naloxone UK /nəˈlɒk.səʊn/US /nəˈlɑkˌsoʊn/ noun1 •An opioid inverse agonist used to counter the effects of an overdose on opioids (such as heroin or morphine).Neffy uses the same spray device as Narcan, the naloxone nasal spray for opioid overdose, according to a spokesperson for its maker, ARS Pharmaceuticals. — 2024 formsnaloxones