This cold medicine is OTC, so you can buy it without a doctor's prescription.

OTC 是 "over-the-counter" 的缩写形式，由介词短语 over the counter（字面意思是"越过柜台"）演变而来。在医药领域特指"非处方药"，即不需要医生开具处方就能直接在药店柜台购买的药品。