Brief Intervention for Medication Overuse Headache

The investigators will perform a cluster randomised controlled study of Brief intervention (BI) for medication-overuse headache (MOH) versus business as usual. GPs will be trained to perform a structured brief intervention after identifying patients with probable MOH using the severity of dependence scale. The control arm will include patients of GPs who have not been trained in BI. Patients will be recruited by prior short postal screening of patients listed on the GPs patient lists. The hypothesis is that BI will lead to improvement of medication-overuse and chronic headache as compared to no BI. Main outcomes are: * number of medication days per month * number of headache days per month * headache index