Analgesic overuse is not a cause of chronic daily headache

Large-scale, population-based studies indicate the majority of patients with CDH do not overuse analgesics. These studies support similar observations in populations where analgesics are used infrequently (India) and long-term studies that indicate the persistence of CDH in patients who have been withdrawn from analgesics and treated aggressively with pharmacologic and biobehavioral treatment. Emerging experimental evidence suggests that in some patients, CDH may represent a chronic, relapsing, progressive disorder associated with structural and physiologic changes within the brain resulting in chronic and continuous pain. The identification of those patients with episodic migraine (and other primary headaches) who are at risk for developing daily headache is a clear priority, and a better understanding of the underlying biology of this disorder will hopefully identify new molecular targets for drug development and facilitate our ability to manage these patients more effectively. However, there is abundant clinical evidence that supports the assertion that the frequent or continuous use of immediate-relief medications can maintain, exacerbate, and in some patients, even induce a pattern of daily headache. There is also a robust body of experimental evidence to support the concept of analgesic-induced abnormal pain when these drugs are administered continuously, likely due to physiologic and plastic changes in nociceptive networks. In this regard, there is converging evidence from the chronic pain and headache literature, and advances in the headache field should be facilitated by closer collaboration between these two groups of investigators. Certainly, the prolonged use of large amounts of analgesic medication may lead to tolerance, habituation, dependence, and is a significant cause of morbidity related to renal, gastrointestinal, and hepatic toxicity. The recommendation that elimination of analgesic overuse remain a priority in these patients is sound medical advice. A proportion of patients will improve and the overall headache-associated disability may decrease even if headaches remain daily or near daily in frequency. The viewpoints regarding the causal relationship between analgesics and CDH are certainly not mutually exclusive. Causality appears to be bi-directional and the two phenomena (daily headache and analgesic-induced headache) may coexist. However, the reflex diagnosis of "rebound" or "medication-induced" headache (a retrospective diagnosis) in such patients is misguided, and the notion that simple discontinuation of analgesics will result in the restoration of an episodic pattern of headache in the majority of patients appears incorrect. A significant proportion (perhaps the majority) of these patients continue to suffer significant long-term headache-related disability, and the careful study of chronic migraine is, therefore, a major priority over the next decade.