“…Since 2002, four systematic reviews have been published on manual therapy for cervicogenic headache [55,191,192,216]. The reviews made inference based on six RCTs that evaluated a range of manual therapy treatments including spinal manipulation [217][218][219][220][221][222], mobilization [217,220], and friction massage [220,222]. Astin and Ernst [191] concluded that due to methodological limitations of the RCTs, it is unclear whether or not spinal manipulation is an effective treatment for headache disorders.…”