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Overview - Subarachnoid haemorrhage

A subarachnoid haemorrhage is an uncommon type of stroke caused by bleeding on the surface of the brain. It's a very serious condition and can be fatal.

Symptoms of a subarachnoid haemorrhage

There are usually no warning signs, but a subarachnoid haemorrhage sometimes happens during physical effort or straining, such as coughing, going to the toilet, lifting something heavy or having sex.

The main symptoms of a subarachnoid haemorrhage include:

  • a sudden severe headache unlike anything you’ve experienced before
  • a stiff neck
  • feeling and being sick
  • sensitivity to light (photophobia)
  • blurred or double vision
  • stroke-like symptoms – such as slurred speech and weakness on one side of the body
  • loss of consciousness or convulsions (uncontrollable shaking)

A subarachnoid haemorrhage is a medical emergency. Dial 999 immediately and ask for an ambulance if you or someone in your care has these symptoms.

How a subarachnoid haemorrhage is treated

A person with a suspected subarachnoid haemorrhage needs a CT scan in hospital to check for signs of bleeding around the brain.

If a diagnosis of subarachnoid haemorrhage is confirmed or strongly suspected, you're likely to be transferred to a specialist neurosciences unit.

Medicine will usually be given to help prevent short-term complications, and a procedure to repair the source of the bleeding may be carried out.

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Causes of subarachnoid haemorrhages

Subarachnoid haemorrhages are often caused by a burst blood vessel in the brain (a ruptured brain aneurysm).

It's not known exactly why brain aneurysms develop in some people.

But certain risk factors have been identified, including:

Severe head injuries can cause subarachnoid bleeding, but this is a separate problem known as a traumatic subarachnoid haemorrhage.

Read more about the causes of subarachnoid haemorrhages.

Who's affected?

Subarachnoid haemorrhages can happen at any age, but are most common in people aged between 45 and 70. Slightly more women are affected than men.

Subarachnoid haemorrhages are also more common in black people compared to other ethnic groups. This could be because black people are more likely to have high blood pressure.

Reducing your risk

There are some things you can do to reduce your risk of a subarachnoid haemorrhage.

The most effective steps you can take to reduce your chances of having a subarachnoid haemorrhage are:

  • stop smoking – your GP can refer you to an NHS Stop Smoking Service for help and advice, or you can call the NHS Smoking Helpline on 0300 123 1044
  • moderate your alcohol units (alcohol consumption)
  • take steps to prevent high blood pressure – such as regular exercise, eating a healthy diet and losing weight if you're overweight

Possible complications

A subarachnoid haemorrhage can cause both short and long-term complications.

Serious short-term complications can include further bleeding at the site of any aneurysm and brain damage caused by a reduction in blood supply to the brain.

Long-term complications include:

  • epilepsy – where a person has repeated seizures (fits)
  • problems with certain mental functions, such as memory, planning and concentration
  • changes in mood, such as depression

Read more about the complications of a subarachnoid haemorrhage.


Although the outlook for subarachnoid haemorrhage has improved in the last few decades, it can be fatal, and people who survive can be left with long-term problems.

Recovering after a subarachnoid haemorrhage can also be a slow and frustrating process, and it's common to have problems such as:

  • extreme tiredness
  • headaches
  • problems sleeping

Read more about recovering from a subarachnoid haemorrhage.


Social care and support guide

The social care and support guide explains your options and where you can get support if:

  • you need help with day-to-day living because of illness or disability
  • you care for someone regularly because they're ill, elderly or disabled – including family members

Page last reviewed: 02 December 2021
Next review due: 02 December 2024