Ketamine!
Via IM injection, obviously. I couldn't afford any sort of fancy specialty-clinic ketamine treatments for depression, so I took to injecting 80mg every Monday with no inter-dose usage malarkey. I will forever remember it as one of my most functional months to date; though, now that I think about it, all I can remember from that period was injecting K and flubbing my way through my first few NA meetings.
My only two experiences with IV injections came at the hands of doctors...
First time?
A mixture of midazolam, fentanyl, and propofol. You better believe that the roughly two seconds I was conscious were just PEACHY. As were the first five or ten minutes after I came out of the propofol.
Second time, 5mg morphine x2 (10min apart) in the hospital, to alleviate ulcer pain. Thoroughly underwhelming; great analgesia, zero euphoria, intense nausea even with a 15 second push.
Nausea?! The only other time I've experienced opioid-induced nausea was 3+ years and many, many morphine-milligram-equivalents earlier, and the dosage of intrarectal U-47700 in that instance was about equal to 120mg oral morphine.
But even in the case of the underwhelming 10mg IV morphine... I could see the addictive potential in the speed by which I achieved even non-euphoric pain relief. To go from "suffering" to "suddenly devoid of pain" in a few seconds flat was a neat trick.
The sick fucks gave me haloperidol shortly thereafter and ruined the morphine though, l o l. By dint of the horrific akathisia I now know haloperidol gives me... what, I'm not good enough for ondansetron?! Not their fault and not Zofran's usual indication but JESUS, from morphine-calm to EPS hell just like that.