Cluster headaches (CHs)

What are cluster headaches (CHs)?

Cluster headaches (CHs) are a relatively uncommon headache disorder. This kind of headache affects people in bouts (clusters), over periods of weeks or months. According to the World Health Organization, CHs affect around one in a thousand people. They primarily affect adults, and the first episodes usually begin to appear during a person’s 20s or thereafter.

The most notable characteristic of CHs is the unprecedented intensity of the pain which those affected experience during a headache attack. Cluster headaches are described as one of the most painful types of headache. The exact causes of cluster headaches are unknown, but they are six times more likely to affect men than women.[1] Currently identified possible triggers include stress, exposure to allergens and heavy alcohol use.

An affected person may experience bouts (clusters) of 1-8 headaches per day, also known as cluster periods, for intermittent periods of time lasting weeks or months, usually followed by remission periods when the headaches stop. During remission, no headaches occur for months and sometimes even years. The cycles might be in step with the changing of the seasons. However, some chronic,year-round, presentations of the condition do not seem to have any connections to seasonal or environmental triggers.[2]

Although CHs are incredibly painful, they are not life-threatening, and treatment can reduce the frequency and severity of the headaches. In the short-term, treatment for cluster headaches focuses on lessening the symptoms of the headache attack. This usually involves specialized painkillers and/or oxygen therapy, i.e.inhaling pure oxygen through a face mask. Long-term treatment of CHs focuses on lifestyle changes and prevention.

Symptoms

CHs are a subtype of headache called a trigeminal autonomic cephalalgia (TAC). Headaches of this kind are unilateral, meaning that they affect one side of the head and face:[3]

  • Cephalalgia is the medical term for a dull, persistent, and usually moderately intense, pain in the head region.
  • The word trigeminal refers to the trigeminal nerve, responsible for sensation in the face and motor functions such as biting and chewing. Correspondingly, the area affected by CHs is the facial area and the eye area in particular. CHs can affect either the left or the right side of the head, but most people find that they are usually affected on the same side each time.
  • The symptoms of CHs are described as autonomic processes because the body performs them automatically, e.g. a runny nose and teary eyes.

The pain associated with a cluster headache develops very suddenly and is incredibly intense. It has been described as an unbearable, piercing, burning and excruciating sensation.[2]

The intensity of the pain may cause people to move in an agitated manner during an attack. It is common for people to pace up and down during a headache attack, and some people even report making desperate attempts to bang their heads on walls and objects in response to the intensity of the pain.

In addition to its characteristic pain, one or more the following symptoms may be present during a CH:[2][4]

On the side of the head affected:

  • A reddened, teary eye
  • Shrinking of the pupil in the eye
  • A drooping or swollen eyelid
  • A blocked and/or stuffy nostril

Other symptoms include:

  • A sweaty face and forehead
  • A pale or flushed face
  • Restlessness (pacing and agitated movement)
  • Spreading of the pain to the face, head, neck and shoulders
  • A need to avoid light and sound

Many people only experience one or two of these symptoms in addition to the painful sensation, and it is possible for a person’s symptoms to vary between attacks. However, most people’s symptoms only vary very slightly from one headache attack to another.[5]

Good to know: A cluster headache is also known as a migrainous neuralgia, but is a different kind of headache from a migraine. Migraines are often confused with cluster headaches due to the fact that they can also be very painful and can affect people frequently or in bouts for periods of time, so it is important to be aware of their different characteristics to ensure that a person affected by headaches receives treatment for the appropriate type. See the “Cluster headache FAQs section below and this resource on migraines for more information.

Duration and frequency

The natural duration of a cluster headache is usually approximately between 15 minutes and three hours, if there is no specialized treatment to reduce its pain and duration. CHs usually occur one to eight times per day, at the same time or times. It is most common for CHs to occur at night, one to two hours after falling asleep, waking up the affected person.[6]

After the headache, the pain usually alleviates very suddenly, leaving the affected person pain-free, and, usually, physically tired.

Episodic cluster headaches

In people with episodic cluster headaches, CHs will occur every day for periods of weeks or months; six to twelve weeks is normal. This is the case in around 80 percent of people affected by CHs.[7]

The rest of the time, a person affected by episodic CHs will experience periods of remission with no CHs. These periods of remission may last months or even years before the next cycle of headaches occurs. Periods in which CHs occur, will usually happen at the same time or times each year. Many affected people experience CHs during Spring and Fall.

Chronic cluster headaches

For 20 percent of people affected by CHs, the condition is chronic, meaning that the headaches occur all year round rather than in periodic or seasonal cycles. CHs are considered chronic if a bout of CHs lasts for more than a year and/or if periods of remission typically last for less than one month.[7]

Causes

Only a small amount of information about the physiological mechanism that leads to cluster headaches is known:

  • CHs are linked to increased activity in a part of the brain called the hypothalamus, which contains a control centre for many of the functions of the autonomic nervous system. A greater intensity in the activity of the hypothalamus during CH attacks has been detected by brain imaging studies on people affected by CHs.[8] However, the exact relationship between CHs and the activity of the hypothalamus is not yet understood.
  • CHs are also been linked to a person having elevated levels of histamine,a chemical produced as part of the body’s immune response to allergens. According to historical research into cluster headaches, people affected by CHs are likely to develop a headache attack when histamine is medically administered.[9]
  • A person’s food intake may contain histamine-rich foods, which can cause CHs. Histamine levels in foods vary, depending on how processed, ripe or matured they are. Foods which are rich in histamine and may cause CHs include: salty foods such as crisps and cured meats, alcohol, vinegar, cocoa and chocolate, shellfish, beans and pulses, and matured cheeses. Keeping a food diary may help to identify foods which are causing CH bouts or attacks.
  • Elevated levels of serotonin, a neurotransmitter; mainly produced in the brain, and found in the nervous system and gut which promotes feelings of well-being, has also been linked to CHs.

However, the relationships between having elevated levels of histamine and/or serotonin and the development of CHs are also unknown.

Good to know: Selective serotonin reuptake inhibitors (SSRIs) ‒ medications which are used to treat a variety of mental health conditions including depression and anxiety ‒ are not believed to cause cluster headaches, despite the fact that they increase the level of serotonin in the brain. This is primarily because they are prescribed to raise serotonin levels which are believed to be low.

However, it is important that people who are using SSRIs inform their doctor when seeking treatment for CHs: SSRIs have cross-reactivity with certain medications used to treat CHs. For example, the first-line treatment for CHs, sumatriptan, from the triptan class of medications, works by stimulating serotonin receptors in the brain. The stimulation of the serotonin receptors resulting from the use of triptans has an effect called negative feedback regulation on the brain’s 5-HT synthesis. This effect leads to a larger than normal amount of serotonin being available for use by the brain.

Due to this effect, triptans may cause serotonin syndrome when used in conjunction with SSRIs. Serotonin syndrome is a condition involving high body temperature, sweating and tremors, occurring as a result of too much serotonin in the body.

Triggers

In people who are affected by cluster headaches, certain triggers have been identified which may bring on a bout of cluster headaches. These factors have also been found to trigger headache attacks during a period when a person is experiencing a bout of CHs.

Known triggers of CHs in people already affected by the condition include:[4][10][11]

  • Seasonal changes - CHs are believed to be linked to circadian rhythmicity and are therefore likely to occur as the body adjusts to taking in more or less light during the day: a property of the shoulder seasons rather than the extreme ones.
  • Weather changes
  • Exertion
  • Drinking alcohol
  • Smoking tobacco
  • Stress
  • Exposure to allergens, such as pollen and pet dander
  • Strong smells, such as paint, petrol or perfume
  • Temperature changes - hot towels, hot showers
  • High altitudes - air travel, trekking
  • Nitroglycerin, a chemical compound which is used in some medications for chest pain
  • Foods high in nitrates, e.g. preserved meats
  • Elevated levels of histamine
  • Elevated levels of serotonin
  • Cocaine

Risk factors for developing cluster headaches

The exact cause of cluster headaches is unknown, but certain factors render a person at increased risk of developing cluster headaches. These include:[10]

  • Being male
  • Using tobacco products; however, quitting using tobacco products is not known to affect a person’s chances of developing the condition
  • Drinking alcohol
  • Being older than 20
  • Previous trauma or surgery to the head
  • A family history of cluster headaches (research investigating CHs in various population groups has reliably identified that a small proportion ‒ up to 20% ‒ of participants have relatives who are also affected).

A significant proportion of people who develop cluster headaches use tobacco products and/or consume alcohol heavily.[10]

Risks associated with cluster headaches

Although a person may worry that they are dying during a cluster headache due to the intensity of the pain, this condition is not life-threatening and does not pose any direct health risks. However, relative to the general population, people affected by CHs may be more prone to certain behaviors which carry severe health risks, including:[10]

  • Injuring themselves during CH attacks
  • Alcohol abuse
  • Other forms of substance abuse
  • Suicide attempts, in particular in cases of severe and persistent CHs)

Diagnosing and beginning treatment for CHs is the best means of minimising these risks.

For people who have been correctly diagnosed with this condition, and who are being treated effectively, the most likely negative impact of CHs is a reduced quality of life, due to having to spend time away from work, education or social events during headache attacks. The extent to which a person’s quality of life is reduced by CHs can, in many cases, be lessened by accessing effective treatment options.

Diagnosis

Anybody who thinks they may have experienced a cluster headache should seek medical attention without waiting for a repeat occurrence. To reduce the potential severity and overall impact of CHs on a person’s quality of life, it is important to diagnose and begin treating the condition as soon as possible.

There are no specialized diagnostic tests to establish whether a person is affected by cluster headaches. To diagnose CHs, a doctor will assess the following criteria:

  • Brain function: In order to rule out any neurological problems, such as brain or vessel abnormalities, which may be the cause of the headache(s), a brain scan will be performed. If any previously-unknown abnormalities are revealed, these will be considered to be the cause of the headaches, and a diagnosis of CHs will not be given at this time. Instead, the abnormalities will be investigated further and treated.
    In otherwise-healthy people affected by CHs, the brain scan will be normal with no abnormalities. Doctors can then be confident that the CH attacks are caused by CH disorder rather than any impairment of brain function.
  • A person’s medical history, with a focus on whether the person’s symptoms could relate to any other headache disorders.
  • Whether a person has a family history of cluster headaches. Although the link between genetics and CHs is not understood, people with relatives affected by CHs are more likely to develop the condition.
  • Whether a person’s experience of their headache(s) matches the diagnostic criteria for a cluster headache, which include having at least one symptom which is ipsilateral (on the same side of the head as the pain) in the eye, nose or face, restlessness or agitation, a duration of 15 minutes to three hours without effective response to medication or painkillers, a frequency of between one attack every other day or eight attacks per day and an incredibly severe pain.

Avoiding misdiagnosis

Doctors will be aware that a person may be affected by other primary headache disorders, which may result in them experiencing headaches that are similar to cluster headaches. These include:[3][12][13]

  • Trigeminal neuralgia: A chronic pain disorder affecting the same nerve that is involved in cluster headaches.
  • Migraine: Some headache attacks can feature autonomic features such as teary eyes. Migraines can also often occur in bouts, which leads to the widespread misconception that a person is experiencing cluster headaches, when they are in fact experiencing clusters of migraines.
  • Hemicrania continua: A chronic, persistent headache that usually occurs on the same side of the face and head, usually consisting of a constant dull pain which intermittently becomes piercing.
  • Short-lasting, unilateral, neuralgiform headache attacks with conjunctival injection and tearing (SUNCT): Like CHs, SUNCT headaches are a subtype of trigeminal autonomic cephalalgia headaches, but their duration is much shorter than cluster headaches.

Treatment

People who have been diagnosed with CHs are usually treated by a type of doctors specialising in brain and nerve conditions called a neurologist. Those affected by CHs will require both short and long-term treatment in order to manage their headache disorder:

  • Short-term treatment for CHs focuses on reducing the pain and duration of the headache attack.
  • Long-term treatment of CHs aims to reduce the frequency of headache attacks and to prolong the periods of remission between bouts. With effective treatment, a person affected by chronic CHs may be able to reduce the frequency of their headaches to the point at which their CH disorder becomes episodic.

Short-term treatment: managing a cluster headache attack

After having diagnosed CHs, doctors will discuss a range of treatments which a person can use during a headache attack in order to relieve their pain. The pain associated with a CH is so severe that it cannot be alleviated with traditional over-the-counter (OTC) painkillers.

Specialized treatments for CHs can usually relieve headache pain in 15-30 minutes. These treatments are called abortive agents because they begin to relieve (abort) pain more quickly than OTC painkillers, which are designed to be swallowed. They can be administered by vaporisation, i.e. breathing them in through the nose, or by injection into a muscle, or vein.[14]

The principal abortive agents used to relieve the symptoms of a CH attack are oxygen therapy and sumatriptan injections.

Oxygen therapy

This treatment involves breathing in pure oxygen through a mask at the start of a CH attack. Masks and containers of pure oxygen will be provided by a person’s doctor, and they will be shown how to use the equipment so that they can carry out this treatment themselves, independently, whenever a CH strikes.

The rate at which the oxygen is dispensed from the container can be adjusted, and people are usually recommended to breathe in oxygen at a rate of around 15 litres per minute at the start of the attack, which they can decrease to a rate of six to eight litres per minute when the symptoms subside. It is important to continue breathing in the oxygen for five to ten minutes after the attack has finished, otherwise it may return.

Sumatriptan (triptan class medication) injections

Sumatriptan is a medication which is used in the treatment of migraines and cluster headaches. It works by narrowing the blood vessels in the brain, which stops the transmission of pain signals. Sumatriptan works best as an abortive agent when injected into the skin and can be injected into the outside of the thigh or upper arm. Never inject sumatriptan into a vein or muscle.[15]

A person’s doctor will demonstrate how to inject sumatriptan, and these injections are then safe to use independently, ideally at the first sign of a CH attack. Sumatriptan is most effective when used at the start of a CH attack. Doctors will recommend the appropriate dose and dosing schedule in each case.[16]

It is also possible to use sumatriptan as a nasal spray, but this method of administration is considered to be significantly less effective at reducing CH symptoms than sumatriptan injections.

Always inform a doctor if a person is on a course of selective serotonin reuptake inhibitors (SSRIs) medication before taking sumatriptan. SSRIs increase the levels of serotonin in the brain, a property which sumatriptan shares. Using two serotonergic medications, agents which increase serotonin levels, simultaneously can lead to serotonin syndrome: an adverse reaction to having too much serotonin in the body.

Recovery after a CH attack

CH attacks can be physically exhausting. Although the pain of a cluster headache will alleviate after using an abortive agent, the affected person is likely to benefit from a period of recovery, which may involve resting, spending time in a calm, quiet room and drinking water to stay hydrated.

If a person is likely to be affected by CH attacks at work, it is recommended that they inform their workplace, so that their employers understand the nature of the condition and can accommodate their needs. During a bout of CHs, these may include working from home or taking several breaks to manage attacks.[17]

Long-term treatment for cluster headaches

For people who experience cluster headaches so frequently that they cannot manage the condition effectively using oxygen therapy or sumatriptan injections, additional treatments may be recommended. These include:[18][19]

  • Transcutaneous vagus nerve stimulation (TVNS): This treatment involves providing the affected person with a small, handheld device which they can use to treat CH attacks when they occur. The device can also be used in between attacks to reduce their frequency. The TVNS device works by emitting a low-voltage electrical current, which, when applied to the skin on the neck near the vagus nerve, will stimulate it, relieving tension and pain. However, TVNS can, in rare cases, cause a CH attack to develop, and this treatment option may therefore be unsuitable for some people.[20]
  • Sphenopalatine ganglion (SPG) stimulation: The sphenopalatine ganglion is a nerve bundle which is located behind the nose. In people affected by CHs, low-voltage electrical stimulation of of the SPG can relieve the pain of a CH attack. SPG stimulation requires the implantation of a device – which is smaller than an almond – into the side of the face.[21]

General anaesthetic is used to implant the device, and a small incision is made in the upper gum on the side most affected by CHs. The implantation procedure takes around an hour, and there is no visible scarring. After implantation, people affected by CHs can activate the device to stimulate the SPG by using a handheld monitor when they feel an attack coming on. The SPG can also be stimulated between attacks to reduce their frequency.

Prevention

The causes of cluster headaches are unknown, so it is not possible to prevent the development of the CHs disorder itself. However, smoking tobacco is a known cause of CHs, and giving up smoking may therefore reduce a person’s chances of developing them.

People who are affected by CHs can take measures to prevent headache attacks, including avoiding triggers and making healthy lifestyle choices.

Being aware of triggers

Keeping a diary of the circumstances surrounding one’s CHs can help a person to identify any possible triggers of headache attacks within a bout of CHs. Logging one’s CHs can also potentially help to establish the overall triggers of CH bouts, such as seasonal changes.

The affected person can then make lifestyle choices aimed at avoiding triggers, e.g. not wearing perfume in Spring and Fall, if their bouts of CHs generally occur during seasonal changes and strong smells are found to be a likely triggering factor.

Good to know: Many known triggers of CHs only cause a person to develop a headache if they are experiencing a bout. During a period of remission, a person may be able to encounter these triggers – such a drinking alcohol in moderation or smelling a strong scent – without being struck by a CH.

Preventative medications

Preventative medications for CHs vary in effectiveness between people, and a person may need to try several different forms of medication to find the one that is right for them. A person may take preventative medication all year round in the case of chronic cluster headaches, or periodically to prevent headache attacks during a bout.[2]

The first-line medication for preventing CHs is a type of medication regularly used in the treatment of high blood pressure, called a calcium channel blocker. In this case, it works to reduce vasoconstriction, which helps prevent CH attacks. These kinds of medications may cause heart problems to develop in some people, so a person’s heart will be monitored regularly, using an ECG machine when they are using this medication, to safeguard against this.[22]

Other medications which may be prescribed to as preventative treatments for CHs include:[22][23]

  • Corticosteroids: These medications are usually used in bursts of 2-3 weeks, generally to help break a cycle of CHs or in conjunction with other therapies that take longer to take effect. Due to the side-effects associated with long-term use, such as high blood sugar and the thinning of bones, these medications are suitable for short-term use only.
  • Greater optical nerve block: This treatment involves injecting an anaesthetic and steroid medication into the nerves that supply the scalp, at the back of the head. It is carried out in hospital by a doctor and can bring about periods of remission in people with CH disorder lasting a month or more. The procedure takes around a minute to perform and can be repeated every two months.
  • Lithium carbonate: Most often prescribed to treat chronic cluster headaches, this oral medication can help to re-regulate hormonal imbalances within the brain, reducing the frequency of CH attacks. However, use of this medication must be accompanied by regular blood tests to measure the levels of lithium in the blood. Having elevated levels of lithium for prolonged periods can cause problems such as kidney damage. Problems such as this can be avoided with close medical supervision.[24]
  • Anticonvulsant medication: These kinds of medication have been found to be effective in inducing periods of remission in people affected by CHs and in reducing the frequency of attacks when taken long-term. It is taken orally, and the dosage is usually increased over time at the discretion of a person’s doctor.[25]

Doctors will help to decide on the preventative medication(s) that are most suitable for each person, according to their pattern of CH bouts and general health.

Making healthy lifestyle choices

Although medical treatments are usually needed in order to bring cluster headache disorder under control, many people who are affected by CHs find that making certain changes to their lifestyle can help them in managing the condition and can reduce the frequency of headache attacks. These include:

  • Relaxation: Practicing relaxation skills such as yoga and deep breathing can help to diffuse stress and aid muscle relaxation. Setting aside periods of the day for relaxation and taking regular breaks from activities which involve sitting or standing in the same position can help to diffuse the buildups of muscle and nerve tension that contribute to CHs.
  • Resting well: Getting eight hours of sleep a night and going to bed at the same time each day can help to reduce stress, which can reduce the frequency of CHs.
  • Exercising regularly: Exercise releases beta-endorphins in the body, which can relieve stress. Exercising for 20 minutes, three times per week, can help to decrease the frequency of CHs and the severity of individual attacks.
  • Staying hydrated: Drinking eight glasses of water or other non-alcoholic, non-caffeinated beverages per day can help. For people who are affected by chronic or persistent CHs, opting for non-alcoholic beverages instead of drinks containing alcohol all year round can help to prevent CHs. Cutting down on, or cutting out, caffeine, can also help prevent CHs.
  • Seeking help to quit using tobacco products: The likelihood of being affected by CHs is greater among people who consume tobacco products than those who do not. In people with CHs, quitting is recommended. Doctors will be able to provide a range of resources on quitting smoking and connect a person to support programmes suited to their needs.

Cluster headaches FAQs

Q: What are the key differences between a cluster headache and a migraine?
A: Cluster headaches are unilateral (affecting one side of the head). This is one of the principal factors which distinguish CHs from migraines. Migraines involve a more generalized pain and typically affect both sides of the head at once. Additionally, the duration of a migraine is usually much longer than that of a CH, up to 72 hours.[26] People affected by a migraine tend to want to sit or lie down, whereas a person experiencing a CH is prone to agitated movement. See this resource on migraine headaches for more information.

Q: Are any home remedies or natural products effective at treating CHs?
A: The two most popular natural remedies for cluster headaches are:

  • Melatonin: Taking supplements of melatonin, a hormone found naturally in the body which helps regulate sleep cycles, has been found to help reduce the frequency of cluster headache attacks.[27]
  • Capsaicin: Using a nasal spray or cream containing capsaicin, a compound with anti-inflammatory properties, found in hot peppers, has been found to help reduce the frequency of cluster headache attacks.[28]

Not much clinical research has been carried out to establish the efficacy of either treatment in comparison to conventional treatments for cluster headache relief, such as suboptical steroid injections. In the evidence-based guidelines on treatments for cluster headaches devised by the American Headache Society, melatonin supplements are rated at grade C, i.e. possibly, rather than probably or certainly, helpful as a treatment for CHs, and intranasally applied capsaicin is rated at grade U, meaning that there is insufficient evidence to make a recommendation.[29]

If a person wishes to incorporate natural remedies such as these into their treatment plan for CHs, they should consult a doctor before choosing products or beginning to use them. These treatments may not be suitable for everyone. Furthermore, some natural products may contain ingredients which do not combine safely with other treatments or medications.


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