text_1: 然而 , 如果 当地 研究者 认为 经 预防性 用药 , 慢性 偏头痛 患者 的 每月 头痛 天数 少于 15 天 , 则 可 参加 本 试验 .
  
text_2: however , if the opinion of the local investigator was that participants with chronic migraine had fewer than 15 headache days per month because of concomitant preventive treatment , the participants were eligible for the trial .
  