She started self-medicating with coffee and painkillers to cope with stress, which isn't a healthy solution.

self-medicating 是由 self（自己）和 medicate（用药治疗）组成的复合动词，加上 -ing 变成现在分词形式。self 表示"自己"，medicate 来自 medicine（药物），意思是"用药治疗"。self-medicating 指"不遵医嘱而自行用药"的行为。