“给服药”常见的英文表达是 “administer medication” 或 “give someone medication”。
administer medication：较为正式和专业，常用于医疗、护理等场景。例如：The nurse administered medication to the patient according to the doctor's orders.（护士按照医生的嘱咐给病人服了药。 ）
give someone medication：比较口语化、日常化。例如：I need to give my child some medication for his fever.（我得给孩子吃点治发烧的药。 ）