Morning.
I had to check these dates of these posts twice to ensure I wasn't looking at a corpse thread or something posted like decades ago and I missed it. And far be it for me correct information furnished by a moderator who has been around for over a decade. But in this particular case I think it warranted. And I suppose in fairness: we all have our own drugs interests and therefore will have spent more time researching a particular drug over another e.g. don't ask me anything about meth. because I wouldn't have the answer given that its interest to me is limited purely to the commercial value.
The above all being said: I'm posting this in the true spirit of harm reduction i.e. lest some new user or guest browsing comes across this information and goes on a quest to obtain Carfentanil (sometimes spelled Carfentanyl) assuming it to be the shit based on the information contained on this thread.
Although the generally quoted figures vary some (usually not by much though): Carfentanil is 100 times stronger than Fentanyl, 5 000 times stronger than Herion, and a heroic 10 000 times stronger than Morphine. It was first synthesized in 1974 and became commercially available in 1986 being sold as an anesthetic for veterinary use (to anaesthetize large mammals e.g. elephant and rhino to name but two). It has further been weaponized i.e. used by the Russians in 2002 during the Moscow theater hostage crisis. It only became a controlled substance in China in 2017 (but of course not to be outdone and in true Chinese fashion is still being manufactured and can still be purchased the caveat, as usual, being the purported purity of the powder available).
I'm not going to re-type the entire Internet here. But the above should give you a rough idea as to why it's probably not a good idea to source and use.
One or two anecdotes:
Yip. It would be measured in µg (micrograms). Given that I know personally what 16.8µg of Fentanyl looks like (almost imperceptible) well then I don't know how you'd calculate a dose save for making a measured solution in order to calculate the per ml concentration.
The generally accepted lethal dose of Fentanyl for an average human being is 2mg. Based on this: you do the math (as to what the possible lethal dose of Carfentanil could be) (although if it's any consolation it's, oddly enough, less deadly in rats than Fentanyl itself and for a variety of reasons but which I doubt are applicable here).
It may interest some to know that the "duration of action" is a different thing altogether to the elimination half life of a drug (although they are to a degree linked). Also interesting to note that the elimination half life of a drug differs depending on the route of administration (believe it or not).
Anybody wanting to put this to the test: may as well go for broke then i.e. Ohmefentanyl anyone? Lol!
Edit:
For the sake of interest and as usual trying to do a thorough job of things see the document below. Sadly it's dated (2017) but is a report from the WHO re: Carfentanil. Pretty much everything you want to know really all nicely summed up (and some interesting factoids that even I was not aware of until now).
Carfentanil - Critical Review Report