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What Is Carfentanil? A Lethal Opioid Sold as Heroin

July 2, 2022

Table of Contents

Carfentanil is the most potent fentanyl analog, and the drug has been reported in an alarming number of human overdose deaths in some U.S. states. This illegally manufactured substance is often mixed with heroin to increase its potency. As a result, buyers may not know exactly what they are ingesting.

What Is Carfentanil?

Carfentanil is one of many fentanyl analogs which are similar in chemical structure to fentanyl. However, it is not routinely detected because specialized toxicology testing is required.

Like fentanyl, carfentanil is a synthetic narcotic analgesic produced from morphine. While fentanyl is about 100 times more powerful than morphine, carfentanil is 100 times more potent than fentanyl. In other words, carfentanil is 10,000 times more potent than morphine.[1]

Strength of Heroin vs Morphine vs Carfentanil

Carfentanil is not approved for use in humans in any capacity. It is typically found in veterinary medicine to sedate large animals, primarily elephants. In fact, the drug is so powerful that veterinarians use protective gear when handling it so they don’t breathe it in or absorb it through their skin.

The drug can be purchased online or on the streets. Common street names of carfentanil include “drop dead”, “C.50”, “serial killer”, and when mixed in combination with other opioid/opioid-like drugs, “grey death”. 

Carfentanil is often used as a cutting agent in other drugs like heroin and fentanyl, increasing the risks of overdose and other complications.

How to Recognize Carfentanil?

Non-medical, fully synthesized and illegal fentanyl analogs that are chemically similar to fentanyl include:

  • Acetylfentanyl
  • Furanylfentanyl
  • Ocfentanil
  • Carfentanil 

In addition, the Drug Enforcement Agency (DEA) has identified at least 15 other related compounds, including new ones like U-47700.

Street carfentanil first appeared in the early 2000s, and there has been an escalation in cases since 2016. The substance has been identified in powder, tablet, or capsule formulations as well as in liquid form and on blotter paper.[2] Thus, it can be pharmacologically active via multiple routes of administration, including orally, intranasally, subcutaneously, intravenously, and intramuscularly. 

Carfentanil can also be absorbed through the skin or accidental inhalation of airborne powder.

How Does Carfentanil Affect Humans?

Carfentanil rapidly binds to opioid receptors in the brain, overwhelming neural chemistry and leading to overdose symptoms almost immediately.

For comparison, fentanyl creates an intense euphoria and drowsiness when binding to the opioid receptors in the brain. These sensations are caused by elevated dopamine levels and a reduced ability for the opioid receptors to absorb this neurotransmitter due to the presence of the narcotic. 

These receptors also control breathing rate, which is why opioid overdoses are typically characterized by depressed, irregular, or stopped breathing. Similar to other opioid agonists, carfentanil depresses the respiratory center, suppresses the cough reflex, and causes pupil constriction. 

Carfentanil Side Effects

Carfentanil induces side effects such as drowsiness and sedation.[3] Major symptoms also include[2]:

  • Sudden drowsiness
  • Slowed or depressed breathing
  • Disorientation
  • Sedation
  • Pinpoint pupils
  • Clammy skin
  • Death

Carfentanil Overdose

Because a tiny, almost invisible amount (e.g., 2 mg dosage) of carfentanil is deadly to a human, the primary medical effect of the substance is overdose and death. 

Survival is possible only when multiple doses or continuous infusions of the opioid antidote naloxone (Narcan) are administered soon after carfentanil use. In many cases, such treatment is not successful.

Deaths from carfentanil increased 94% during the first half of 2017 and then appeared to dip in 2018.[4] This is possibly due to China adding carfentanil to its list of controlled substances in 2017, which resulted in a drying up of the U.S. supply. 

In addition, overdose deaths from two other fentanyl analogs — acrylfentanyl and furanylfentanyl — started surging at about that time. Preliminary data points to an accelerating and staggering (30% in the year ended February 2021) rate of increase in overdose deaths from drugs in the U.S.[5] 

While carfentanil’s contribution to that growth rate has yet to be determined, it is likely that every fentanyl analog has played a role in the surge.

Is Carfentanil Addictive?

Reports from the U.S. Department of Justice (DOJ) and the DEA point to the reality that people are using and possibly abusing carfentanil, whether knowingly or not.[2,6] 

Canadian health authorities have also sounded the alarm about illicit distribution, use and overdose deaths from carfentanil. Many reports of illicit carfentanil seizures have appeared around the world over the past few years.[7] 

However, we cannot speculate on “how addictive” the drug is. There are four main reasons why this is the case:

  1. The abuse potential of carfentanil has not been tested in controlled studies in either preclinical or clinical research.
  2. Controlled pharmacology data on the dependence or tolerance potential of carfentanil in non-human species and humans are unavailable. 
  3. The potency of illicitly manufactured fentanyl analogs has not been evaluated in humans.
  4. The lethal dose range for carfentanil in humans is unknown. 

Carfentanil is not mentioned in SAMHSA’s 2015 National Survey on Drug Use and Health (NSDUH), and the 2017 Global Drug Survey provides no information on the prevalence of use. 

What we do know is that the overdose rate with carfentanil is sky-high. In all likelihood, few individuals remain addicted to the substance for long, because before long they are deceased from overdosing on it. 

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Photo: DEA

Lane McKenna

Lane McKenna has been a health and wellness writer for over 20 years. After graduating from Brown University (AB English), Lane spent over a decade on Wall Street West as a leading health services securities analyst. Opioid use disorder has long been one of her areas of expertise.

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1. Suzuki J, El-Haddad S. A review: fentanyl and non-pharmaceutical fentanyls. Drug Alcohol Depend 2017;171:107–16.

2. DEA Issues Carfentanil Warning to Police and the Public. United States Drug Enforcement Administration. 2017.

3. Carfentanil: Critical Review Report. World Health Organization. November 2017.

4. O’Donnell JK, Halpin J, Mattson CL, Goldberger BA, Gladden RM. Deaths Involving Fentanyl, Fentanyl Analogs, and U-47700 — 10 States, July–December 2016. MMWR Morb Mortal Wkly Rep 2017;66:1197–1202.

5. Ahmad FB, Rossen LM, Sutton P. Provisional drug overdose death counts. National Center for Health Statistics. 2021.

6. Officer Safety Alert. U.S. Department of Justice.

7. Carfentanil - Backgrounder. Alberta Health Services. February 2018.

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