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Carfentanil Hidden Dangers: The Side Effects Guide

Peter Manza, PhD profile image
Reviewed By Peter Manza, PhD • Updated Nov 24, 2023 • 12 cited sources

The main hidden danger of carfentanil is that it is exponentially more dangerous than other synthetic opioids (which are already very dangerous), such as fentanyl. Fatal overdose is highly likely with carfentanil use, whether it is taken intentionally or laced into other drugs.[1]

What Is Carfentanil?

Carfentanil is an extremely strong synthetic opioid. It is in the fentanyl category of drugs, but it is much stronger than fentanyl — up to 100 times stronger. It is estimated to be 10,000 times stronger than morphine.[1] Even tiny amounts of carfentanil can be fatal, leading to respiratory depression, unconsciousness and death in humans. 

While there is a medical application for carfentanil, it is not intended for human consumption. It was originally developed for veterinary applications as a tranquilizer for large animals, like elephants and rhinoceros.[2] 

However, carfentanil has been found on the black market, often mixed with other illegally traded drugs. It poses severe risks to anyone — users, dealers and first responders — due to its heightened lethality and the inability of standard opioid overdose reversal medications, like naloxone, to counteract its effects. The DEA issued a warning advising people to seek emergency medical attention immediately if they are exposed to carfentanil.[3]

History & Background of Carfentanil

Carfentanil was originally developed in 1974 and then sold in 1986 under the brand name Wildnil. It was exclusively intended for tranquilizing elephants and other large animals for veterinary operations.[2] A 2 ml intramuscular dose of carfentanil is enough to quickly sedate an elephant.[4] 

In veterinary medicine, carfentanil is usually administered with other drugs, like etorphine, to induce a strong sedative effect and functionally immobilize the animal.[5] The method of administration is typically via tranquilizer dart. 

This lets veterinarians and wildlife experts safely perform required procedures, such as medical examinations, blood sampling, transport or surgeries. The sedation induced by carfentanil also keeps the animal safe during the procedures, rendering them unconscious and fully pain-free. The animals are closely monitored during and after their sedation. 

Commercial production of Wildnil was discontinued in 2003. There is currently no FDA-approved version of the drug.[6] 

Carfentanil’s Use Today

Carfentanil is now only available in compounded form, which means that it is made by a pharmacist to order on a case-by-case basis. This means that, even within veterinary medicine, carfentanil is tightly controlled and regulated because of its extreme potency. 

Improper use can endanger both the animal and the humans who have to handle the animal or the carfentanil itself. In order to administer carfentanil, veterinarians and zoologists require specialized training and permits.[2]

Side Effects of Carfentanil

Carfentanil is not meant for human use. Even minute amounts of carfentanil can trigger severe side effects that can become fatal if left unchecked. 

These are potential side effects of carfentanil:[1,7]

Respiratory Depression

As an extremely potent opioid, carfentanil can quickly and dramatically suppress the respiratory system, leading to increasingly shallow breathing to the point of oxygen deprivation, respiratory arrest and death.


Because of how potent it is, there is a significantly high risk of overdose with carfentanil. Signs of an opioid overdose include unconsciousness and drastically reduced heart rate and breathing rate.

Nausea & Vomiting

Carfentanil stimulates the chemoreceptor trigger zone in the brain, leading to nausea and vomiting through central and peripheral mechanisms.

Confusion & Dizziness

Carfentanil depresses the central nervous system, changing balance and coordination, resulting in dizziness due to its sedative effects on the brain.

Cardiac Concerns

Cardiac arrest, irregular heart rhythms and other cardiovascular problems may occur.

Can People Overdose from Carfentanil?

Yes, an overdose is likely if a person takes carfentanil. Due to the drug’s potency, the likelihood that even a small dose will cause a fatal overdose is staggeringly high.

A key factor in the likelihood of overdosing with carfentanil is the rapid onset of its effects. Once in the bloodstream, carfentanil quickly crosses the blood-brain barrier, and the onset of symptoms may occur within a couple of minutes.[9,10] Unless naloxone is immediately on hand, the chance of successfully reversing the overdose drops precipitously. 

Difficulty in Treating Carfentanil Overdose

Even if naloxone can be quickly obtained and administered, the potency of carfentanil is so intense that a single dose of naloxone might not be enough to reverse an overdose. Multiple doses of naloxone will likely be needed to counteract the effects of carfentanil, where a single dose might have sufficed for overdose from a less potent opioid, like heroin.[11]

Carfentanil’s unprecedented potency makes it difficult to measure and handle accurately, which increases the risk of intentional overdose. In addition, carfentanil is frequently laced with other illicit drugs (such as opioids, stimulants or counterfeit prescription medication) to increase either their potency or the profitability of the dealers and suppliers. The unregulated, sometimes random risk of combinations, greatly increases the risk of overdose.[12] 

Finding Treatment for Carfentanil Addiction

If you’ve used carfentanil even once, you’re lucky to be alive, and it’s a clear sign that you need treatment for opioid use disorder (OUD). Medication for Addiction Treatment (MAT) is an evidence-based approach to managing OUD, enabling patients to live in recovery from opioid misuse for the rest of their lives. 

At Bicycle Health, we offer Suboxone in our telehealth MAT program. You can meet with an addiction expert from the comfort of your home, no matter where you live, and your treatment will be fully private and confidential. 

We can often get you a same-day prescription for Suboxone that you can pick up at a pharmacy near you, so you can start your journey to a better life today. Reach out now to learn more.

Reviewed By Peter Manza, PhD

Peter Manza, PhD received his BA in Psychology and Biology from the University of Rochester and his PhD in Integrative Neuroscience at Stony Brook University. He is currently working as a research scientist in Washington, DC. His research focuses on the role ... Read More

  1. Zawilska JB, Kuczyńska K, Kosmal W, Markiewicz K, Adamowicz P. Carfentanil – from an animal anesthetic to a deadly illicit drug. Forensic Science International. 2021;320:110715. 
  2. Carfentanil information. Zoo and Aquarium All Hazards Partnership. Published August 21, 2017. Accessed November 10, 2023.
  3. DEA issues carfentanil warning to police and public. Drug Enforcement Administration. Published September 22, 2016. Accessed November 10, 2023.
  4. Delaware Health Alert #377: Health Update – Carfentanil and fentanyl analogs pose threat to public safety. Division of Public Health, Delaware Health and Social Services, State of Delaware. Published July 13, 2017. Accessed November 10, 2023.
  5. Heard DJ, Nichols WW, Buss D, Kollias GV. Comparative cardiopulmonary effects of intramuscularly administered etorphine and carfentanil in goats. American Journal of Veterinary Research. 1996;57(1):87-96. Accessed November 10, 2023.
  6. Carfentanil linked to 1,200 human deaths. American Veterinary Medical Association. Published October 1, 2018. Accessed November 10, 2023.
  7. Edinoff AN, Martinez Garza D, Vining SP, et al. New synthetic opioids: Clinical considerations and dangers. Pain and Therapy. 2023;12(2):399-421.  
  8. Fomin D, Baranauskaite V, Usaviciene E, et al. Human deaths from drug overdoses with carfentanyl involvement—new rising problem in forensic medicine. Medicine. 2018;97(48):e13449.
  9. Waite K, Deeken A, Perch S, Kohler LJ. Carfentanil and current opioid trends in Summit County, Ohio. Academic Forensic Pathology. 2017;7(4):632-639.
  10. Carfentanil. PubChem. Accessed November 10, 2023.
  11. Moss RB, Carlo DJ. Higher doses of naloxone are needed in the synthetic opioid era. Substance Abuse Treatment, Prevention, and Policy. 2019;14(1). 
  12. Jalal H, Burke DS. Carfentanil and the rise and fall of overdose deaths in the United States. Addiction. Published September 25, 2020. Accessed November 10, 2023.

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