What are the symptoms of a fentanyl (synthetic opioid) overdose?

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Last updated: April 11, 2025View editorial policy

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From the Guidelines

Fentanyl overdose symptoms must be recognized promptly to initiate lifesaving interventions, including administration of naloxone, as outlined in the 2024 American Heart Association and American Red Cross guidelines for first aid 1. Recognizing these symptoms is critical for prompt intervention. Key symptoms include:

  • Pinpoint pupils
  • Respiratory depression (slow, shallow, or stopped breathing)
  • Extreme drowsiness or loss of consciousness
  • Cold and clammy skin
  • Blue or purple discoloration of lips and nails (cyanosis)
  • Choking or gurgling sounds
  • Limpness of the body
  • Unresponsiveness to stimulation These symptoms occur because opioids, such as fentanyl, bind to receptors in the brain that control breathing, causing respiratory depression that can lead to oxygen deprivation and death if not treated promptly. Naloxone (Narcan) is the life-saving medication used to reverse opioid overdoses, typically administered as a 2-4 mg nasal spray or intramuscular injection 1. If you suspect someone is overdosing, call 911 immediately, administer naloxone if available, perform rescue breathing or CPR if needed, and place the person in the recovery position (on their side) to prevent choking. Multiple doses of naloxone may be necessary as fentanyl is extremely potent, and the effects of naloxone wear off after 30-90 minutes. Even after naloxone administration, medical attention is essential as the person may return to an overdose state when naloxone wears off, as highlighted in the guidelines 1.

From the FDA Drug Label

The manifestations of fentanyl overdosage are an extension of its pharmacologic actions with the most serious significant effect being hypoventilation. The symptoms of a fentanyl overdose include hypoventilation, which is the most serious effect.

  • Other symptoms are not explicitly mentioned in the label, but it can be inferred that they may be related to the extension of fentanyl's pharmacologic actions. Treatment for overdose is focused on addressing hypoventilation and may involve administration of a narcotic antagonist such as naloxone 2.

From the Research

Fentanyl Overdose Symptoms

  • Fentanyl overdoses can cause severe respiratory depression, leading to respiratory failure and death 3
  • Symptoms of fentanyl overdose may include:
    • Respiratory distress
    • Cyanosis
    • Unresponsiveness
    • Cardiac arrest
  • Fentanyl can produce profound rigidity in the diaphragm, chest wall, and upper airway, leading to a condition known as "wooden chest syndrome" (WCS) 3
  • WCS is almost routinely fatal without expert airway management

Treatment of Fentanyl Overdose

  • Naloxone is commonly used to treat opioid overdoses, including those caused by fentanyl 4, 5, 6, 7
  • However, some studies suggest that naloxone may be ineffective against centrally mediated noradrenergic and cholinergic effects of fentanyl, which can cause severe muscle rigidity and airway compromise 3
  • Higher doses of naloxone may be required to resuscitate patients after fentanyl overdose, particularly in cases where carfentanil is involved 6
  • A study found that the naloxone dose required to treat an opioid overdose is not associated with the presence of fentanyl on urine drug screen 7

Outcomes of Fentanyl Overdose

  • Fentanyl overdoses can have severe outcomes, including death 4, 5, 3
  • A study found that mortality within 24 hours of fentanyl overdose was low (0.2%) in patients who received out-of-hospital naloxone and were treated in an emergency department 4
  • Another study found that mortality within 48 hours of opioid overdose was infrequent (0.081%) in patients who were treated with prehospital naloxone and released at the scene 5

References

Guideline

Guideline Directed Topic Overview

Dr.Oracle Medical Advisory Board & Editors, 2025

Research

Higher naloxone dosing may be required for opioid overdose.

American journal of health-system pharmacy : AJHP : official journal of the American Society of Health-System Pharmacists, 2019

Research

Naloxone Dosing After Opioid Overdose in the Era of Illicitly Manufactured Fentanyl.

Journal of medical toxicology : official journal of the American College of Medical Toxicology, 2020

Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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