I will chime in.
Regardless, I can't even find a paper about it anywhere. No binding affinities, no information about metabolism, etc.
This substance, at 10 mg rectally (U-51754) is overwhelmingly strong at the 10 minute mark and almost completely gone by 45 minutes, I swear I slipped into a mildly delirious state, I heard things that weren't there when nodding. Undoubtedly somewhat dysphoric with various degrees of auditory hallucinations while being extremely floored, some dissociation even.
This stuff has no legs. Keeps withdrawals away for maybe 2 hours before its yawning and teary eyes all over. Easy with this. I have tried orally, it lasts somewhat longer but is less potent.
potentially active at the κ-opioid receptors? I certainly suspect it, because it has a distinct incapacitating effect. It also raised my heart rate from 55 or so to about 90.
So this is breaking new ground. Tickles me funny I was probably the first to shove it up my arse.
P.S: this stuff belongs up your rectum. Dissolve in 10 ml of water or so and boof it. No irritation, rapid onset, and bypasses first pass metabolism.