Low blood pressure (hypotension)

Low blood pressure (hypotension) is when your blood pressure falls much lower than is normal for you. When this happens, low blood pressure symptoms may include dizziness and fainting.

About low blood pressure

Blood pressure is a measure of the force that your blood puts on the walls of your arteries as they pump blood around your body. You’ll see your blood pressure shown as two numbers – for example, 120/80mmHg. The letters mmHg stand for millimetres of mercury, which is the unit used to measure blood pressure.

• 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.

There’s no set level at which your blood pressure is said to be too low – it’s different for everyone. You may have blood pressure that’s naturally lower than the average blood pressure range (between 90/60 mmHg and 120/80 mmHg). 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 causes symptoms.

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 have these problems. But if your blood pressure gets much lower than is usual for you, it can cause fainting, falls and accidents.

For more information, see our section on symptoms of low blood pressure.

Causes of low blood pressure

Lots of things can make your blood pressure drop lower than usual. These include the following.

• Loss of fluid. This might happen from losing a lot of blood, or from severe vomiting and diarrhoea, or from sweating a lot due to vigorous exercise.
• Problems with your heart that could mean it can’t pump as much blood around your body.
• Diseases that affect your autonomic nervous system. This system regulates your blood pressure; it can be affected by certain conditions including Parkinson’s disease and both type 1 and type 2 diabetes.
• Side-effects of some medicines. Medicines that can affect your blood pressure include some for high blood pressure, heart disease and depression.
• Severe infection – for example, sepsis.
• Reflex syncope. This is a quick but temporary drop in your blood pressure, which makes you to lose consciousness (faint) briefly. It can happen for reasons such as standing for a long time, being in pain or having emotional stress and fear.
• Pregnancy. A drop in blood pressure can be part of the normal changes that happen to your body in pregnancy. For more information, see our section on pregnancy and low blood pressure.

Sometimes, your blood pressure only drops when you stand up because blood has pooled in your legs. This is called postural or orthostatic hypotension and can be triggered by things listed above. But it’s also more common in older people. The systems in your body that regulate your blood pressure may not work so well as you get older. Postural hypotension usually lasts for only a short time and causes very temporary (just seconds) of dizziness.

You may get postural hypotension after you eat a meal, especially one that is high in carbohydrates. This is called postprandial hypotension.

Pregnancy and low blood pressure

It’s normal for your blood pressure to get 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, and will return 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. Make sure you get up slowly from lying or sitting down. If you feel you’re going to faint, sit or lie down right away.

If you lie flat on your back in late pregnancy, your womb (uterus) can press down on a large vein that carries blood to your heart from other parts of your body. This can cause low blood pressure and make you feel faint, so try to lie on your side in late pregnancy.

Occasionally, symptoms of low blood pressure may be caused by other health conditions that affect 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 low blood pressure symptoms. These may include:

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

You might only have these low blood pressure symptoms when you stand up after sitting or lying down (postural or orthostatic hypotension). But this might 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: Having your blood pressure taken.

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 your blood pressure is much lower when you stand up than when you’re sitting down, this suggests you have postural hypotension.

Your GP may also recommend that you have:

• blood tests to check your general health
• an electrocardiogram (ECG)to check the electrical activity of your heart
• an echocardiogram (ultrasound of your heart) if they need to check for any problems that affect your heart

If your symptoms need further investigation, your doctor may recommend you have a tilt test. In a tilt test, you lie on a table that’s gradually tilted until it’s nearly upright. Your blood pressure and heart rhythm and rate are monitored while the table is tilting. You’ll be in the tilted position for between 15 and 45 minutes.

Your GP may refer you to a doctor who specialises in heart problems (cardiologist) if they can’t find a cause for your low blood pressure. Or they may refer you if they think you may have a problem with your heart.

Self-help for low blood pressure

If you have low blood pressure, you can take some steps to help prevent or reduce your symptoms.

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

• Stand up slowly after sitting down, especially when you first wake up. If you’re lying down, sit for a while before you stand up.
• Take care when you get out of hot baths or showers. It may be best not to have very hot baths.
• Drink enough fluid to keep hydrated (around 1 and a half to 2 litres per day).
• If you drink alcohol, don’t drink to excess.
• If possible, raise 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 you eat:

• eat smaller meals, more often
• eat foods that don’t contain too much carbohydrate (such as rice, bread and pasta)
• don’t stand up suddenly after a meal

If you faint because of low blood pressure, think about any possible triggers and whether you can avoid or manage them. This may include not standing still for long periods or not going into warm environments.

If you feel faint, immediately sit or lie down if you can do so safely. Put your feet up so that they’re higher than the level of your heart. If you can’t sit or lie down:

• squat down
• cross your legs
• tense the muscles in your legs and arms

If your symptoms don’t go away, seek medical attention.

Treatment for low blood pressure

Low blood pressure treatment aims to increase your blood pressure so you don’t get any symptoms and won’t be at risk of falling over.

Your GP will discuss some simple things you can do to help yourself. For more information on this, see our section on self-help for low blood pressure.

Your GP may also suggest you:

• increase the amount of salt in your diet – only do this if your doctor suggests it because it may affect other health conditions you have
• wear compression stockings if you have postural hypotension (low blood pressure when you stand up) – these stockings can help stop blood from pooling in your legs

Medicines

Some medicines can cause low blood pressure, including those taken for high blood pressure. Your GP may review your medicines to see if any of these could be causing your low blood pressure or making your symptoms worse. They may suggest you stop or change your medicines to see if this helps. But don’t stop or change any of your medicines without discussing it with your GP first.

Doctors don’t usually prescribe medicines to treat low blood pressure because these medicines can cause side-effects. But your GP or a specialist may prescribe medicines if self-help measures don’t stop your symptoms of low blood pressure. This may include medicines that:

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

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 for you.