The study found that fentanyl, which is typically prescribed to treat severe or chronic pain, is a powerful synthetic opiate approximately 50 times more potent than heroin and 100 times more powerful than morphine. In recent years, clandestinely produced fentanyl in combination with heroin or cocaine has been linked to hundreds of deaths and overdoses. Because fentanyl is an opiate and specialized testing is required to detect it in biological samples, many fentanyl overdoses were initially classified as heroin overdoses. The NFLIS is a program sponsored by the Drug Enforcement Administration (DEA) Office of Diversion Control that systematically collects drug identification results and associated information from drug cases analyzed by Federal, State, and local forensic laboratories. These laboratories analyze substances secured in law enforcement operations across the country and represent an important resource in monitoring drug abuse trafficking. National and regional estimates for fentanyl are presented as well as information on fentanyl combinations reported by State and local laboratories. Supplemental information for these years is also presented from DEA’s system. Tables, figures, and appendix