1. The ex-drug addict has relapsed and started doing drugs again.2. My husband, a recovering alcoholic, was sober for two years and he relapsed (into drinking) and went in for treatment for a month.3. His cancer came back. or His cancer returned.
 relapse come back returnrelapse 用在人後面，表示此人的舊的壞習慣(如毒癮)或舊的病情復發，通常 relapse 後面不加任何字，如 The ex-alcoholic relapsed.a recovering alcoholic = 一個正在戒除酒癮的人如要指某病復發，如癌症，可說 His cancer came back.
It gives the illusin that you've computed the entire answer immediately.