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Low blood pressure (hypotension)


Expert reviewer, Dr Tim Cripps, Consultant Cardiologist
Next review due January 2024

Low blood pressure (hypotension) is when your blood pressure falls much lower than is normal for you. When this happens, it can cause symptoms such as dizziness and fainting.



About low blood pressure

Your blood pressure is a measure of the force that your blood puts on the walls of your arteries as it's pumped around your body. You’ll see blood pressure shown as two numbers such as 120/80mmHg. The first number is the highest pressure when your heart contracts – this is your systolic blood pressure. The second number is the pressure when your heart is fully relaxed – this is your diastolic blood pressure. The letters mmHg stand for millimetres of mercury, which is the unit used to measure blood pressure.

There’s no set level at which your blood pressure is said to be too low – it’s different for everyone. You might have a blood pressure that’s naturally lower than average – but if it doesn’t cause you any problems, it won’t be classed as ‘low blood pressure’. Your blood pressure is usually only considered to be too low if it’s causing symptoms.

Causes of low blood pressure

There are lots of things that can cause your blood pressure to drop lower than normal. These include the following.

  • Loss of fluid – for example, from losing a lot of blood, severe vomiting and diarrhoea, or sweating a lot due to vigorous exercise.
  • Problems with your heart, which means it can’t pump as much blood around your body.
  • Diseases that affect your autonomic nervous system, which normally regulates your blood pressure – including Parkinson’s disease and diabetes.
  • Side-effects of some medicines, including some for high blood pressure, heart disease and depression.
  • Severe infection, or a severe allergic reaction.
  • Reflex syncope – there are certain things that can cause a quick but temporary drop in your blood pressure, causing you to lose consciousness (faint) briefly. These can include standing for a long time, pain, emotional stress and fear.
  • Pregnancy – a drop in blood pressure can be part of the normal changes that happen to your body. See ‘pregnancy and low blood pressure’ for more information.

Sometimes, your blood pressure only drops when you stand up, causing blood to pool in your legs. This is called postural or orthostatic hypotension. It can be triggered by the factors listed above, but is also more common as you get older. This is because the systems in your body that normally regulate your blood pressure start to decline with age.

You may also be more likely to get postural hypotension after eating a meal, especially one high in carbohydrates. This is known as postprandial hypotension.

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Pregnancy and low blood pressure

It’s normal for your blood pressure to become lower during pregnancy. This is mainly because your hormones relax the walls of your blood vessels. Your blood pressure may fall very early in your pregnancy and reach its lowest point during your second trimester (weeks 13 to 28). It then starts to rise again, returning to normal after you have your baby.

If you have low blood pressure during pregnancy, you may feel faint and dizzy suddenly when you get up from lying or sitting down. This is called postural hypotension. You can help relieve your symptoms by making sure you get up slowly from lying or sitting. And if you feel you’re going to faint, sit or lie down right away.

Occasionally, symptoms of low blood pressure may be caused by other underlying health conditions affecting your pregnancy. Always tell your midwife about your symptoms. Seek medical help if you have dizziness or fainting or any other symptom that you’re worried about.

Symptoms of low blood pressure

If your blood pressure is naturally quite low, you’re unlikely to have any symptoms and it's not something to worry about.

However, if your blood pressure becomes lower than usual for you, it can cause symptoms such as:

  • dizziness or light-headedness
  • fainting
  • palpitations (you can feel your heart beating more forcefully)
  • feeling sick
  • blurred vision
  • feeling tired or weak

You might only have these symptoms when you stand up from sitting or lying down, (postural or orthostatic hypotension). This might even make you fall over.

If you keep having symptoms like these, contact your GP.

If your blood pressure drops very quickly or suddenly, for instance, if you’ve lost a lot of blood, this can lead to shock. This is an emergency situation: you’ll feel and look very unwell and will need to call for medical help straightaway.

Diagnosis of low blood pressure

Your GP will ask about your symptoms and examine you. They’ll measure your blood pressure using either an automated digital device or a manual device. To find out more about how blood pressure is measured, see our animation at the top of this page, Having your blood pressure taken, in the introduction above.

If you have symptoms of postural hypotension (low blood pressure when you stand up), your GP may also measure the change in your blood pressure while you’re sitting (or lying) and then standing. If it’s much lower when you stand up compared with when you’re sitting down, this suggests you have postural hypotension.

Your GP may also recommend that you have some blood tests to check your general health and an electrocardiogram (ECG) to check the electrical activity of your heart. They may also ask you to have an echocardiogram (ultrasound of your heart) if they need to check for any underlying problems affecting your heart.

If your symptoms need further investigation, your doctor may recommend that you have a tilt test. The test involves being slowly tilted from lying down to an upright position on a table as your blood pressure, heart rate and rhythm are monitored. For more information, see our FAQ: What happens in a tilt test? below.

Self-help for low blood pressure

There are some simple steps you can take to help prevent or reduce your symptoms.

If you have postural hypotension (get symptoms when you stand up), the following may help.

  • Stand up slowly from sitting or lying down, especially when you first wake up. If you’re lying down, sit for a while first before standing.
  • Take care getting out of hot baths or showers. It may be best to avoid very hot baths.
  • Make sure you drink enough fluid to keep hydrated.
  • If you drink alcohol, don’t drink to excess.
  • If you can, try raising the head of your bed a little.
  • When you stand up, it may help to cross your legs, stand on tiptoes or tense your muscles.
  • Try to keep physically active.
  • If you get symptoms after eating, eat smaller, more frequent meals, that don’t contain too much carbohydrate (such as rice, bread and pasta), and avoid standing suddenly after a meal.

If you’re fainting because of low blood pressure, it can help to think about what situations tend to set this off, and how you may be able to avoid or manage these. This might include not standing still for long periods or avoiding warm environments.

If you feel faint, you should immediately sit or lie down if you can do so safely. Put your feet up so that they are higher than the level of your heart. If you can’t sit or lie down, it may help if you can squat down, or at least cross your legs and tense the muscles in your legs and arms. If your symptoms don’t go away, seek medical attention.

Treatment for low blood pressure

Your GP will go through some simple things you can do to help yourself – see the section on self-help above for more information. They may also suggest you increase the salt in your diet. Don't do this unless your doctor suggests it, as it may affect other health conditions you have.

Your GP may also suggest you wear compression stockings if you have postural hypotension (low blood pressure when you stand up). These can help stop blood from pooling in your legs.

Medicines

Sometimes, low blood pressure can be caused by the medicines you’re taking. Your GP may review your medicines to see if there are any that could be making your symptoms worse or bringing them on. They may suggest stopping or changing your medication to see if that helps. It’s important that you don’t stop or change any of your medicines without discussing it with your GP first.

Your GP or a specialist may prescribe medicines if self-help measures don’t stop your symptoms of low blood pressure. These may include medicines that:

  • control the amount of salts and fluids in your body
  • make your veins constrict (get smaller), increasing your blood pressure

You may need treatment for any underlying health condition that’s causing your low blood pressure. If so, your GP will discuss with you what’s best in your particular circumstances.

Frequently asked questions about low blood pressure

  • Low blood pressure is when your blood pressure falls much lower than is normal for you. This can cause symptoms such as dizziness and fainting.

  • In a tilt test, you lie on a table which is gradually tilted until it’s nearly upright, while your blood pressure and heart rhythm and rate are monitored. Safety belts will be placed around your body to keep you secure. You’ll only be in the tilted position for between 15 and 45 minutes.

    If you start to get symptoms, such as feeling light-headed, dizzy or faint, the doctor will record any change in your blood pressure or heart rate, and stop the test. You can also ask for it to stop at any time. At the end of the test, the table will be returned to a flat position to allow you to recover before you go home.

  • Both type 1 and type 2 diabetes can damage your nerves. This is called diabetic neuropathy. Diabetic neuropathy can affect the nerves to your blood vessels in your legs, preventing them from getting the message to constrict (narrow) when you stand up. This means that blood pools in your legs, reducing the amount that reaches your brain and causing symptoms such as fainting and dizziness. This is called postural hypotension.

  • As long as it’s not causing any problems, the lower your blood pressure, generally the better. High blood pressure is a risk to your health – it can lead to serious conditions such as stroke, coronary heart disease and kidney failure. The lower your blood pressure, the less likely you are to suffer from these problems.

    However, if your blood pressure becomes lower than usual for you, it can cause problems. If you have any symptoms like feeling dizzy or faint, you should contact your doctor. See the symptoms sections above for more information.



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Related information

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  • Reviewed by Pippa Coulter, Freelance Health Editor, January 2021
    Expert reviewer, Dr Tim Cripps, Consultant Cardiologist
    Next review due January 2024

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