Per my other comment in this sub-thread, my concern there is that the experimental group will still be getting whatever it is that's bad, and in the context of

Per my other comment in this sub-thread, my concern there is that the experimental group will still be getting whatever it is that's bad, and in the context of "unwanted permanent mental health effects" of recreational use the experiment would be unethical. On the other hand, with the recent state-wide decriminalizations we're "conducting" a rather while uncontrolled experiment right now that ought to be able to yield better data on the biggest concerns, although that sort of epidemiological research is really, really hard, and few are unbiased.