Does a single oral dose of dexamethasone after successful emergency department treatment of migraine reduce the incidence or severity of rebound headache within 48 hours?

INTERVENTION: The primary aim is to compare the proportion of patients who experience rebound headache within 48 hours after ED treatment of migraine between a group treated with single dose oral dexamethasone 8mg and a group treated with placebo.Secondary aims are to compare headache severity, analgesia/ health service use, adverse events and return to normal functioning between the groups. CONDITION: Migraine PRIMARY OUTCOME: Proportion of patients who were discharged pain free that have a recurrence of headache within 48 hours Proportion of patients who were not pain free at discharge whose headache is worse or unchanged within 48 hours SECONDARY OUTCOME: Adverse events and return to normal functioning between the groups. Analgesia/ health service use Comparison of headache severity. INCLUSION CRITERIA: Consenting adult patients with physician‐diagnosed migraine treated in the ED who are willing and able to be contacted between 48‐72 hours after discharge for follow‐up.