Both of those illicit fentanyl and carfentanil are really risky opioids that will bring about a quick overdose and death when abused, but carfentanil is much more potent than fentanyl. Numerous doses of your anti-overdose drug naloxone (Narcan) will not be effective to reverse an overdose. Carry on reading throughNEONATAL OPIOID WITHDRAWAL SYNDROME