Background: Medication overuse headaches (MOH) include headaches that last more than 15 days a month and usually occur after long-term use of analgesic. Most methods of medical treatment are ineffective. In some studies, great occipital nerve block is used to treat the headaches.Methods: This double-blind experimental study was performed in adult patients with MOH who attended Sina Hospital in Tehran from June 2009 to June 2011. Greater occipital nerve (GON) block was done in the two groups of patients by administering a combination of 3 ml of 0.5% bupivacaine and 2 ml of 5% saline or 3 ml of 0.5% bupivacaine and 80 mg of methyl prednisolone. We evaluated headache severity by Visual analog scale (VAS) and recorded days without headache. If patients were taking pain medications, preventive medications were given as usual before and after the injection. Student's t-test was performed for statistical analysis and a P<0.05 was considered significant.Results: Overall, 13 male and 19 female patients with a mean age of 39.88±8.76 years participated in the study. The mean reduction in headache severity one hour after injection was 5.56±1.03 and 4.63±1.92 in the first and second groups, respectively. Average days without headache one month after injection were 8.75 and 4.75 days in the first and second groups, respectively. There were no significant differences between the two groups.Conclusion: Both methods seem to be effective in medication overuse headaches treatment. This finding is important as non-responders to conventional methods will otherwise have a decreased quality of life.