Low blood sugar (hypoglycaemia or hypos)

Diabetes treatment and the safe use of insulin

Hypoglycaemia or a hypo is a low blood sugar level. This is the main side effect of insulin treatment. You have a hypo if your blood sugar level drops below 4mmol/L.

A growing group of people with diabetes use a continuous glucose monitor or flash monitor. The monitor allows you to check your sugar level at any time.

If the monitor shows a reading below 4mmol/L, it is best to confirm this by doing a finger prick blood test. This helps you to get the most accurate result.

You also need to do a finger prick blood test if your reading does not match how you feel. For example, this could be when you have the symptoms of a hypo but your monitor shows a reading above 4mmol/L.

If there are errors with your insulin treatment, your blood sugar level could drop too low. A hypo can be dangerous if you do not treat it quickly. You need to know the symptoms of low blood sugar, and how to treat and avoid hypos.

Symptoms of hypos

Each person has different symptoms, but the most common early signs of hypos include:

  • sweating heavily
  • feeling tired suddenly or having trouble concentrating
  • dizziness
  • feeling anxious or irritable
  • trembling or shaking
  • tingling lips
  • feeling hungry
  • going pale
  • a fast, pounding or racing heartbeat (palpitations)

If you do not treat a hypo, you might get more severe symptoms.

How to treat hypos

Follow these steps immediately to treat a hypo yourself:

  1. Have a sugary drink or snack. A suitable drink is a small 150 to 200ml glass of non-diet fizzy drink or fruit juice. A suitable snack is 15 to 20g of a fast-acting carbohydrate. Examples are 3 to 4 jelly babies, 4 to 6 glucose tablets or 1 tube of glucose gel.
  2. Test your blood sugar level after 10 to 15 minutes. If it has improved and you feel better, move to step 3. But if there is little or no change, have another sugary drink or snack. Measure your blood sugar level again after 10 to 15 minutes.
  3. You need to prevent your blood sugar level from dropping again. Eat your next meal if it is due and contains a starchy carbohydrate, such as bread, pasta, potato or rice. Otherwise, have a snack that contains a slow-release carbohydrate. Examples are a slice of bread or toast, 2 digestive biscuits or a glass of cows’ milk.

How to treat a severe hypo

It is important that your family and friends know what to do if you have a severe hypo and cannot treat this yourself. They must not give you any food or drink if you are unconscious.

They need to give you a glucagon injection (which releases stored sugar from your liver) or call 999 and ask for an ambulance. The NHS website explains what to do in more detail.

How to avoid hypos

There are things that you can do to avoid hypos.


  • check your blood sugar level regularly
  • test your blood sugar level before driving
  • check how your blood sugar level is changing if you have a continuous glucose monitor or flash monitor. You may be able to set an alarm to warn you if your blood sugar level goes too low
  • take your insulin at recommended doses and times
  • always carry a sugary snack or drink and equipment to test your sugar level
  • reduce your insulin doses before and after exercise, if needed


  • do not miss meals
  • do not drive if your blood sugar level is less than 5mmol/L
  • do not drink more than the recommended alcohol limits (14 units of alcohol a week for men or women)
  • do not drink on an empty stomach

If you have a lot of hypos or any severe hypos, please ask to see the specialist diabetes team.

Resource number: 3477/VER3
Last reviewed: October 2022
Next review due: October 2025

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