The concept that headache treatment per se may be the cause of chronification of headache is not new,3 but our understanding of this concept, and the terminology defining it, have changed throughout the years. The criteria for MOH are based on expert consensus rather than formal evidence. According to the current definition in the latest (2013) International Classification of Headache Disorders–3 beta, MOH is essentially defined as headache on 15 days or more per month that is regarded as a consequence of regular overuse of headache medication in a patient with a pre-existing headache.18 The classification does not include the number of drug units or dosage used, but the number of days per month the drug is taken.
Whether medication overuse is a separate secondary headache rather than a complication of a primary chronic headache (migraine or tension-type headache)14 is still debated. Medication overuse headache can occur in patients with an underlying secondary headache, but only exceptionally.11 All abortive headache medications taken regularly may lead to MOH.9,30 However, MOH must not be confused with immediate or delayed headache secondary to use of, exposure to, or withdrawal from other substances such as nitroglycerin, histamine, or caffeine.18
Reducing the dose and eventually discontinuing the overused medication are the natural first choices of treatment, but experts differ on the best way to do so. Among patients who manage to discontinue the overused medication, 50% to 70% will revert to an episodic headache pattern.9,11
In this Pain Clinical Update, we present MOH as a prevalent condition with huge individual and societal consequences, focus on the clinical aspects of this condition, and emphasize that it can be prevented and treated. This article is based on an unsystematic search in PubMed for criteria, guidelines, trials, and reviews of MOH followed by a discretionary selection of publications. Some of the references used as “clinical evidence sources” are commented on in the reference list.
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