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Carfentanil vs Fentanyl: Which is more dangerous?

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Aug 16, 2022.

Official answer

  • Both illegally-made fentanyl and carfentanil are extremely dangerous opioids that may result in a quick overdose and death when abused, but carfentanil is more potent than fentanyl. Multiple doses of the anti-overdose drug naloxone (Narcan) may not be effective to reverse an overdose.
  • Carfentanil has been shown in animal studies to be 100 times more potent than fentanyl and 10,000 times more potent than morphine.
  • Carfentanil has NO medical use in humans. It is an analog of fentanyl and is used as a tranquilizer in veterinary medicine for elephants and other large animals.
  • These drugs can pose a significant threat to first responders and law enforcement personnel.

The lethal dose for carfentanil in humans is not known; however, it is 100 times more potent than fentanyl. Fentanyl is known to be lethal at the 2 milligram range, depending upon your body size, opioid tolerance, and former usage. Fentanyl can kill you within a matter of 2 minutes, usually due to respiratory failure (breathing that has stopped).

Where is carfentanil found?

Synthetic fentanyl is made in illegal labs and sold on the streets as a powder, as a liquid placed on blotter paper, put in cocaine or heroin, placed in eye drops or nasal sprays, or made into pills that look almost exactly like other prescription opioid painkillers.

  • Just like fentanyl, carfentanil has been reported to be found in illicit street drugs. These opioids may be commonly found cut or mixed into street drugs like heroin, illegally manufactured pills, crystal meth, cocaine or crack, and has been fueling the overdose epidemic in the U.S.
  • In a 2017 study from the Centers for Disease Control and Prevention (CDC), carfentanil was identified in 21 of 288 (7.5%) overdose deaths due to fentanyl analogs in various counties in Ohio.

Street carfentanil first appeared in the early 2000s, and there has been an escalation in cases. A tiny, almost invisible amount of the drug is deadly.

Lethal Dosage: heroin vs fentanyl vs carfentanil

Source: DEA, 2022 Lethal doses of heroin, carfentanil, fentanyl

Will naloxone reverse a carfentanil overdose?

  • Naloxone can be used to help reverse an overdose for carfentanil, but multiple doses of naloxone or even continuous infusions may be required to reverse the opioid action, if possible.
  • First, give a dose of naloxone right away and then immediately call emergency medical services (such as 911).
  • Turn the person on their side to lessen the chances of choking. Stay with the person. Continue to administer a dose of naloxone every 2 to 3 minutes until the individual is breathing on their own for at least 15 minutes or until emergency medical services arrive and take over.

Naloxone (brand names: Narcan Nasal, Kloxxado, Zimhi) is a safe and easily accessible medication used to reverse an opioid overdose and help restore breathing by blocking or reversing the opioid effects.

People at risk for an overdose, or their family members or friends, are encouraged to have naloxone on hand in case of an emergency. If possible, have several doses. It is available in pharmacies and can be acquired without a prescription based on state laws. Learn how to use naloxone before it is needed. Ask your pharmacist for more information.

What are the symptoms of a carfentanil overdose?

Symptoms of an opioid overdose may include:

  • breathing that has slowed or stopped (which may lead to death)
  • extreme drowsiness
  • stupor
  • disorientation
  • pinpoint pupils
  • pale and clammy skin
  • vomiting

The onset of these symptoms usually occurs within seconds to minutes of opioid exposure.

Are there other drugs like fentanyl and carfentanil?

Carfentanil is considered one the most potent of the fentanyl analogs. Other powerful fentanyl analogs such as acetyl fentanyl, acryl fentanyl, furanyl fentanyl and ocfentanil are also fully synthesized opioids and considered illegal.

The DEA has identified at least 15 other fentanyl-related opioid compounds. The illicitly manufactured analogs may not be routinely detected in emergency settings because specialized toxicology testing is usually required.

There are other prescription drugs used for pain control in surgery related to legal fentanyl, such as sufentanil and remifentanil (Ultiva). Like fentanyl, they are classified as Schedule II Controlled Substances in the U.S.

For more information, you can contact find evidence-based treatment and service options near you by visiting or by calling the 24/7, National Helpline at 800-662-HELP (4357).

This is not all the information you need to know about carfentanil, fentanyl and naloxone and does not take the place of your healthcare provider's advice. Discuss this information and any questions you have with your doctor or other health care provider.


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