay with them and re-check in 15 minutes.

If the person is passed out, having a seizure, or can't swallow:

• Call 9-1-1 or your local emergency number.
• Never put food or drink in their mouth. They could choke.
• Give glucagon if it's available and you've been shown how.
• Turn them on their side, and stay with them until help arrives.

About glucagon

Glucagon is a hormone that quickly raises blood sugar. It comes as a nasal spray or a ready-to-use injection. If you take insulin, ask your team whether you should have glucagon at home. Show your family, friends and coworkers where it is and how to use it. Check the expiry date. After a severe low, always tell your team. Your treatment may need to change.

Something you can do this week: Practise with your family, using a glucagon trainer or video from your pharmacist.

Driving safely

A low while driving can be dangerous, but a few habits make a big difference. Diabetes Canada's advice for drivers who take insulin or pills that can cause lows:

• Check before you drive, and about every 4 hours on long drives.
• "Above 5 to drive." If your blood sugar is below 5.0 mmol/L (about 90 mg/dL), eat a snack with carbohydrate and re-check before you start. Commercial drivers may have stricter rules.
• Don't drive if you're low. Treat it, wait until you're above 5.0 mmol/L, and know that your brain can take up to 40 minutes to fully recover after a low.
• If you feel low while driving, pull over safely, turn off the engine, take the keys out of the ignition and treat the low.
• Keep fast-acting sugar and your meter or CGM within reach in the car.

See Driving, work and travel with diabetes for licensing rules.

Preventing lows

• Don't skip meals if you take insulin or a sulfonylurea.
• Check more often when you're more active, drinking alcohol, sick or travelling.
• Eat something with alcohol, and never drink on an empty stomach.
• Wear medical ID that says you have diabetes.
• If you have lows often, talk with your team. A change in medicine or timing often helps.

Questions to ask your care team

• Can any of my medicines cause low blood sugar?
• What number should I treat as low?
• Should I have glucagon? Who should learn to use it?
• Would a CGM with alarms help me?
• What should I do with my medicines before exercise or when I drink alcohol?
• What are the driving rules where I live?

This article is general information, not medical advice. Talk with your health care team about your own situation. In an emergency, call 9-1-1 or your local emergency number.

In an emergency, call 9-1-1 or your local emergency number.

General information, not medical advice. It does not replace your own care team. If you think you or someone else is having a medical emergency, call 9-1-1 or your local emergency number. If you are in crisis or thinking about suicide, call or text 9-8-8 (Canada and the US).

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