If you start with people who know what MDMA feels like, I suspect you're sunk for the reasons you state.
But if for instance the placebo were niacin... niacin makes most people feel funny. If you don't know what MDMA or a niacin flush feels like, you might just know something is happening but not what.
And then you test people who don't experience niacin flush with or without a placebo to make sure that niacin isn't a therapeutic chemical.
Blinding isn’t just about the patients - It’s about the therapy providers as well. We would like to think they’d provide the same treatment regardless of what the patient received but over-eager researchers tend to get more excited about the active group and provide them more attention and enthusiasm.
Niacin isn’t a great placebo these days because it’s not the 70s any more and people going into these studies will probably Google what to expect from the drug. Also Niacin is short acting and makes people itchy and uncomfortable, so it’s not really compatible with therapy.
But if for instance the placebo were niacin... niacin makes most people feel funny. If you don't know what MDMA or a niacin flush feels like, you might just know something is happening but not what.
And then you test people who don't experience niacin flush with or without a placebo to make sure that niacin isn't a therapeutic chemical.