Opioids are used rather frequently to immobilize big animal species in the natural reservations and the ZOO. Ultrapotent derivative of thebaine ? etorphine is used; it is 10 000x more effective then morphine in some animal species.
The derivative of fentanyl ? carfentanyl is more potent; it is used in the U.S.A. The other derivatives of fentanyl - thiafentanyl and sufentanyl (the lower frequency) ? are used from the opioids family.