For example title is great, but there's a bunch of other stuff to be aware of in there. E.G. "the most common solicited AE was headache in 33 of 50 participants (66%) receiving psilocybin and 13 of 54 participants (24%) receiving niacin."
Also this study was only 6 weeks. I think the obvious question is "Then what, do you redose, or hope it lasts?"
Lastly, anecdotally, I know a lot of people who recommended hallucinogens personally, and many/most of them seemed believably happier, but perhaps had other negative side-effects that a study like this wouldn't measure (e.g. do you friends think you're acting kinda weird now?). Some of these people seemed overly invested in convincing me in a way that made me uncomfortable and uncertain of their objectivity.
There's an interesting reply-all episode about microdosing LSD. https://gimletmedia.com/shows/reply-all/2oh933