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Hypos (low blood sugar)

A hypo is when your blood sugar drops too low. Knowing the signs and treating it quickly keeps a hypo from becoming serious.

What a hypo is

A hypo, short for hypoglycaemia, is a blood sugar reading below 4 mmol/L. The NHS and Diabetes UK both use a simple reminder for this: “4 is the floor”. Hypos mainly affect people who take insulin, or certain type 2 medicines such as sulfonylureas, so if your treatment cannot cause a hypo you will rarely need this page – but it is still worth knowing the signs.

How a hypo feels

Early symptoms come on quickly and are your body's way of asking for sugar. Diabetes UK describes them as including:

  • Shaky or trembly. Feeling unsteady, sometimes with tingling lips.
  • Sweating. Often alongside going pale.
  • Hungry. A sudden, strong hunger.
  • Tired or dizzy. Trouble concentrating can come with this.
  • A fast or pounding heartbeat. Feeling anxious or irritable too.

If a hypo is not treated it can get worse – confusion, slurred speech, unusual behaviour, and eventually passing out or a seizure. That is why it is best to treat a hypo as soon as you notice the early signs rather than waiting to see if it passes.

What causes a hypo

A hypo usually happens when there is too much glucose-lowering medicine for the amount of sugar in your blood. Common causes include:

  • Too much insulin or diabetes medicine. A dose that was larger than your body needed.
  • A missed or delayed meal. Or eating less carbohydrate than usual.
  • More activity than usual. Exercise uses up glucose, sometimes for hours afterwards.
  • Alcohol. It can cause a delayed hypo several hours later, or overnight while you sleep.

How to treat a hypo

The NHS recommends the 15-15 approach: a fast-acting sugar first, then a re-check, repeating until you are back above 4.

The 15-15 steps

  1. Have 15 to 20g of a fast-acting carbohydrate – for example 4 to 5 glucose tablets, a small glass (about 150 to 200ml) of a sugary, non-diet fizzy drink or fruit juice, or 4 to 5 jelly babies.
  2. Wait 10 to 15 minutes, then check your blood sugar again.
  3. If it is still below 4, repeat the fast-acting carbohydrate.
  4. Once you are back above 4 and feel better, if your next meal is not soon have a snack with longer-acting carbohydrate – a slice of toast, a sandwich, or a piece of fruit.

Do not reach for chocolate or biscuits first – the fat in them slows the sugar down, so it takes longer to lift your blood sugar when you need it fast.

When a hypo is an emergency

A severe hypo is one you cannot treat yourself. This is where the person is very confused, cannot swallow safely, is unconscious, or is having a seizure.

Severe hypo: call 999

If someone with diabetes is very confused, cannot swallow safely, passes out or has a seizure, someone else should call 999.

  • Do not put food or drink in the mouth of someone who is not fully awake.
  • Put them in the recovery position while you wait for help.
  • If you are trained and a glucagon injection kit is to hand, it can be given.

See what to do in a diabetes emergency for the full steps.

After recovering from a severe hypo, tell your diabetes team – they can look at what led to it and help you avoid another.

Hypos and driving

The rule for drivers is “5 to drive”. Do not drive if your blood sugar is below 4, or below 5 and you are about to set off. Wait until it is back up and you feel well before driving.

Keep a record

Logging each hypo – the time, what you were doing and how you treated it – helps you and your team spot a pattern, such as hypos after exercise or overnight after alcohol. You can record a hypo in the app in a few taps, and bring the pattern to your next appointment.

Checked against NHS and NICE guidance on . See all official sources.