What causes low blood pressure and what are the symptoms? (2024)

We explain what leads to low blood pressure and how it’s measured and treated.

Many people will have heard of high blood pressure(hypertension), which is a major medical concern. If it’s not treated, high blood pressure can lead to heart attacks, strokes, kidney damage and even premature death.

Whereas low blood pressure(hypotension) is less talked about.

This is because it’s considered less dangerous to our health.

But if your blood pressure is too low it can cause health problems and may be a sign you have an underlying health condition.

What is low blood pressure (hypotension)?

Blood pressure is the pressure of the blood in your arteries - the vessels that carry blood from your heart to your brain and the rest of your body.

You need a certain amount of pressure to get this blood around your body.

When your blood pressure drops, your heart rate increases and blood vessels in other parts of your body constrict (narrow) to help maintain blood pressure.

If your heart rate does not increase enough, or your blood vessels do not constrict enough, your blood pressure will fall.

How is low blood pressure measured?

To find out if you have low blood pressure, a healthcare professional will measure it.

This is usually done with a cuff that squeezes your upper arm. The machine then gives you a reading of two numbers in millimetres of mercury (mmHg).

The first, higher number, is your blood pressure when your heart is pushing blood around your body. The second is the pressure in between heart beats.

The NHS has a general guide that can tell you if your reading is within the normal range:

• Low blood pressure: under 89/59mmHg
• Normal blood pressure: between 90/60 mmHg and 120/80 mmHg
• High-normal blood pressure: between 120/80 mmHg and 140/90 mmHg - you may be at risk of high blood pressure in the future.
• High blood pressure: 135/85 mmHg or above if your reading was taken at home, or 140/90 mmHg or above if your reading was taken at a clinic, GP surgery or pharmacy.

If you’re over 80, ideally blood pressure should be under 150/90 mmHg (or 145/85 mmHg if it is taken at home). This is a slightly higher because your arteries become stiffer as you age.

What are the symptoms of low blood pressure?

Most people with low blood pressure do not notice any symptoms.

However, in some cases it can cause:

• light-headedness or dizziness
• fainting
• blurred vision
• weakness
• difficulties in concentration or confusion
• nausea (feeling sick)

What causes low blood pressure?

You may find that your blood pressure drops when you:

• Stand up from sitting or lying down – this is a sign of a type of low blood pressure called postural hypotension (also known as orthostatic hypotension). Medicines for Parkinson's disease and erectile disfunction can increase the risk of this.
• Eat - as more blood flows to your digestive system afterwards.

Low blood pressure can also be caused by:

• Side effects from some medicines: such as medicines for high blood pressure, heart disease or depression, as well as some over-the-counter and herbal products.
• Medical conditions: these include heart failureor arrhythmia(abnormal heart rhythm), diabetes, thyroid problems and Parkinson’s disease.
• Blood loss: being dehydrated, donating blood or severe injuries can lead to a drop in blood volume and therefore lower blood pressure.
• Medical emergencies: septic shock(when bacteria from an infection enters the blood stream) and anaphylactic shock (severe allergic reaction) can cause dangerously low blood pressure.
• Pregnancy: low blood pressure is fairly common in pregnancy, and not usually a cause for concern.

Treatments for low blood pressure

Making simple lifestyle changes can be an effective way to improve low blood pressure.

This includes:

• drinking more fluids - check with your doctor first if you are on a daily fluid restriction
• raising your legs
• wearing support stockings – these can improve circulation and increase blood pressure, but make sure to ask your doctor if this is suitable for you
• changing or altering the dose of medicine you are taking if approved by your doctor

But if low blood pressure is becoming a problem for you, speak to your GP.

They may be able to work out and treat the underlying cause of your low blood pressure.

Low blood pressure can also be treated with certain medicines, depending on what’s causing it, such as:

1. Beta-agonists or alpha-agonists: beta-agonists make the heart beat faster, while alpha-agonists narrow the blood vessels.
2. Fludrocortisone: this is a steroid that makes your kidneys retain water and salt, increasing your blood volume.

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Updated 30 July 2024