Chronic migraine is a disorder in which a person experiences migraines 15 or more days each month. The cause of chronic migraine isn't clear. Some research suggests that it may be due to changes in parts of the brain that control pain. Chronic migraine is not due to overuse of pain medications.

Treatment of chronic migraine may include certain antidepressants, anti-seizure medications or cardiovascular drugs. However, even with such treatment, migraines may persist.

Sometimes, episodic migraines increase in frequency to daily or near-daily migraines — often without the usual features of a migraine, such as nausea or light sensitivity. In such cases, these migraines are referred to as transformed, or evolved, migraines.