Hypoglycaemia (low blood sugar)


Hypoglycaemia (low blood sugar)


Hypoglycaemia, or a "hypo", is an abnormally low level of sugar (glucose) in your blood.

When your glucose level is too low, your body doesn't have enough energy to carry out its activities.

Hypoglycaemia is most commonly associated with diabetes and mainly occurs if someone with diabetes takes too much insulin, misses a meal or exercises too hard.

People who do not have diabetes can also experience hypoglycaemia, although this is much rarer. It can be triggered by malnutrition, binge drinking or certain conditions, such as Addison's disease..

What are the symptoms of hypoglycaemia?

Most people will have some warning that their blood glucose levels are too low, which gives them time to correct them. Symptoms usually occur when blood sugar levels drop to between 3 and 4 millimoles per litre (mmol).

Typical early warning signs are feeling hungry, trembling or shakiness, and sweating. In more severe cases, there can also be confusion and difficulty concentrating. In some severe cases, the person experiencing hypoglycaemia will lose consciousness.

It's also possible for hypoglycaemia to occur during sleep, which can cause excess sweating, disturbed sleep, and feeling tired and confused upon waking.

Correcting hypoglycaemia

The immediate treatment for hypoglycaemia is to have some food or drink that contains sugar, such as dextrose tablets or fruit juice, to correct your blood glucose levels.

After having something sugary, you may need to have a longer-acting "starchy" carbohydrate food, such as a few biscuits or a sandwich.

If hypoglycaemia causes someone to lose consciousness, an injection of the hormone glucagon can be given to raise blood glucose levels and restore consciousness. This is only if an injection is available and you know how to use it.

If a glucagon injection kit it not available, there is nobody trained to give the injection or the injection is ineffective after 10 minutes, call 999 for an ambulance.

Never try to put food or drink into the mouth of someone who is drowsy or unconscious, as they could choke. This includes some of the high sugar preparations specifically designed for smearing inside the cheek.

Preventing hypoglycaemia

If you have diabetes that requires treatment with insulin, the safest way of avoiding hypoglycaemia is to regularly check your blood sugar and learn to recognise the early symptoms.

Missing meals or snacks or eating less carbohydrate than planned can increase your risk of hypoglycaemia. Be careful when drinking alcohol as this can also cause hypoglycaemia, sometimes many hours after drinking.

Exercise or activity is also an important cause of hypoglycaemia and you should have a plan for dealing with this, such as eating carbohydrate before, during or after exercise, or adjusting your insulin dose.

You should also make sure you regularly change where you inject your insulin, as the amount of insulin your body absorbs can be different depending on where it is injected.

Always carry rapid acting carbohydrate with you, such as glucose tablets, a carton of fruit juice (one that contains sugar) or some sweets in case you feel symptoms coming on or your blood glucose level is low.

Make sure your friends and family know about your diabetes and the risk of hypoglycaemia. It may also help to carry some form of identification that lets people know about your condition in an emergency.

When hypoglycaemia occurs because of an underlying condition other than diabetes, the condition will also need to be treated to prevent a further hypo.

Symptoms of hypoglycaemia 

The symptoms of hypoglycaemia usually begin when a person's blood glucose level drops to somewhere between 3 and 4 millimoles (mmol) per litre.

If you have diabetes, particularly if it's treated with insulin, you may be advised to use a small device called a blood glucose meter to check your blood glucose levels regularly.

The symptoms may vary from person to person and it is important to be aware of the early warning signs so that you can treat them.

Symptoms and signs of hypoglycaemia can include:

feeling hungry



tiredness (fatigue)

blurred vision

trembling or shakiness

going pale

fast pulse or palpitations

tingling lips


difficulty concentrating


disorderly or irrational behaviour, which may be mistaken for drunkenness

If hypoglycaemia isn't treated promptly and blood glucose levels drop low enough, you may become drowsy or even lose consciousness.

Most people with insulin-treated diabetes notice that symptoms of hypoglycaemia change and become less obvious the longer they live with the condition.

Some people experience greatly reduced warning symptoms, putting them at significant risk of having severe episodes where they are dependent on others for help. It is important that people who develop this problem let their diabetes team know as their treatment may need to be changed to try to reduce this risk.

Hypoglycaemia while sleeping

Having a hypo while you're asleep is known as nocturnal hypoglycaemia. It is more common in people who treat diabetes with insulin.

Although some people find their sleep is disturbed when they experience nocturnal hypoglycaemia, you will often only notice the symptoms when you wake up in the morning. The symptoms can include:

headache, which is often likened to having a hangover

feeling unusually tired in the morning

damp sheets or clothing from sweating

Causes of hypoglycaemia 

In most cases hypoglycaemia occurs in people with diabetes, although in rarer cases it can occur because of other underlying conditions.

Hypoglycaemia in people with diabetes

Overdose of diabetes medication

A common cause of hypoglycaemia is taking too much insulin for your current needs. Insulin is a medication that helps control your blood glucose levels. It is commonly used to treat type 1 diabetes, but it's also recommended for some people with type 2 diabetes.

A drop in blood glucose levels can also happen when you take too much oral hypoglycaemia medication such as sulphonylurea, which causes a release of insulin. This medication is often used to lower blood glucose levels in people with type 2 diabetes.

Exercise, food and alcohol

For people with type 1 diabetes, maintaining the correct blood glucose level involves balancing the amount of insulin you inject, the amount of food you eat and the amount of energy you burn during exercise.

Hypoglycaemia may occur if you have taken your dose of insulin as usual but your carbohydrate intake is lower than normal or has been used up more quickly. This may happen if you delay or miss a meal or snack, do not eat enough carbohydrate or do more exercise than usual.

Hypoglycaemia may also occur in people with diabetes who have drunk too much alcohol or who have drunk alcohol on an empty stomach.

However, it is not always possible to identify why a particular episode of hypoglycaemia has occurred as sometimes it happens in people with diabetes for no obvious reason.

Hypoglycaemia in people without diabetes

Hypoglycaemia (even mild cases) is very rare in people who don't have diabetes. The possible causes of hypoglycaemia in people without diabetes are outlined below.

Reactive hypoglycaemia

People without diabetes can sometimes experience hypoglycaemia if their pancreas produces too much insulin after a large carbohydrate-based meal. This is known as reactive hypoglycaemia. It is not clear why this happens, although it is thought to be more common in people who are overweight or have had gastric bypass surgery.

In rare cases, a benign (non-cancerous) tumour in the pancreas may cause an overproduction of insulin, or the tumour itself may use up too much glucose.

Other causes

Other possible causes of hypoglycaemia in people without diabetes are:

fasting or malnutrition – where you are not consuming enough nutrients for your body to function properly

binge drinking or heavy drinking of alcohol

Addison's disease – a disorder of the adrenal glands

certain medication – hypoglycaemia has been known to occur in people taking quinine (for malaria), salicylates (for rheumatic disease) and propranolol (for high blood pressure)

severe illnesses affecting the liver, kidneys or thyroid gland

Treating hypoglycaemia 

In most cases, hypoglycaemia can be self-treated when you recognise the symptoms.

Treating an episode of hypoglycaemia

The immediate treatment for hypoglycaemia is to have some sugary food or drink (about 15g of rapidly acting carbohydrate) to end the attack.

For example, try:

a glass of fruit juice or non-diet soft drink

between three and five dextrose tablets

a handful of sweets

At first you should avoid fatty foods and drinks such as chocolate and milk, because they don't usually contain as much sugar and may cause the sugar to be absorbed more slowly.

After having something sugary, you should have a longer-acting carbohydrate food, such as a few biscuits, a cereal bar, a piece of fruit or a sandwich.

It will usually take 10-15 minutes to recover from mild episodes of hypoglycaemia. If you have a blood glucose meter, you should measure your blood sugar again and if it is still too low (below 4 mmol) you should have some more sugary food or a drink and test your levels again in another 10-15 minutes.

If normal treatment is not effective, you may be able to help the person by applying glucose gel (or honey, treacle or jam if this is not available) to the inside of their cheeks and gently massaging the outside of their cheeks. It may take 10-15 minutes before they feel better. This should not be done if the person is drowsy or unconscious because of the risk of choking.

If you have several episodes of hypoglycaemia a week, you should contact your diabetes care provider to find out the underlying cause. You may need your medication adjusted or there may be another condition causing hypoglycaemia that needs to be treated.

If a person is unconscious

If a person loses consciousness because of severe hypoglycaemia, they need to be put into the recovery position and should be given an injection of the hormone glucagon if they have an injection kit. This injection raises the blood glucose level.

The injection is best done by a friend or family member who knows what they are doing, or by a trained healthcare professional.

If a glucagon injection kit it not available or there is nobody available who is trained to give the injection, or if the injection is ineffective after 10 minutes, call 999 for an ambulance. Never try to put food or drink into the mouth of someone who is unconscious, as they could choke.

If you are able to give a glucagon injection and the person regains consciousness, they should eat some longer-acting carbohydrate food, such as a few biscuits, a cereal bar or a sandwich. You should continue to monitor the person for signs of recurring symptoms in case they need to be treated again.

See hypoglycaemia medicines information for more about the medicines used to treat the condition.


Preventing hypoglycaemia 

If you have diabetes, sticking to your medication plan and eating regular meals can help prevent hypoglycaemia.

It is also important to monitor your blood sugar (glucose) levels.

Monitoring your blood glucose

Regularly checking your blood sugar levels can help you spot hypoglycaemia quickly. You can monitor your own blood glucose levels using a simple finger prick blood test.

See treating type 1 diabetes and treating type 2 diabetes for more information about blood glucose tests.

Eat regularly and limit alcohol

If you have diabetes, strenuous physical activity can lead to hypoglycaemia. Eating extra carbohydrate-based foods before and during exercise can help reduce the chances of this happening. If you are taking insulin, your doctor may advise you about lowering your dose before you do strenuous physical activity.

Alcohol can also affect your body's ability to release glucose. If you have type 1 diabetes, you are advised to drink no more than 2-3 units of alcohol a day and to eat a snack after drinking alcohol.

Spot the signs early and make others aware

As hypoglycaemia can develop suddenly, it is important to be aware of the symptoms of hypoglycaemia so you can treat it quickly. Tell your friends and family about signs to look for and let them know how to treat it.

People with diabetes are advised to carry a form of identification with them that states their condition so that they can be helped quickly and efficiently.

Make sure treatment is readily available

If you are at risk of hypoglycaemia, you should carry sugary food and drink with you at all times to treat mild cases as soon as possible.

If you have diabetes, particularly type 1 diabetes, your doctor may recommend medications such as glucose gel to carry with you. Glucose gel can be used to treat hypoglycaemia that doesn't respond to normal treatment.

If you are being treated with insulin, you will usually be given a kit containing an injection of a medication called glucagon. Members of your family or your carer can be trained to carry out the injection, which should be used if you lose consciousness because of severe hypoglycaemia.

Preventing hypoglycaemia at night

It's important to avoid recurrent hypoglycaemia during the night (nocturnal hypoglycaemia) as this can reduce the early symptoms of daytime episodes. If you experience nocturnal hypoglycaemia, you can try:

keeping something sugary by your bedside

having a snack before bedtime, such as biscuits and milk

checking your blood glucose levels between 3am and 4am, when hypoglycaemia is most likely to occur

Hypoglycaemia and driving

As hypoglycaemia can cause confusion, drowsiness, or even unconsciousness, this can present a significant risk to you or other road users. If you have diabetes requiring treatment with insulin, you must:

inform the DVLA and your insurance company

test your blood sugar before driving and at regular intervals (at least every two hours) while driving

avoid driving if your blood glucose is low

avoid driving for 45 minutes after treating hypoglycaemia

carry rapid acting carbohydrates with you in the vehicle at all times

If you experience hypoglycaemia while driving, you should pull over and stop as soon as it is safe to do so. You should remove the keys from the ignition and get out of the driver's seat before treating the condition in the normal way.

If you have two or more episodes of hypoglycaemia that require assistance in a 12 month period, it is a legal requirement to stop driving and inform the DVLA. If you are a group 2 driver (licence to drive buses, coaches or lorries), it is a legal requirement to stop driving group 2 vehicles immediately and inform the DVLA if you have a single episode of hypoglycaemia requiring assistance.

You should inform your diabetes team if you start to have problems recognising hypoglycaemia or start to have more regular episodes,even if there were warning symptoms and you were able to treat these without assistance.