Both illicit fentanyl and carfentanil are extremely hazardous opioids that may bring on a quick overdose and death when abused, but carfentanil is more powerful than fentanyl. Numerous doses with the anti-overdose drug naloxone (Narcan) will not be effective to reverse an overdose. Carry on readingNasal Spray: Store at as many as 25C; do not freeze