Fentanyl is a member of the class of drugs known as fentanyls, rapid-acting opioid (synthetic opiate) drugs that alleviate pain without causing loss of consciousness (analgesic). Fentanyl depresses central nervous system (CNS) and respiratory function. Exposure to fentanyl may be fatal. Fentanyl is estimated to be 80 times as potent as morphine and hundreds of times more potent than heroin. It is a drug of abuse. Fentanyl (and other opioids) could possibly be used as an incapacitating agent to impair a person’s ability to function. In October 2002, the Russian military reportedly used “a fentanyl derivative” against terrorists holding hostages in a Moscow theater; 127 of the hostages died. (It is unclear whether the gas used also included other chemical agent(s).) Fentanyl is odorless.