Low Blood Pressure (Hypotension): Symptoms, Causes and What to Do

Blood pressure naturally varies throughout the day, and having a relatively low blood pressure is not necessarily a health problem.

However, when blood pressure becomes too low and causes symptoms such as dizziness, weakness, blurred vision or fainting, it may need further investigation.

Low blood pressure is also known as hypotension.

The NHS generally defines low blood pressure as a reading below 90/60 mmHg.

Some people naturally have blood pressure around or below this level without experiencing any symptoms. For others, low blood pressure may be related to dehydration, medicines, pregnancy or an underlying medical condition.

Understanding the difference is important.

What Do Blood Pressure Numbers Mean?

A blood pressure reading contains two numbers and is measured in millimetres of mercury (mmHg).

For example:

90/60 mmHg

The first number is your systolic blood pressure. It measures the pressure in your arteries when your heart contracts and pumps blood.

The second number is your diastolic blood pressure. It measures the pressure in your arteries between heartbeats.

A reading below 90/60 mmHg is generally considered low blood pressure.

However, the number alone does not determine whether you need treatment.

If you feel well and your blood pressure is naturally low, treatment may not be necessary.

What Are the Symptoms of Low Blood Pressure?

Many people with low blood pressure experience no symptoms.

When symptoms do occur, they can include:

• lightheadedness or dizziness,
• feeling sick,
• blurred or fading vision,
• weakness,
• tiredness,
• confusion, and
• fainting.

Repeated dizziness or fainting should not simply be ignored.

Speak to a healthcare professional if you regularly experience these symptoms.

What Causes Low Blood Pressure?

There are many possible causes.

Sometimes low blood pressure is normal for that particular person.

In other cases, it can be caused by a temporary situation, medication or medical condition.

1. Dehydration

Not having enough fluid in your body can reduce blood volume and contribute to low blood pressure.

Dehydration can occur because of inadequate fluid intake, vomiting, diarrhoea, excessive sweating or certain illnesses.

2. Medicines

Some medicines can lower blood pressure.

These include some medicines used for:

• high blood pressure,
• heart conditions,
• depression, and
• removing excess fluid from the body, such as diuretics.

Other medicines and some over-the-counter or herbal products can also affect blood pressure.

If you think a medicine is making your blood pressure too low, do not stop taking it by yourself.

Speak to your doctor or pharmacist.

The dose may need reviewing, or another treatment may be more appropriate.

3. Pregnancy

Blood pressure can be lower during pregnancy.

This is relatively common and is not necessarily a cause for concern.

However, significant dizziness, fainting or other concerning symptoms during pregnancy should be discussed with an appropriate healthcare professional.

4. Medical Conditions

Certain medical conditions can contribute to low blood pressure.

Examples include:

• diabetes,
• heart failure,
• abnormal heart rhythms,
• thyroid problems, and
• Parkinson's disease.

Finding and treating the underlying condition may improve the blood pressure problem.

5. Blood Loss

Significant blood loss reduces the amount of blood circulating through the body.

Severe bleeding can therefore cause a dangerous fall in blood pressure and requires urgent medical attention.

6. Severe Infection or Allergic Reaction

Dangerously low blood pressure can occur during medical emergencies such as severe infection or anaphylaxis.

This is very different from someone who naturally has a blood pressure around 90/60 mmHg and feels completely well.

Severe illness accompanied by collapse, breathing difficulties, confusion or other emergency symptoms requires immediate medical attention.

What Is Postural Hypotension?

Some people become dizzy or lightheaded when they stand up after sitting or lying down.

This can happen because their blood pressure falls when they change position.

It is called postural hypotension, also known as orthostatic hypotension.

NICE recommends checking blood pressure while lying down, or sitting if necessary, and then checking it again after standing for at least one minute when postural hypotension is suspected.

A fall of at least 20 mmHg in systolic pressure or 10 mmHg in diastolic pressure after standing is considered significant and should prompt consideration of possible causes, including medicines.

Postural hypotension can increase the risk of falls, particularly in older people.

What Should You Do If You Feel Dizzy When Standing?

Move slowly.

When getting out of bed:

1. Move from lying down to sitting.
2. Sit for a short time.
3. Stand carefully.
4. Hold onto something stable if necessary.

Avoid suddenly jumping out of bed or rapidly changing position if this regularly makes you dizzy.

If you repeatedly experience dizziness when standing, discuss it with your GP.

How Is Low Blood Pressure Diagnosed?

Blood pressure can be checked:

• at home using an appropriate blood pressure monitor,
• at some pharmacies,
• by a nurse, or
• by your GP or another healthcare professional.

One isolated low reading does not necessarily establish that you have a medical problem.

Your healthcare professional may consider:

• your symptoms,
• repeated blood pressure readings,
• medicines you take,
• existing medical conditions, and
• whether your blood pressure changes when you stand.

Further tests may sometimes be required to identify the cause.

How Can You Manage Symptoms of Low Blood Pressure?

Treatment depends on why your blood pressure is low.

If there is an underlying cause, treating that cause is usually more important than simply trying to make the blood-pressure number higher.

However, several measures may help some people.

Get Up Slowly

Move gradually when going from lying to sitting and from sitting to standing.

This can be particularly useful for people with postural hypotension.

Drink Enough Fluid

Dehydration can contribute to low blood pressure.

Maintaining adequate hydration may therefore help when dehydration is part of the problem.

However, do not automatically increase your fluid intake if a healthcare professional has told you to restrict fluids, for example because of certain heart or kidney conditions.

Ask for individual advice.

Avoid Standing Still for Long Periods

Some people find that standing still for a long time worsens their symptoms.

Regular gentle movement may help circulation.

Consider Smaller, More Frequent Meals

Some people experience a drop in blood pressure after eating.

Smaller meals more frequently may help reduce symptoms in some cases.

Limit Excessive Alcohol

Alcohol can contribute to dehydration and may worsen low-blood-pressure symptoms.

If you notice that alcohol makes you dizzy or lightheaded, reducing your intake may help.

Should You Eat More Salt for Low Blood Pressure?

Do not automatically start adding large amounts of salt to your diet because you have a low blood-pressure reading.

Although increasing salt can raise blood pressure and may occasionally be recommended for certain people with symptomatic hypotension, excessive salt can be harmful for others.

This is especially important for people with high blood pressure, heart disease, kidney problems or other medical conditions.

If increasing salt might be appropriate for you, discuss it with a healthcare professional first.

Can Compression Stockings Help?

Compression or support stockings may help some people with low blood pressure by reducing blood pooling in the legs and improving circulation.

However, they are not suitable for everyone.

Ask a healthcare professional whether compression stockings are appropriate before using them specifically to treat hypotension.

Are Medicines Used to Treat Low Blood Pressure?

Sometimes, but not usually.

The NHS says medicine specifically to increase blood pressure is rarely needed because lifestyle measures or treatment of the underlying cause are often sufficient.

For example, if medication is causing low blood pressure, a doctor may consider adjusting the medicine or its dose.

Never change prescribed medication without medical advice.

Is Low Blood Pressure Dangerous?

Not necessarily.

Some healthy people naturally have low blood pressure and experience no symptoms.

The concern increases when low blood pressure:

• causes repeated fainting,
• causes significant dizziness,
• increases the risk of falls,
• occurs suddenly,
• results from serious bleeding,
• occurs during severe infection or anaphylaxis, or
• is associated with another significant medical problem.

Therefore, the symptoms and underlying cause are often more important than the number alone.

Does Low Blood Pressure Cause High Blood Pressure?

No.

Hypotension and hypertension describe opposite blood-pressure problems.

Having an episode of low blood pressure does not mean that it will turn into high blood pressure.

A person's blood pressure can change over time for many reasons, but low blood pressure should not be described as a cause of hypertension.

Does Low Blood Pressure Cause a Heart Attack?

Low blood pressure should also not simply be described as causing a heart attack.

Very low blood pressure can occur in serious medical emergencies and can compromise blood flow to vital organs.

But this is very different from saying that ordinary low blood pressure automatically leads to a heart attack.

A person with naturally low blood pressure and no symptoms should not be frightened into believing that a heart attack is inevitable.

When Should You See a GP?

See a GP if you repeatedly experience symptoms associated with low blood pressure, particularly:

• dizziness,
• lightheadedness,
• fainting,
• blurred vision,
• weakness, or
• confusion.

It is especially important to seek medical advice if symptoms are new, worsening or interfering with everyday life.

Your GP can investigate whether medicines, dehydration or another medical condition may be contributing.

When Is It an Emergency?

A mildly low blood-pressure reading without symptoms is very different from a sudden collapse or severe illness.

Call 999 in the UK for a medical emergency, particularly if someone:

• has collapsed and is not recovering normally,
• has severe difficulty breathing,
• develops signs of a severe allergic reaction,
• has severe uncontrolled bleeding,
• has severe chest pain,
• becomes severely confused or unresponsive, or
• appears critically unwell.

Do not attempt to manage serious symptoms simply by drinking water or eating salt.

How to Measure Blood Pressure More Reliably at Home

If you monitor your blood pressure at home, technique matters.

Before taking a measurement:

• sit quietly and relax,
• support your back,
• keep your feet on the floor,
• support your arm,
• use the correct cuff size, and
• follow the instructions supplied with your validated blood-pressure monitor.

Keep a record if your healthcare professional has asked you to monitor your blood pressure.

A pattern of readings is generally more informative than becoming worried about one isolated measurement.

Low Blood Pressure vs High Blood Pressure

Low and high blood pressure should not be confused.

Low blood pressure (hypotension) generally refers to a reading below 90/60 mmHg.

High blood pressure (hypertension) means the pressure in the blood vessels remains higher than recommended.

High blood pressure is an important long-term cardiovascular risk factor.

Low blood pressure is different: many people have naturally low readings without experiencing health problems.

The important question with hypotension is often whether it is causing symptoms or has an underlying medical cause.

Related reading: Heart Attack vs Cardiac Arrest: Warning Signs, Prevention and What to Do

The Bottom Line

Low blood pressure, or hypotension, generally means a blood-pressure reading below 90/60 mmHg.

But a low number by itself does not necessarily mean something is wrong.

Some people naturally have low blood pressure and feel perfectly well.

Low blood pressure becomes more important when it causes symptoms such as dizziness, weakness, blurred vision, confusion or fainting, or when it results from an underlying medical condition.

Simple measures such as getting up slowly, maintaining appropriate hydration and avoiding sudden changes in posture can help some people.

However, persistent symptoms should be assessed by a healthcare professional so the underlying cause can be identified.

And sudden severe symptoms, collapse, major bleeding, severe allergic reactions or breathing difficulties require emergency medical attention.

Medical Disclaimer

This article is for general health information and does not provide individual medical diagnosis or treatment. Blood-pressure targets and treatment decisions depend on a person's medical history, medicines and other circumstances. Do not stop or change prescribed blood-pressure or heart medication without consulting an appropriate healthcare professional. Seek urgent medical assistance for severe or rapidly worsening symptoms.

Sources and Further Reading

NHS — Low blood pressure (hypotension)

https://www.nhs.uk/conditions/low-blood-pressure-hypotension/

British Heart Foundation — Low blood pressure

https://www.bhf.org.uk/informationsupport/risk-factors/high-blood-pressure/low-blood-pressure

NICE — Hypertension in adults: diagnosis and management

https://www.nice.org.uk/guidance/ng136

NICE — Recommendations, including postural hypotension

https://www.nice.org.uk/guidance/ng136/chapter/recommendations