Migraine headache can be a debilitating condition. A small but significant proportion of sufferers seek treatment in emergency departments [ED], accounting for 2-5% of ED visits.Available data suggests that up to 66% of these patients may experience rebound headache after discharge that affects their ability to function normally [eg work, social, etc].It appears that inflammation plays a key role in recurrences. A number of small studies suggest that a single dose of corticosteroids at the time of discharge might prevent rebound headache. To date these studies have used intravenous dexamethasone. The aim of this project is to determine if a single dose of oral dexamethasone at the time of discharge from the ED [after successful treatment] prevents rebound headache.