Controversy over the classification of medication-overuse headache.

Medication-overuse headache (MOH) is a relatively common and impactful disorder, affecting 1% to 2% of the population, characterized by daily or near-daily headache aggravated by chronic acute medication intake. Primary headache patients do not necessarily develop MOH after acute medication overuse, although a pre-existing primary headache is inevitably present. Likewise, headache patients may deteriorate in terms of frequency without medication overuse, or suffer from chronic headache in the presence of drug abuse without any causal relationship. To classify and define diagnostic criteria for MOH in the absence of objective biomarkers is a difficult task that is presently based on clinical grounds and is limited in part by the relative lack of research in this field. The present criteria are less restrictive but also less precise than the previous versions because they allow the diagnosis without the previously required MOH confirmation after medication withdrawal. MOH should remain as a distinct secondary disorder based on the available clinical and pathophysiological evidence.