A reader expressed concern that a statement in our article Naloxone (Narcan) Nasal Spray for Opioid Overdose (Med Lett Drugs Ther 2016; 58:1) might be misleading. We stated that heroin has a half-life of 2-6 minutes, which is correct, but heroin is a prodrug that is rapidly metabolized to 6-acetylmorphine and morphine. The risk of respiratory depression is related to those active metabolites, and it may persist well beyond the clearance of heroin from the blood.