Cluster headache refers to the characteristic grouping or clustering of attacks. Cluster headaches may also be known as histamine headache, red migraine, Horton’s headache, and cephalalgia or sphenopalatine neuralgia. The headache periods can last several weeks or months, and then disappear completely for months or years leaving considerable amounts of pain-free intervals between series. Cluster is one of the least common types of headache, and the cause is unknown. Cluster headaches occur more often in men than women. The pain is vascular in nature, and caused by blood vessel swelling in the head. The autonomic nervous system is intimately involved in the genesis of cluster headache and it appears to be mediated by alterations in the hypothalamic area. This area and adjacent areas are believed to regulate both daily as well as yearly cycles that go on in the body. Although it is rare, it is possible for someone with cluster headache to also suffer from migraine headache. Cluster headache starts suddenly, and a minimal warning of the oncoming headache may occur, including a feeling of discomfort or a mild one-sided burning sensation. This pain is of short duration, generally 30 to 45 minutes. However, the headache itself may last anywhere from a few minutes to several hours and will disappear only to recur later that day. Most sufferers get one to four headaches per day during a cluster period. They occur regularly, generally at the same time each day. Cluster headaches often awaken the sufferer in the early morning or during the night and have been called "alarm clock headaches."

Lithium is a naturally occurring salt that was first used for treating certain psychiatric problems. Several headache specialists recognized that it could be useful in treating cluster headaches as well. This medication acts in the brain to re-regulate hypothalamic and other brain areas related to cluster and some other headaches. It is most useful in cluster headache. Here it is used primarily to treat those who have chronic cluster headache. It may be useful in episodic cluster headache.