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Thunderclap Headache: What It Means & Required Emergency Treatment

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Thunderclap headache symptoms include nausea, vomiting, loss of consciousness & weakness. Learn about the serious thunderclap headache causes and risk factors.

5 most common cause(s)

Subarachnoid Hemorrhage
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Transient Ischemic Attack
Carotid Artery Dissection
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Cerebral venous thrombosis
Illustration of a doctor beside a bedridden patient.
Viral encephalitis

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Symptoms of a thunderclap headache

A thunderclap headache is a sudden, severe headache that reaches maximal intensity within one minute of onset. A thunderclap headache differs from other headaches because of the speed with which it develops. While other severe headaches may require evaluation, a thunderclap headache is particularly worrisome as it is a common sign of an impending bleed in the brain. See a physician immediately for any thunderclap headaches. You will likely require imaging; once the cause of the headache is determined, your doctor will discuss treatments such as surgery, medications, and other interventions.

Common accompanying symptoms of a thunderclap headache

If you're experiencing a thunderclap headache, it's also likely to experience:

  • Nausea or vomiting
  • Loss of consciousness or altered consciousness
  • Facial drooping
  • Weakness
  • Neck stiffness or pain
  • High blood pressure
  • Seizures
  • Fever

Thunderclap headache causes and conditions

The most concerning and common cause of a thunderclap headache is an aneurysm rupture and subsequent bleeding in the brain. If you experience a headache that reaches maximal intensity within one minute of onset, see a physician immediately.


Bleeding in the brain may result in a thunderclap headache.

  • Aneurysm rupture: An aneurysm is a bulge that forms in a blood vessel in the brain due to a weakening in the wall. The area can rupture and cause bleeding in the brain. Most commonly, the vessel bleeds into the subarachnoid space, a compartment in between the brain and the skull. Aneurysms can also bleed into the brain tissue itself. Either of these scenarios can lead to severe thunderclap headache symptoms and can involve lost or altered consciousness.
  • Aneurysm warning headache: Sometimes, an aneurysm can cause a thunderclap headache days or weeks before it ruptures and bleeds. Almost half of people with bleeding into the subarachnoid space due to aneurysm rupture report a similar warning headache.

Vascular causes

Issues with arteries or smaller veins in the brain may cause a thunderclap headache.

  • Arteries in the brain: An ischemic stroke is when a clot forms or travels to an artery in the brain, blocking blood flow to the tissue. An ischemic stroke may present with a thunderclap headache, as well as neurologic symptoms such as slurred speech or weakness on one side of the body.
  • Veins in the brain: A blood clot can form in the veins in the head and present with a thunderclap headache, as well as neurologic symptoms such as problems with vision or weakness on one side of the body.
  • Arteries in the neck: The walls of the main artery in the neck can tear, leading to cervical artery dissection. This condition may present with a thunderclap headache as well as one-sided neck pain with or without neurologic symptoms such as blurry vision or facial drooping.
  • Arterial spasm: The narrow arteries in the brain can spasm, temporarily blocking blood flow to parts of the brain, and leading to thunderclap headache symptoms. Unlike other problems on the list, this block is reversible. It may be difficult to distinguish this thunderclap headache from one indicating a stroke or aneurysm rupture.

Other causes

Other causes of thunderclap headaches include the following.

  • Infection: Bacterial and viral infections in the brain are often associated with gradual headaches, but can sometimes resemble a thunderclap headache. Other symptoms of infection include fever and neck stiffness.
  • High blood pressure: Very high blood pressure can cause a variety of symptoms including headache, chest pain, blurry vision, or a change in mental status. The headache associated with high blood pressure is gradual, throbbing headache, but high blood pressure may also present with a thunderclap headache.

Viral encephalitis

Encephalitis is irritation and swelling (inflammation) of the brain, most often due to viral infections. Encephalitis caused by the herpes simplex virus is the leading cause. Several other causes of encephalitis (St. Louis, California, Japanese and Eastern Equine encephalitis infections) are transmitted by bites from an infected mosquito.

You should go to the ER immediately, where doctors can administer anti-infectious medications as soon as possible. If left untreated, this diagnosis is deadly.

Rarity: Rare

Top Symptoms: fatigue, being severely ill, loss of appetite, new headache, vomiting

Symptoms that always occur with viral encephalitis: being severely ill

Urgency: Hospital emergency room

Subarachnoid hemorrhage

Subarachnoid hemorrhage is bleeding in the area between the brain and the thin tissues that cover the brain. It's typically caused by a ruptured aneurysm (out-pouching of an artery's wall).

Call 911 immediately. This condition is a medical emergency requiring immediate attention.

Stroke or tia (transient ischemic attack)

Transient ischemic attack, or TIA, is sometimes called a "mini stroke" or a "warning stroke." Any stroke means that blood flow somewhere in the brain has been blocked by a clot.

Risk factors include smoking, obesity, and cardiovascular disease, though anyone can experience a TIA.

Symptoms are "transient," meaning they come and go within minutes because the clot dissolves or moves on its own. Stroke symptoms include weakness, numbness, and paralysis on one side of the face and/or body; slurred speech; abnormal vision; and sudden, severe headache.

A TIA does not cause permanent damage because it is over quickly. However, the patient must get treatment because a TIA is a warning that a more damaging stroke is likely to occur. Take the patient to the emergency room or call 9-1-1.

Diagnosis is made through patient history; physical examination; CT scan or MRI; and electrocardiogram.

Treatment includes anticoagulant medication to prevent further clots. Surgery to clear some of the arteries may also be recommended.

Rarity: Common

Top Symptoms: dizziness, leg numbness, arm numbness, new headache, stiff neck

Symptoms that never occur with stroke or tia (transient ischemic attack): bilateral weakness

Urgency: Emergency medical service

Cerebral venous thrombosis

Cerebral venous thrombosis (CVT,) or cerebral venous sinus thrombosis (CVST,) refers to a blood clot in certain veins of the brain.

There are two layers of material that form the lining between the skull and the brain. The occasional open spaces, or sinuses, between these two layers have veins running through them to drain blood and spinal fluid from the brain.

Cerebral venous thrombosis means that a blood clot (thrombosis) has formed somewhere within the veins of these sinuses.

This condition is caused by a congenital malformation in the brain; pregnancy; use of oral contraceptives; meningitis; use of steroids; and trauma to the head.

Symptoms include headache; nausea and vomiting; mental confusion; changes in vision; difficulty walking, moving or speaking; seizures; and coma. CVT is a life-threatening medical emergency. Take the patient to the emergency room or call 9-1-1.

Diagnosis is made through physical examination; CT scan or MRI; blood tests; and sometimes a lumbar puncture (spinal tap.)

Treatment includes anticoagulant medication to destroy the clot, followed by any rehabilitation that may be needed.

Rarity: Ultra rare

Top Symptoms: fatigue, headache, nausea or vomiting, loss of appetite, being severely ill

Symptoms that always occur with cerebral venous thrombosis: being severely ill

Urgency: Emergency medical service

Carotid artery dissection

A carotid artery dissection is the tearing of the walls of the carotid arteries, which deliver blood to the brain from the aorta. This is a medical emergency.

Call 911 immediately. Diagnosis is done by CT or MRI, and treatment involves anti-clotting medication for at least 3-6 months. Surgery may be necessary for those who can't get this medication.

Thunderclap headache treatments and relief

All thunderclap headaches require emergent medical evaluation. There are no appropriate ways to treat a thunderclap headache at home.

Medical treatments

The following may occur when consulting your physician.

  • Imaging: There are multiple ways to obtain images of the brain, including CT scan, MRI, or MR angiography, which looks specifically at the blood vessels in the brain.
  • Spinal tap: In some cases, bleeding in the brain may not appear on imaging. Your doctor may then order a spinal tap to look for signs of bleeding or to look for a brain infection.
  • Surgery: In some instances, aneurysms require surgical intervention.
  • Endovascular intervention: Some aneurysms are repaired by inserting a small metal coil into the blood vessel to prevent bursting. Some strokes are reversed by removing the clot from the blocked blood vessel. These procedures are known as endovascular interventions because they treat the problem by going inside the blood vessel. Your doctor will discuss the risks and benefits of these procedures, if necessary.
  • Medications: If an infection or high blood pressure are causing your headache, your doctor may prescribe antibiotics or blood pressure medications. If a stroke is the cause of the headache, a doctor may prescribe blood thinners.
  • Pain medication: You and your care team should determine the cause of your thunderclap headache and not simply treat the pain. However, once the cause is determined, your doctor may prescribe pain medication to help relieve headache symptoms.

FAQs about thunderclap headache

How long do thunderclap headaches last?

A thunderclap headache does not last a specific amount of time. It will reach maximal intensity within one minute of onset and is very severe. A thunderclap headache is a dangerous symptom. If you suspect you are having a thunderclap headache, go to the nearest emergency department.

Why am I nauseous when I have a thunderclap headache?

A thunderclap headache can have multiple causes. The classical explanation is an aneurysm, a dilated arterial blood vessel, that is at risk of bursting within the brain. Many of the other causes, however, are just as dangerous and warrant immediate care. Nausea is a common symptom of increased pressure within the brain.

Are thunderclap headaches a warning sign of a brain aneurysm?

Yes. They are classically known as "sentinel headaches," or headaches that predict the presence of an unruptured aneurysm within the brain. This condition is a medical emergency and treatment should begin as soon as possible.

What are the differences between a thunderclap headache and a migraine?

A thunderclap headache reaches maximal intensity within one minute and may affect both sides of the head. A migraine is usually one-sided, gradual in onset, and may involve changes in vision. A thunderclap headache may disappear quickly or not at all. Silence and darkness can soothe migraines. Most people with migraines have had them before and can recognize them readily.

What does a thunderclap headache feel like?

A thunderclap headache is often referred to as "the worst headache I've ever had in my life," as it is intense and extremely rapid in onset. This headache can be immediately debilitating, constant, or it can decrease in intensity. If it does decrease in intensity or disappear, you should still seek immediate medical care.

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The stories shared below are not written by Buoy employees. Buoy does not endorse any of the information in these stories. Whenever you have questions or concerns about a medical condition, you should always contact your doctor or a healthcare provider.
Dr. Rothschild has been a faculty member at Brigham and Women’s Hospital where he is an Associate Professor of Medicine at Harvard Medical School. He currently practices as a hospitalist at Newton Wellesley Hospital. In 1978, Dr. Rothschild received his MD at the Medical College of Wisconsin and trained in internal medicine followed by a fellowship in critical care medicine. He also received an MP...
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