Etorphine hydrochloride (6,14-endoetheno-7alpha-(2-hydroxy-2-pentyl)-tetrahydro-oripavine hydrochloride) is a semi-synthetic opioid derived from thebaine.
Availible as Immobilon or M99, it is used for the immobilization of ungulates-- primarily very large ones. Effects are typical of opioids. Its analgesic potency in humans is 1000 times that of morphine. Effects are reversed by opiod antagonists, esp Diprenorphine.
Abuse potential is somewhat limited by potency. It's the pan galactic gargle blaster of narcotics, and with injectable drugs, you don't get a slice of lemon around your brick.