Sources
A fentanyl overdose can be caused by a single pill.
3. U.S. Drug Enforcement Administration. (n.d.). Facts about fentanyl.

Naloxone is not a substitute for emergency medical care. Administer naloxone in accordance with the manufacturer’s instructions. When administering naloxone nasal spray, always be sure to call 911 right away, even if the person wakes up. Keep the patient under surveillance or close watch. If breathing does not return to normal or if breathing difficulty resumes, after 2 or 3 minutes, give an additional dose of naloxone nasal spray using a new device in the alternate nostril. Repeat doses of naloxone may be necessary.NARCAN® is a registered trademark of EMERGENT OPERATIONS IRELAND LIMITED PRIVATE COMPANY.