The investigators propose enrollment of patients upon or shortly after presentation to the emergency department for treatment with ketamine or placebo. 30 minutes after study drug is administered, patients will have the option to request rescue medication which will be ordered by the treating physician according to standard emergency department protocol. Pain scores will be documented using the Numerical rating scale (NRS-11), 4-Point Pain Intensity Categorical Scale, and 4-Point Functional Disability Scale at 0 minutes, 30 minutes, and 60 minutes post treatment. Follow-up telephone calls will be made 72-120 hours after treatment to assess the incidence of recurrence of head pain and patient satisfaction with the treatment.