Clinical studies provide evidence that ketamine and psilocybin could be used as fast-acting antidepressants, though their mechanisms and toxicity are still not fully understood. To address this issue, we have examined the effect of a single administration ...
www.ncbi.nlm.nih.gov
I haven't looked at the Ketamine research stuff, but I will say this anecdotally.
I have titrated ketamine drips on chronic pain patients for sometimes 72 hours straight.
Many of these patients also have depression.
None of these patients have ever said anything about suddenly feeling like a new person after I've stopped their drip. In fact one talked of suicide. And I know of two patients that had received multiple ketamine infusions for chronic pain over past months that ended up committing suicide not long after.
More than a few times I've titrated to high enough levels where the patient starts to become fearful ("I am not feeling well, this does not feel good, I am feeling really weird and not in a good way,") etc. and we have to back off quick.
I don't know how to what degree they are dosing people for depression, but I have heard it's not enough to put someone into a k-hole (which is not fun by any account I've heard).
Thus I am rather skeptical.