It took him three years to recover from drug addiction.

drug 指"毒品、药物"，这里特指成瘾性药物。 addiction 是名词，来自动词 addict（使上瘾），后缀 -ion 表示状态或行为，指"成瘾、上瘾的状态"。 drug addiction 指"对药物的依赖性成瘾"，即"毒瘾"。