I can't find it at the moment (edit: found it [2]), but I am sure I read something about Jerome Lettvin [1] doing some experimenting with CO2 but for something like schizophrenia, and that despite having good results he had to stop due to legal liability reasons or the like. I think it came up in an interview with him which I read a transcript of.

[1] https://en.wikipedia.org/wiki/Jerome_Lettvin

[2] https://www.mindstrengthbalance.com/learn/interviews/jeromel... (search for Laszlo to find the bit where they start talking about this)