I suppose the theory was that it had to work near instantaneously so the terrorists wouldn't be unconscious by the time they realized they were being drugged. You wouldn't want them to have time to trigger bombs and shoot hostages before passing out. That part of the plan worked very well, by the way. It fell apart in the evacuation phase where the victims would be resuscitated by trained paramedics (anti-opioid exist that immediately cancel the effect (very useful for any paramedic dealing with overdose patients ... except that those patients immediately wake up and are then typically very aggressive because a very sweet dream was ended, and now they are back in the painful reality that they just wanted to escape)) because there were no trained paramedics on the scene, and rather than rushing the patients to the nearest hospital ASAP they orderly loaded regular buses and sent them off only after they were full of patients, which just took too much time.
Remember the Moscow Theater Hostage Crisis? It was fentanyl (sweet Lord why) they tried using to sedate everyone.
I read a different story. Usually this stuff shuts off your breathing reflex, so it's only safe to use in a hospital but the Soviets developed an improved version that that didn't have this drawback. So they thought it was safe to use. Except it wasn't for the seats. They had a low back rest. Anybody whose head dropped back suffocated because the tongue slid into the windpipe.
Edited by Markus Becker, Yesterday, 11:25 AM.