"Fentanyl is a synthetic opioid analgesic acting predominately at the μ-opiate receptor. It has historically been used as a pain reliever and an anaesthetic in both human and veterinary medicine and in terms of analgesic activity it is at least 80 times more potent than morphine. Fentanyl was first synthesized by Paul Janssen in 1960 and marketed as a medicinal product for treating pain. Subsequently, many fentanyl analogues were developed including sufentanil, alfentanil, remifentanil, and carfentanil.