Naloxone opioid overdose antidote, molecular model. This drug, marketed as Narcan, Nalone and Narcanti, is administered to counteract the effects of an opioid overdose, for instance of heroin or morphine. Opioids bind to opioid receptors in the central nervous system, and depress its activity. Respiration is slowed, sometimes to life-threatening rates. Naloxone binds strongly to opioid receptors, competing with and displacing the opioids. This reduces their harmful effects. In this model, atoms are represented by coloured spheres; carbon is green, hydrogen is white, nitrogen is blue, and oxygen is red.