N-COUNT (用于测试新药效力的)无效对照剂;(用以安慰想象自己得病的人的)安慰剂 A placebo is a substance with no effects that a doctor gives to a patient instead of a drug. Placebos are used when testing new drugs or sometimes when a patient has imagined their illness. (用于测试新药效力的)无效对照剂;(用以安慰想象自己得病的人的)安慰剂