Low blood pressure (hypotension)

Low blood pressure, also known as hypotension, is where blood pressure in your arteries is abnormally low.

Introduction

Low blood pressure, also known as hypotension, is where blood pressure in your arteries is abnormally low.

Naturally low blood pressure is unlikely to cause any symptoms and is normally nothing to worry about. However, if your blood pressure drops too low, it can restrict the amount of blood flowing to your brain and other vital organs, which can cause, unsteadiness, dizziness, lightheadedness or fainting.

Read more about the symptoms of low blood pressure.

See your doctor if you experience any symptoms of low blood pressure and are concerned.

All adults should have their blood pressure checked at least every five years. If you haven't had yours measured or don't know what your reading is, ask your doctor to check it.

What is low blood pressure?

The heart pumps a constant supply of blood around the body through arteries, veins and capillaries. Blood pressure is a measure of the force of the blood on the walls of the arteries as the blood flows through them.

It is measured in millimetres of mercury (mmHg) and recorded as two measurements:

  • systolic pressure - the pressure when your heart beats and squeezes blood into your arteries
  • diastolic pressure - the pressure when your heart rests between beats

For example, if your systolic blood pressure is 120 mmHg and your diastolic blood pressure is 80 mmHg, your blood pressure is 120 over 80, which is commonly written as 120/80.

Normal blood pressure is between 90/60 and 140/90. If you have a reading of 140/90 or more, you have high blood pressure (hypertension), which puts you at greater risk of developing serious health conditions, such as heart attack or stroke.

People with a blood pressure reading of around 90/60 or less are usually regarded as having low blood pressure.

Read more about diagnosing low blood pressure.

Why do I have low blood pressure?

You can have low blood pressure for many reasons, including the time of day, your age, the temperature, any medication you may be on, an injury and some illnesses.

Read more about the causes of low blood pressure.

Treatment and self-help

Naturally low blood pressure does not usually need to be treated unless it is causing symptoms such as dizziness or recurrent falls. If it is causing symptoms, your doctor will look at what the cause might be in case it can be treated.

There are also various things you can do to help limit symptoms of low blood pressure, including:

  • standing up gradually and avoiding standing for long periods of time
  • ensuring you are well hydrated
  • wearing support stockings
  • avoiding caffeine at night and limiting your alcohol intake
  • eating more salt in your diet
  • eating smaller meals, more often

Read more about treating low blood pressure.

Symptoms

If your blood pressure is naturally low, it's unlikely it will cause you any symptoms or require treatment.

However, low blood pressure can sometimes mean there's not enough blood flowing to your brain and other vital organs, which can lead to symptoms such as:

  • dizziness
  • lightheadedness
  • unsteadiness, or feeling of loss of balance
  • fainting
  • blurred vision
  • a rapid, or irregular heartbeat (palpitations)
  • confusion
  • feeling sick (nausea)
  • general weakness

If you experience symptoms of low pressure after changing positions, such as standing up, it is known as postural, or orthostatic, hypotension.

Symptoms shouldn't last longer than a few seconds as your blood pressure will adjust to your new position. This type of low blood pressure tends to affect people more as they get older, when it can lead to more frequent falls. Similar symptoms may also occur after exercise.

If you experience symptoms after eating, it's known as postprandial hypotension and occurs more often in older people, particularly in those who have high blood pressure or conditions such as Parkinson's disease and diabetes.

After a meal, your intestines need a large amount of blood for digestion. If your heart rate does not increase enough to maintain blood pressure, your blood pressure will fall, causing symptoms.

Some people experience symptoms after standing up for long periods of time. This is sometimes known as neurally mediated hypotension and most often affects children and young adults.

Read more about causes of low blood pressure.

What to do if you have symptoms

If you think you may be experiencing an episode of low blood pressure you should:

  • stop what you're doing
  • sit or lie down
  • drink some water

The symptoms will usually pass after a few seconds or minutes.

When to see your doctor

You should see your doctor if you have frequent symptoms of low blood pressure. Your doctor can measure your blood pressure and help identify any underlying causes of the problem.

Read more about diagnosing low blood pressure.

Causes

Throughout the day, it is normal for your blood pressure to vary depending on what you are doing.

Stress at work, the temperature outside and your diet could all affect your blood pressure reading.

Each time you have your blood pressure measured, it's important the test is carried out under similar conditions to ensure results are consistent. If you have a low blood pressure reading, your doctor will first consider everyday causes that might have affected it, before considering possible underlying causes.

Everyday causes

Many factors have a daily, or even hourly, effect on your heart and circulation. Below are things that could affect your blood pressure and, in some cases, may cause low blood pressure.

  • The time of day - your blood pressure falls overnight and rises during the day.
  • Your age - your blood pressure usually increases as you get older, but a drop in blood pressure from movement or eating is more common with age.
  • How stressed or relaxed you are - you have lower blood pressure the more relaxed you are.
  • How much exercise you do - initially, exercise will raise your blood pressure, but if you are healthy and exercise regularly, your blood pressure will be low when you are resting.
  • Temperature - a warm temperature may cause your blood pressure to fall.
  • If you have recently eaten - blood will be used for digesting food in your stomach, so the blood pressure elsewhere in your body will fall.

Underlying causes

If your blood pressure is still considered low after taking into account everyday factors, such as those listed above, there may be another cause. Some possibilities are explained below.

Medication

Some types of medication may cause low blood pressure, including the following:

  • blood pressure lowering medication
  • beta-blockers - medicine that may be prescribed for a problem with your heart
  • alpha-blockers - medicine prescribed to lower blood pressure for people with high blood pressure (hypertension and those with prostate gland problems (the prostate is a small gland only found in men located between the penis and bladder)
  • some antidepressants

Your doctor will discuss possible side effects with you when prescribing medication and your blood pressure will be carefully monitored if you are considered to be at risk of hypotension.

Dehydration

Dehydration can occur if fluid is lost, either through skin from excessive sweating in hot weather, or from the gastrointestinal tract as a result of vomiting or diarrhoea.

Serious illness or conditions

If you have a short-term (acute) illness, your blood pressure will be measured regularly as it is a good indicator of how severe your illness is. A heart condition, such as heart disease or a heart attack, can also cause low blood pressure because your heart may not be able to pump blood around your body.

Neurological disorders

Neurological disorders, such as Parkinson’s disease, are conditions affecting your nerves. Low blood pressure can occur if part of your nervous system called the autonomic nervous system is affected.

Your autonomic nervous system is the part of your nervous system that controls bodily functions you do not actively think about, such as sweating and digestion. It also controls the widening and narrowing of your blood vessels.

If there is a problem with your autonomic nervous system, your blood vessels could remain too wide, and this can cause low blood pressure.

Hormone problems Having a condition that affects production of certain hormones in your body, such as diabetes](yourmd:/condition/diabetes/diabetes) or [Addison's disease, can also cause low blood pressure.

Addison's disease is where the immune system attacks and damages the adrenal glands, which are two small glands located just above your kidneys. They produce hormones that control your blood pressure and maintain the balance of salt and water in your body.

Low blood pressure can also occur if your adrenal glands become damaged, for example because of an infection or a tumour.

Serious injury and shock

Low blood pressure can be caused by serious injuries or burns, particularly if you lose a lot of blood. Low blood pressure can also occur if you go into shock after having a serious injury.

Septic shock and toxic shock syndrome

Septic shock and toxic shock syndrome are caused by bacterial infections. Bacteria attack the walls of the small blood vessels, causing them to leak fluid from the blood into the surrounding tissues. This causes a significant drop in blood pressure.

Anaphylactic shock

Anaphylactic shock, or anaphylaxis, is caused by an allergic reaction. During an allergic reaction, your body produces a large amount of a chemical called histamine, which causes your blood vessels to widen, leading to a sudden, severe drop in blood pressure.

Cardiogenic shock

Cardiogenic shock occurs when your heart cannot supply enough blood to your body, leading to a drop in blood pressure. This can happen during a heart attack.

Other causes

Other possible causes of low blood pressure are listed below.

  • miscommunication between the heart and brain - low blood pressure that occurs after standing for long periods of time (neurally mediated hypotension) happens when your body tells the brain your blood pressure is too high, when it's actually too low; this causes your brain to slow down the heartbeat, further reducing your blood pressure
  • anaemia - a condition where the amount of haemoglobin in the blood is below the normal level, or there are fewer red blood cells than normal
  • prolonged bed rest
  • your genes - some research has suggested that low blood pressure is genetic. If your parents have low blood pressure, it is possible you could inherit it from them

In some cases, there is no obvious cause of low blood pressure.

Diagnosis

Low blood pressure (hypotension) can be easily diagnosed by measuring your blood pressure.

A blood pressure reading is taken using two measurements. The first is known as systolic, which is the pressure in your arteries when your heart contracts and pushes blood around your body.

The second measurement is known as diastolic, which is the pressure in your arteries when your heart refills with blood in between heartbeats. Both systolic and diastolic blood pressures are measured in millimetres of mercury (mmHg).

How blood pressure is measured

Blood pressure is often measured using a sphygmomanometer, a device which consists of a stethoscope, arm cuff, dial, pump and valve.

The cuff is placed around your arm and pumped up to restrict the blood flow. The pressure is then slowly released as your pulse is checked using the stethoscope.

Hearing how your pulse beats after the cuff is released allows a measurement to be taken on the mercury scale, giving an accurate reading of your blood pressure.

Many doctor surgeries now use digital sphygmomanometers, which measure your pulse using electrical sensors.

Before having your blood pressure taken, you should rest for at least five minutes and empty your bladder.

To get an accurate blood pressure reading, you should be sitting down and not talking when the reading is taken.

After you have had your blood pressure taken, your doctor or nurse will give you your systolic reading first followed by your diastolic reading. If your systolic blood pressure is 120 mmHg, and your diastolic blood pressure is 80 mmHg, you will be told that your blood pressure is 120 over 80, written as 120/80.

Low blood pressure

As a general guide, low blood pressure is a reading below 90/60.

If you have low blood pressure according to this guide, you do not need to worry. Naturally low blood pressure rarely causes symptoms or needs treating. Having low blood pressure is considered healthy because it protects you from the risks and diseases of high blood pressure.

Postural or orthostatic hypotension

If your symptoms of low blood pressure mostly occur when you change position (postural or orthostatic hypotension), your blood pressure may be measured before and after you move. For example, your blood pressure may be measured while you are sitting down and again while you are standing up.

Depending on what your seated blood pressure is, if your systolic reading falls by between 15 to 30 mmHg when you stand up, you may have orthostatic hypotension.

Identifying underlying causes

Your doctor or practice nurse will usually be able to diagnose low blood pressure very easily. However, determining the reason for low blood pressure can often be more difficult.

If you have an underlying condition causing low blood pressure, it is likely you will have other symptoms as well. You should discuss these with your doctor, who may recommend further tests.

Further tests may include blood tests to check for anaemia and measurements taken of your hormone levels or blood sugar (glucose) level, or an electrocardiogram (ECG) to detect any irregularities in your heart rhythm.

Treatment

Low blood pressure (hypotension) usually only needs to be treated if it is causing symptoms. This will involve general lifestyle advice and treating any underlying cause of the condition.

If you have naturally low blood pressure and it's not causing any problems, treatment is rarely necessary.

General advice

The advice outlined below can often help limit symptoms of some of the most common types of hypotension:

  • Stand up gradually - particularly first thing in the morning. It may also be useful to try other physical movements first to increase your heart rate and the flow of blood around your body. For example, stretching in bed before you get up or crossing and uncrossing your legs if you are seated and about to stand.
  • Avoid standing for long periods of time - this can help prevent neurally mediated hypotension (low blood pressure caused by miscommunication between heart and the brain).
  • Wear support stockings - sometimes called compression stockings, these are tight-fitting elastic socks or tights. They provide extra pressure to feet, legs, and abdomen, which can help improve circulation and increase blood pressure. However, you should speak to your doctor before using support stockings because they are not suitable for everyone.
  • Avoid caffeine at night, and limit your alcohol intake - this can help you to avoid becoming dehydrated, which can also cause low blood pressure.
  • Eat small, frequent meals rather than large ones - this can help prevent postprandial hypotension (low blood pressure after eating). Lying down after eating or sitting still for a while may also help.

Increasing your fluid and salt intake

Dehydration can cause low blood pressure. This can be easily treated by increasing your fluid and salt intake. Ensuring you drink enough fluid will help by increasing the volume of your blood, which will increase your blood pressure.

If you have low blood pressure, you may benefit from having more salt in your diet. Your doctor will be able to advise how much additional salt you need and whether you can add salt to your usual food or if you need to take salt tablets. Don't add extra salt to your diet without seeing your doctor first.

Changing your medication

If your doctor suspects your medication is causing low blood pressure, they may advise using an alternative medication or may alter your dose.

Your blood pressure should be monitored while you're taking medication and changes noted. Tell your doctor if you are experiencing side effects from taking medication.

Treating underlying conditions

If your doctor suspects your low blood pressure is being caused by an underlying health condition, you may be referred to hospital for further tests and treatment.

For example, if your low blood pressure is related to hormone problems (see causes of low blood pressure for more information), you may be referred to a specialist called an endocrinologist who may prescribe hormone replacement medication.

Medication for low blood pressure

Very few people are prescribed medication for low blood pressure. The symptoms of hypotension can usually be treated by making the above changes to your lifestyle and, in particular, by increasing your fluid and salt intake.

If medication is necessary, it will usually be medicines to expand the volume of your blood or to constrict (narrow) your arteries. By increasing your blood, or decreasing your arteries, your blood pressure will increase because there will be more blood flowing through a smaller space.

Content supplied by NHS Choices