From that paragon of information known to be false, but is believed by the editors to be true, regardless of the actual facts:
This is the list of Schedule I drugs as defined by the United States Controlled Substances Act.[1] The following findings are required for drugs to be placed in this schedule:[2]
1) The drug or other substance has a high potential for abuse.
2) The drug or other substance has no currently accepted medical use in treatment in the United States.
3) There is a lack of accepted safety for use of the drug or other substance under medical supervision.
I see the LSD is listed as Schedule 1. Guess somebody doesn't know that it is/was effective, when used to treat various psychological issues. The issue for the clinician is doing an accurate psycho-diagnostic exam. Something that takes roughly 3 hours of patient time, and another three or so hours, sifting the results.
Mescaline can be legally used for religious purposes. Come to think of it, it also has been used for psychotherapeutic reasons.
Again, it works as a psychotherapeutic agent, when used for the appropriate condition, which takes roughly 3 hours of patient time, and three or more hours sifting the results.
IOW, the therapeutic treatments are known, but current medical practice in essence, prevents the diagnostic to be made. (Let's face it, when you have 180 seconds with a client, one can not do a differential diagnosis, much less an accurate one., And insurance companies are doing their utmost to reduce client face-time to 60 seconds, or less. )