definition for narcan
naloxone(Noun) A drug used to counter the effects of an overdose on opioids (such as heroin or morphine). Naloxone. Naloxone is an opioid inverse agonist drug developed by Sankyo in the 1960s. Naloxone is a drug used to counter the effects of opiate overdose, for example heroin or morphine overdose. Naloxone is specifically used to counteract life-threatening depression of the central nervous system and respiratory system.