The evil twin of the placebo effect is the nocebo effect, when you give an inert substance and get an adverse reaction. Note that is different than a side effect. I give a patient penicillin and they get a rash, that is a side effect. I give them a product with no effect and they get a complication, that is a nocebo effect.\n"A nocebo (Latin for \u201cI will harm\u201d) is something that should be ineffective but which causes symptoms of ill health. A nocebo effect is an ill effect caused by the suggestion or belief that something is harmful."\nIt is why I was amused by Clinically meaningful nocebo effect occurs in acupuncture treatment: a systematic review.