The doctor prescribed this medicine to be taken twice a day.

prescribed 是动词 prescribe 的过去式。prescribe 由前缀 pre-（表示"预先"）和词根 scribe（写）组成，字面意思是"预先写下"，引申为"开处方、规定"的意思。在医疗场景中特指医生开具药方。