I've used ketamine to treat suicidal ideation. It only lasts a few days at first, but with repeated use the effects last longer. I haven't used it in almost a year.
It really was like a switch was flipped in my brain.
There's a large subset of the population for whom it doesn't act as an antidepressant but it does alleviate suicidal ideation. I'm in that group.
A recent med change caused some suicidal ideation and I'd forgotten how emotionally exhausting it is after not having experienced it for so long.
There are a lot of exciting implications. It is further evidence for what we've seen with SSRIs and other meds causing suicidal ideation, that there's overlap with depression and suicidal ideation, but they are two different phenomena.

It's not really published in the literature, but it's "common knowledge" among clinics and stuff that if you're on benzos it won't work. There are also studies testing whether naltrexone, an opioid antagonist, prevents the effect (trying to figure out the mechanism by which it works). I haven't seen the results published, but from what I've heard secondhand through the grapevine they're finding that it does prevent the antidepressant effect from working. So the mechanism is probably at least somewhat opioid mediated.

As for access, I went with IM not intranasal because I wasn't convinced of the efficacy of the nasal route based on the research at the time, and I acquired it via alternate means...