The purpose of this study is to determine whether active repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex is safe and effective for preventive treatment of chronic migraine, compared to placebo repetitive transcranial magnetic stimulation.

Patients with chronic migraine according to the criteria of the International Headache Society will be randomized to either active repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex or placebo repetitive transcranial magnetic stimulation, in a total of 23 sessions of treatment (15 sessions in the first month and 8 sessions in the second month of treatment). Outcomes will be evaluated at baseline, after one, two months after treatment, and one month after end of treatment

Inclusion Criteria:

• chronic migraine according to the criteria of the International Headache Society
• no change in prophylactic medication in the past 3 months

Exclusion Criteria:

• other neurological disorders
• bipolar disorder
• alcohol or drug dependence in the past 2 months
• suicidal ideation, psychotic symptoms
• contraindications to transcranial magnetic stimulation (cardiac pacemaker, implanted electronic devices, metal in the skull, skull fractures, history of seizures)
• use of antidepressants in the past 4 weeks
• pregnancy or lack of birth-control method in women of childbearing age