As @kerkeslager states below, this is just not true. I think the best way to understand a placebo effect is this: If I don't give 100 patients a drug to cure a

As @kerkeslager states below, this is just not true. I think the best way to understand a placebo effect is this: If I don't give 100 patients a drug to cure a cough and 30% stop coughing, I have a baseline. If I give 100 patients a drug to cure a cough and 90% stop coughing I can say my drug is effective. If I give 100 patients a sugar pill and tell them it will cure a cough and 60% stop coughing I can say this is better than my baseline and the placebo effect is present. If I give 100 patients a sugar pill and tell them it will cure a sneeze and 60% stop coughing and nobody stops sneezing, then I need to revisit my previous study to find out if sugar can cure a cough. But in this case you don't have a placebo effect because the patients believed the pill was to address a sneeze.