What’s so interesting about this that I just learned after googling about Spravato that ketamine is a treatment for serious depression. Why? That’s fascinating! Is it the dissociative effects?
The Huberman Lab episode Ketamine: Benefits and Risks for Depression, PTSD & Neuroplasticity <https://www.hubermanlab.com/episode/ketamine-benefits-and-ri...> and the referenced journal articles (including the above) have a lot of detail on it.
https://lorienpsych.com/2021/11/02/ketamine/#11_How_does_ket...
the opiate receptor interaction might be important, but it seems that the antidepressant effect persists even if the opiate pathway is blocked (via naltrexone)
https://pmc.ncbi.nlm.nih.gov/articles/PMC6439824/ (though it's an open-label super small study ... n=4)