"Therapeutically", hah, I've told myself that's what I'm doing but it invariably doesn't turn out to be very therapeutic and mostly I just end up needing actual therapy to get over it.

Last time was almost 3 weeks ago and probably precipitated the darkest and most acute period of profound distress and sadness that I can remember in a very long time. I have abused ketamine though, frankly, and it has always been pro-depressive for me although for some reason despite a vague awareness of this fact I have continually returned to it. If you can have a profound experience from 84mg then you are obviously not anywhere near my own (probably perma)tolerance, so despite my own experience I don't want to sound like I am completely dismissing it, (es)ketamine IS therapeutic for some people, it can be very valuable. I have had many profound experiences using ketamine - but I really have to be honest that my usage was probably always escapist, and recreational. The overlap with dissociatives and psychedelics for me just provided a way to convince myself that it was anything other than that, and I can say fairly confidently that it never actually improved my life outside the immediately comforting bounds of dissociation.
My sense is that this is a fairly common delusion of the entire class - I actually have yet to hear anyone convincingly say that ketamine was itself instrumental in truly improving their life in the longterm, except those who are using it for physical pain relief. Of course, using it for the alleviation of psychological sufferring is a type of pain relief - and again I don't rule out that this can be done, I believe there are good reasons that it is an approved medicine, although the recent approval and legitimisation of it with the Spravato brand is really just kind of incidental as far as I'm concerned, the medicinal properties it does hold, it held before Spravato existed and remain unchanged, if hopefully a little more studied. I guess I just hope to sound a note of caution, as well as a medicine it is a potent inducer of the delusion that it is beneficial when objectively it quite clearly isn't for many individuals, and this makes attempts to use it therapeutically fairly dangerous. But, anyone who can use it therapeutically for any sustained length of time, and can honestly say that their experience does not match my own at all - obviously still be careful, but I'm glad it works for some and am also very interested in hearing about these experiences, so please do report back.
For myself though this recent quite profound darkness has to be a clear red line, this isn't the first time I've professed I'm not gonna touch it for a long time and reneged on my own promise but for me this time really needs to be different, it just doesn't work for me.