But this of course introduces more uncertainty, as you pointed out, so to have any conclusive results a much larger sample group would be needed, I think.
Also I agree with others that comparison with the baseline for each test subject, not just between the test group and control group, would be important.
(note - "in mice")
I think this research was not done in the US but in another country (not sure which one?), not sure if research norms or availability or what differ there.
I think there may be that if they isolated psilocybin, they could have missed other compounds that play a part in causing desired effects. Obviously this is a different substance than cannabinoids, but I think when it comes to plants it makes more sense to test it exactly how subjects use it rather than use synthetics.
edit: I hope I didn't cause offence to any mushroom - of course they are not plants, but I hope you get my point.
* https://www.vice.com/en/article/93a5x3/judges-deny-challenge...
This is the main reason with psychoactive mushrooms overall. You can't dose exact via bio material so overdosing happens regular and could be actually harmful.
https://www.reddit.com/r/IAmA/comments/allg3/i_used_lsd_and_... (I see this is anecdotal as well)
Its hard to find serious papers about it because most of the time its due to "abuse" of drugs and (!) mixed consums.
Anyways, I had a friend who was really into mushrooms overall (not only psychoactive ones) and while he was pretty open to drug using he stated multiple times that overdosing can lead to bad trips and so called "hängenbleiben" (I dont now the english term, it means the trip never really stops).