There are also studies that test against placebo. There have been lots and lots of trials on these things with different designs that make different cost/benefit tradeoffs.
A difficult one with psychedelics is as-mentioned: people can easily "break the blind". But if you want to eliminate that problem you can instead do a micro vs macro dose, in which case you're measuring a slightly different thing.
A difficult one with psychedelics is as-mentioned: people can easily "break the blind". But if you want to eliminate that problem you can instead do a micro vs macro dose, in which case you're measuring a slightly different thing.