The chapter presents one of the most discussed synthetic anesthetics—fentanyl. The possibilities of its use, the effect on the health of users, pharmacological and chemical findings, the issue of human and veterinary use of these substances, and the comparison of the effects of its derivatives are described. It discusses the issue of the abuse of these psychoactive substances and their seizures by members of the rescue system and the necessity of legislative control. Some methods of detecting fentanyl-type substances are listed, both by simple orientation methods and by more sophisticated techniques of infrared spectroscopy and liquid and gas chromatography. Finally, fentanyl is discussed as an incapacitating agent in the protection of the population.