[sleepytimetea]

What is unclear to me is why they were never approved for human medical use when discovered/invented in the 50s - did the clinical trials uncover some toxic side effects ? It must be common knowledge to some chemists out there why the entire class of -azenes was abandoned then ?

[Workaccount2]

It seems that clinical trials unveiled that the drugs themselves were too toxic to be safely used, being many times stronger than even fentanyl.