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Objective: The aim of this study is to critically analyze the evidence of the efficacy and safety of greater occipital nerve (GON) block for the preventive treatment of chronic migraine (CM). Background: A rigorous scientific assessment of efficacy and safety of the GON block for preventive treatment in CM is not available. This critical review was undertaken for this purpose. Methods: References for this review were identified by searches of articles published in the English language in PubMed between 1969 and April 15, 2020 using “greater occipital nerve block,” “chronic migraine,” “migraine,” “headache,” and “treatment” as keywords. Results: Out of potential 532 articles, 9 open-label and 4 placebo-controlled trials that studied the role of GON block for prevention of CM were identified and reviewed. Open-label trials reported a reduction of headache severity and frequency in 35–68% of patients. The beneficial effect of a single block lasted up to 4 weeks. Randomized controlled trials (RCTs) used varied methodology and techniques of GON block and the outcomes were reported at different time points. A single RCT showed a beneficial effect of the GON block at 1 week. However, the GON block was found to be safe and well tolerated. Conclusion: Long-term efficacy of GON block in CM shall need further well-designed RCTs using standardized methodology. This study, in addition, reviewed the limitations and uncertainties regarding the technique and methods of use of GON block in CM.
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