Hypoglycaemia, or a "hypo", is an abnormally low level of glucose in your blood (less than four millimoles per litre).

When your glucose (sugar) 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.

In rare cases, it's possible for a person who doesn't have diabetes to experience hypoglycaemia. It can be triggered by malnutrition, binge drinking or certain conditions, such as Addison's disease.

Read more about the causes of hypoglycaemia

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 fall below four millimoles (mmol) per litre.

Typical early warning signs are feeling hungry, trembling or shakiness, and sweating. In more severe cases, you may also feel confused and have difficulty concentrating. In very severe cases, a person experiencing hypoglycaemia can 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.

Read more about the symptoms of hypoglycaemia

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 sandwich or a few biscuits.

If hypoglycaemia causes a loss of 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 the person giving the injection knows how to use it.

You should dial 999 to request an ambulance if:

  • a glucagon injection kit isn't available
  • there's nobody trained to give the injection
  • the injection is ineffective after 10 minutes

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

Read more about treating hypoglycaemia

Preventing hypoglycaemia

If you have diabetes that requires treatment with insulin, the safest way to avoid 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. You should be careful when drinking alcohol as it can also cause hypoglycaemia, sometimes many hours after drinking.

Exercise or activity is another potential cause, 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 insulin as the amount of insulin your body absorbs can differ depending on where it's 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 as the result of an underlying condition other than diabetes, the condition will need to be treated to prevent a further hypo.

Read more about preventing hypoglycaemia

Symptoms of hypoglycaemia

The symptoms of hypoglycaemia usually begin when your blood glucose level drops below four 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 regularly check your blood glucose levels.

Symptoms can vary from person to person, and it's important to be aware of the early warning signs so you can treat them.

Signs and symptoms of hypoglycaemia can include:

  • feeling hungry
  • sweating
  • dizziness
  • tiredness (fatigue)
  • blurred vision
  • trembling or shakiness
  • going pale
  • fast pulse or palpitations
  • tingling lips
  • irritability
  • difficulty concentrating
  • confusion
  • disorderly or irrational behaviour, which may be mistaken for drunkenness

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

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

For some people, the warning symptoms become greatly reduced, putting them at significant risk of having severe episodes where they're dependent on others for help.

Let your diabetes care team know if you develop this problem as your treatment may need to be changed to reduce the risk.

Read more about how hypoglycaemia is treated

Hypoglycaemia while sleeping

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

Although some people find their sleep is disturbed when they experience nocturnal hypoglycaemia, you may only notice the symptoms when you wake up in the morning.

The symptoms of nocturnal hypoglycaemia can include:

  • headache – 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 affects people with diabetes, although more rarely it can also occur as a result 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's commonly used to treat type 1 diabetes and is also recommended for some people with type 2 diabetes.

A fall in blood glucose levels can also occur after taking 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 how much insulin you inject, the amount of food you eat, and how much energy you burn during exercise.

Hypoglycaemia may occur if you've 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, don't eat enough carbohydrate, or exercise more than usual.

People with diabetes who've drunk too much alcohol, or drank alcohol on an empty stomach, can also get hypoglycaemia.

However, it's not always possible to identify why a particular episode of hypoglycaemia has occurred, and sometimes it happens 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 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's not clear why this happens, although it's 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 possible causes

Other possible causes of hypoglycaemia in people without diabetes are:

  • fasting or malnutrition – where not enough nutrients are consumed for your body to function properly
  • binge drinking or heavy drinking of alcohol
  • Addison's disease – a disorder of the adrenal glands (two small glands that sit on top of the kidneys) 
  • 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, you can treat hypoglycaemia yourself when you recognise the symptoms.

Treating an episode of hypoglycaemia

The immediate treatment for hypoglycaemia is to have some sugary food or drink (about 15 to 20g of rapidly acting carbohydrate) to end the attack.

For example, this could be:

  • 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 the sugar they do contain may 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 around 15 minutes to recover from a mild episode of hypoglycaemia. If you have a blood glucose meter, measure your blood sugar again after 15 to 20 minutes. If it's still too low (below 4mmol), you should have some more sugary food or a drink before testing your levels again in another 15 to 20 minutes.

When treating someone else with hypoglycaemia, if the above treatment isn't effective, you may be able to help them by applying glucose gel (or honey, treacle or jam if glucose gel isn't available) to the inside of their cheeks, and gently massaging the outside of their cheeks.

It may take 10 to 15 minutes before they feel better. This shouldn't 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 team to find out the underlying cause. Your medication may need to be 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 given an injection of the hormone glucagon (if they have an injection kit). The injection will raise their blood glucose level.

The injection should be carried out by a friend or family member who knows what they're doing, or by a trained healthcare professional.

You should dial 999 to request an ambulance if:

  • a glucagon injection kit isn't available
  • there's nobody available who's trained to give the injection
  • the injection is ineffective after 10 minutes

Never try to put food or drink into the mouth of someone who's unconscious as they could choke.

If you're 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.

Preventing hypoglycaemia

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

It's also important to monitor your blood glucose levels.

Monitoring blood glucose

Regularly monitoring your blood glucose levels can help you keep your blood glucose as normal and stable as possible, and will help you spot the signs and symptoms of hypoglycaemia quickly.

Your blood glucose level can vary throughout the day, so you may need to check it several times a day, depending on the treatment you're taking.

You can monitor your blood glucose levels using a blood glucose meter, a small device that measures the concentration of glucose in your blood.

Read more about living with type 1 diabetes and living with type 2 diabetes

Food and 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're taking insulin, your doctor may advise you to lower 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, it's recommended that you drink no more than 2 to 3 units of alcohol a day and eat a snack after drinking alcohol.

Spotting the signs

As hypoglycaemia can develop suddenly, it's important to be aware of the symptoms of hypoglycaemia so you can treat it quickly. Tell your family and friends about the signs to look out 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 they can be helped quickly and efficiently.

Keep treatment with you

If you're 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. This can be used to treat hypoglycaemia that doesn't respond to normal treatment.

If you're being treated with insulin, you'll usually be given a kit that contains an injection of a medication called glucagon. Family members 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 it 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 that requires 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, pull over and stop as soon as it's safe to do so. Remove the keys from the ignition and get out of the driver's seat before treating hypoglycaemia in the normal way.

If you have two or more episodes of hypoglycaemia that require assistance in a 12-month period, it's a legal requirement to stop driving and inform the DVLA.

If you're a group two driver (you hold a licence to drive buses, coaches or lorries), you're legally required to stop driving group two vehicles immediately and inform the DVLA if you have a single episode of hypoglycaemia that requires assistance.

Inform your diabetes care team if you start having problems recognising hypoglycaemia or you start to have more regular episodes, even if there were warning symptoms and you were able to treat them without assistance.

See the GOV.UK website for more information about hypoglycaemia and driving

Last updated:
20 February 2023