Yep. That's why I'm surprised that fentanyl and similar compounds haven't completely taken over the illicit opioid market. I guess old habits (and supply chains) die hard.
Because fentanyl is far inferior to most opioids as a recreational drug. Firstly there's the problem of potency, if it isn't cut exactly right to distribute the fentanyl evenly amongst the cutting agent, you can easily end up shooting a portion of the powder stronger than it's supposed to be and OD, given that it doses in the microgram range (I found 1mg of fentanyl citrate to be equivalent to 100mg of morphine, give or take, and there's a second variety - phosphate maybe? - with a higher potency still).
This extreme potency also drives your tolerance up faster than other opioids do, for reasons I don't understand (I'd love it if someone who knows more about neurochemistry could explain though, it would seem that an equipotent dose would result in an equal tolerance increase, but it doesn't seem to work that way). Using it habitually for an extended period of time will give you an absurd tolerance and make using less potent, more traditional opioids difficult, if not impossible.
Secondly, it has a fraction of the half life of most other opioids, you need to redose every 60 - 90 minutes (if not more frequently), which makes sleep almost impossible when you're physically dependent, as opposed to redosing every 4 - 8 hours with heroin, and the more frequent injections destroy your veins faster (if you're an IV user, as most opiate addicts end up). For the 4 days and 3 nights I was injecting the diluted powder, I averaged maybe 3 hours of very disturbed sleep every night.
Finally in terms of the effects themselves - it has a powerful sedating/respiratory depressing effect, combined with (or giving it) a therapeutic index being much slimmer than more conventional opioids - in my experience. A 10% difference in dose with something like oxy or morphine was never a problem for me, I'd just nod slightly harder, but with fentanyl a 10% difference in the dose meant I'd pass out within 30 seconds of the shot and wake up with blood running down my arm half an hour later, which could easily be fatal if someone passed out in the wrong position or vomited and asphyxiated while unconscious. Or 10% lower meant I'd feel unsatisfied with the shot and feel the urge to top up, which is even more dangerous.
Finally, it's only marginally euphoric, often bordering on dysphoric, as most fully synthetic opioids seem to be (at equipotent doses, I'd say codeine is more euphoric than fentanyl, let alone heroin/morphine and the *codone/*morphone varieties). To be blunt, the high fucking sucks. It feels closer to some kind of weird xanax/methadone mashup, or a strongly sedating benzo with analgesic properties, than any of the actually fun opiates. As you can imagine, this would lead people to redose or use higher doses to try and get the buzz they're used to from other opioids, resulting in overdose.
All of this combines into an extremely dangerous drug that isn't all that enjoyable to use, compared to traditional opiates. No point in a drug that's easy to make if you kill off your user base.
That said, it's definitely out there on the market if you know where to look, both pure and in various diluted forms (tabs, powder being the main ones), but it's a niche thing for people who don't have access to or can't afford other opioids (being quite a bit cheaper because demand is lower).
Despite all that, I know there's at least one country somewhere around Eastern/Northern Europe (Estonia, iirc) where 3-methylfentanyl is the only opioid available as a street drug, presumably they're too far from traditional heroin distribution chains (and very careful with diluting their product, as 3-methylfentanyl is several hundred times more potent than fentanyl itself). And maybe the 3-methyl variety is more euphoric, I wouldn't know.
