I had the chance to work with this stuff some time ago.
1.3mg seems a little low for an oral dose. 10-20mg was a good starter dose for me with no tolerance (oral). With 20 being enough for a nod. With tolerance I've tested it up much higher, and have experience with: oral, nasal, plugging, vaping the HCl and freebase, and IVing the HCl. I've gotten effects from as little as 2-5mg, but they were weak at best.
Highest dose tested was 60mg IV with a fairly high tolerance (this stuff builds tolerance very fast due to its short duration). When taken IV I find this stuff more euphoric than Morphine, Heroin, Butyr-Fentanyl or any other opioid I have experience with, however the duration is extremely short, 40-60 minutes after a shot before you're really craving another shot. When snorted or plugged the duration is much more acceptable, with a 2-4+ hour peak depending on the dosage, 3-4 being average. Oral lasts longer, 5-7 hours, but is significantly less potent and lacks the rush that's present with other ROAs.
Even snorted has a rush comparable to smoking and IVing some other potent opioids, so this stuff can be incredibly euphoric, but I'd test your stuff out and see how the burn is, I'm not sure if the stuff I had was a batch with a weird pH or if the chemical is inherently caustic or what but I found that with the stuff I had that adding a tiny bit of baking soda seemed to help, so my guess was low pH (highly acidic).
This also seems to be a Marmite (aka: love it or hate it) drug. Everyone I know who tried it either found it incredibly euphoric and comparable to the likes of Heroin, or found it to be lacking/missing something. I have a feeling there is some kappa-opioid activity with this one and that's why it's somewhat different from other opioids. It also builds tolerance in a weird way, as tolerance to this drug itself builds up massively, and seemingly other opioids are very weak while you're on it, but once you come off it your tolerance to opioids seems to have dropped massively within 24 hours as if it were lower than what it was before you took this stuff. In fact I had something similar to precipitated withdrawals a couple of times when I dosed this stuff after taking other opioids (well, one other: Dihydrocodeine), which makes me wonder if it has a super high binding affinity like say Buprenorphine and either lower mu affinity or some kappa affinity to interfere with the mu-opioid effects.
All in all a very interesting substance but one I'd handle with extreme caution, if smoked or IVed this is one of the most fiendish and addictive opioids I've tried alongside the likes of Heroin and Butyr-Fentanyl. With other ROAs at lower dosages it can be a fairly good taper/maintenance drug if you have good willpower but I'd advise dilution (and maybe adding baking soda?) if you receive stuff that burns your tissue when snorted/plugged/etc, because I nearly tore a hole through my nasal passages with this stuff when I hammered a few grams of it through my nose in a few weeks before.
Also on a final note, regarding the potency:
- As a pain killer, the 7.5x Morphine figure is definitely accurate, if not more - even tiny doses like 3mg or so have a noticeable painkilling effect with low tolerance, even if you feel no high you'll feel as numb as you would on a full dose of Morphine.
- In terms of actual recreational dosage, I think that number is a bit high, I'd say it's more like 3-5x the potency. i.e. 20mg IV U-47700 is similar to 60-100mg IV Morphine. That's still highly potent though and I'd be very careful with this stuff, don't play around with it if you don't have decent milligram scales and/or a known initial weight alongside liquid measurement, or get it in pill form if available.