>>16741793 (OP)Ketamine. I know it's somewhat of a "meme" these days, but it really does work. I used it recreationally years and years ago whilst being extremely depressed, and it completely ended my depression immediately. It would last for weeks, too. I remember being so surprised at how insanely effective it was for depression. Overnight id go from a 9/10 depression to waking up and feeling entirely fine. I'd describe it as a "soft reboot" where your assumptions and views on life become wiped clean and you get a second chance to build a new perspective. If my brain was a computer, it felt like it was clearing out processes that were using up too much resources or slowing it down.
Of course oftentimes I'd end up slowly becoming depressed again after several weeks. It only works imo in conjunction with sweeping lifestyle changes, but the benefit is that you're far better equipped to make those changes during the weeks of being not severely depressed.
I can also exclude placebo as an explanation, as this was before I'd ever once heard anything about ketamine being used for depression. It would be several years before I discovered that what I'd experienced with ketamine was actually a well documented and studied phenomenon.
To date, nothing has ever come close to level of both effectiveness, longevity, and speed of effect as ketamine has for my depression. Back then I would do very small doses regularly every few weeks or months, although important note is I did find it slowly becoming less effective if I did it too frequently.