Also known as

W-18, widnil (the brand name), R-33799


Psychoactive [1].


Carfentanil is an opioid that is used by veterinarians for very large animals like elephants. It is not for human use. It is approximately 100 times more toxic than fentanyl and 10,000 times more toxic than morphine. This means carfentanil can be deadly in extremely small amounts [2]. It is easily absorbed through the skin, as well as inhaled, posing a huge risk to anyone who might accidentally come into contact with it. A tiny dose (equivalent to a few grains of table salt) can prove lethal [3].

Medical usage

There is no proven medical use in humans [4].

What does it look like?

Law enforcement and emergency medical personnel warn that carfentanil sold illicitly looks like other drugs found on the street, including cocaine and heroin, because it is an odorless, white powder. Carfentanil, like fentanyl, has been found cutting heroin in order to increase its potency and the heroin dealer’s supply of the substance [5].

Carfentanil base is a white powder and has also been identified in seized white, pink, and brown powders along with other substances. Carfentanil citrate is highly water soluble with no distinguishing odour [4].


Most of fentanyl analogues including carfentanil are usually manufactured in China and exported from there to all over the world. In October 2016, Associated Press news reported finding 12 Chinese laboratories willing to export carfentanil to the United States, Canada, the United Kingdom, France, Germany, Belgium, and Australia for the price of US$2750/kg. Until March of 2017, carfentanil was not regulated in China; it was openly and legally manufactured and sold by Chinese companies. The drug can be also found easily online, on the darknet, through related websites in which it is often labeled as a research chemical and sold through direct mail shipments in prices from US$800 to 2500 per gram. More specifically in 2016, one darknet search engine gave 118 websites selling carfentanil. Because carfentanil is more potent than heroin, its trafficking quantities are significantly less than those of heroin. Therefore, it is easier and cheaper to be smuggled without necessarily being cheap to manufacture [4].


The National Crime Agency in the UK has issued a warning to drug users that fentanyl and carfentanil have been detected in heroin in North-East England. The drugs have been implicated in recent deaths in Yorkshire, Cleveland and Humber [3].

Carfentanil has been characterised as the most potent, dangerous, and commercially available fentanyl analogue. It has been also used as a chemical weapon, making it a very serious hazard to public safety. It has been reported through seizures, intoxication cases, and illicit drug trafficking in Europe, Asia, the USA, and Australia [4].

What are the different forms?

It is exported from China in a powdered and tablet form, but it also comes in many other forms such as blotter papers, patches, and sprays [4].


Carfentanil acts primarily on the mu (some kappa and delta) opioid receptors as an agonist. It will induce similar effects of analgesia as other opioids, however, due to its potency, it will also induce strong side effects such as sedation. Consequently, that is why it is used as a tranquillizer for large animals. Carfentanil interacts predominately with the opioid mu-receptor. These mu-binding sites are discretely distributed in the brain, spinal cord, and other tissues. It exerts its principal pharmacologic effects on the central nervous system. Its primary actions of therapeutic value are analgesia and sedation. Carfentanil also depresses the respiratory centres, the cough reflex, and constricts the pupils [6].


In some cases, it has been accidentally absorbed through the skin, inhaled, or ingested [4].


Carfentanil's plasma half-life was calculated and found to be 51.4 (±16.2) and 41.8 (±17.5) minutes for cocaine users and non-drug using controls, respectively. As there were not any significant differences in its half-life among the two groups, they concluded that these differences are most likely pharmacodynamically based [4].


Because of carfentanil's potency, the effects on the human body and brain are very rapid [5].

Carfentanil rapidly binds to opioid receptors in the brain, overwhelming neural chemistry and leading to overdose symptoms almost immediately. 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 [5].


Exposure to carfentanil produces signs and symptoms very similar to those of opioid toxicity and overdose -

  • pinpoint (constricted) pupils,
  • dizziness, lethargy, sedation,
  • shallow breathing (respiratory depression),
  • loss of consciousness,
  • nausea, vomiting,
  • heart failure, weak or absent pulse,
  • cold, clammy skin,
  • cardiac arrest,
  • death [3].


The Drug Enforcement Administration issued a warning in September 2016 about carfentanil, which included a disclaimer that overdose symptoms could begin within minutes of exposure to the powerful narcotic [5]>. The DEA warned that a person experiencing these symptoms should seek immediate medical attention -

  • sudden drowsiness,
  • slowed or depressed breathing,
  • disorientation,
  • sedation,
  • pinpoint pupils,
  • clammy skin [5].

Because these symptoms can appear very shortly after exposure to carfentanil, the DEA recommended that a dose of naloxone be immediately administered in order to slow down the overdose long enough for emergency medical services to arrive and treat the individual [5].

Signs of intoxication

  • cold and clammy skin,
  • nausea,
  • vomiting,
  • pinpoint pupils,
  • disorientation,
  • dizziness,
  • lethargy,
  • sedation,
  • sudden drowsiness,
  • respiratory disorders,
  • possible heart failure, and
  • weak pulse [4].

The DEA advised that anyone experiencing any of the mentioned symptoms should immediately seek medical care. The mentioned symptoms are dose dependent. High doses can lead to severe intoxications and consequently to death [4].


It is approximately 100 times more toxic than fentanyl and 10,000 times more toxic than morphine. This means carfentanil can be deadly in extremely small amounts [2].


Carfentanil is being cut in to other illicit drugs like heroin and counterfeit pills made to look like prescription opiods (including green pills stamped 'CDN' on one side and '80' on the other). There is no easy way to know if carfentanil is in your drugs, you can't see it, smell it or taste it. It is extremely toxic and a very small amount can cause an overdose, or even death [2].


Carfentanil is one of the most dangerous fentanyl analogues to come into the drug market in recent years. As a result, there is an undeniable need for the safety of the public for it to be regulated in order to minimize the potential of an imminent health hazard as much as possible. The drug is not scheduled as of now under the 1961 United Nations Convention, but it is a controlled substance in many countries in Europe, as well as the United States, Canada, Australia, and China.

In Czech Republic, carfentanil is regulated under the Government regulation concerning lists of drugs issued on December 18, 2013. Carfentanil was included in Annex 1 of Danish Executive Order Number 557 of 31 May 2011, which came in force on November 24, 2016; the drug was included on the B List, and it can be used only for medical and scientific purposes. In the United Kingdom carfentanil is controlled under the Misuse of Drugs Act 1971.

In the United States, the DEA classifies carfentanil as a Schedule II substance according to the Federal Controlled Substances Act issued on October 28, 1988. On September 29, 2016 the Department of Health in Pennsylvania issued the placement of carfentanil in Schedule II under the Controlled Substance, Drug, Device, and Cosmetic Act.

In Canada, carfentanil is a Schedule I substance under Canada's Controlled Drugs and Substances Act, which was last amended on May 18, 2017.

In Australia, carfentanil has been included in the Poisons Standard in June 2017, by the Australian Department of Health. It has been clarified as a schedule 8 poison, and legal restrictions apply to its manufacture, supply, distribution, possession, and any type of abuse, physiological misuse, or physical dependence.

China started to discuss scheduling carfentanil 4 months after the Associated Press discovered 12 Chinese laboratories willing to export carfentanil to the United States, Canada, and Europe in October 2016. The scheduling came into force in March 2017 when it was added to the list regulated by the "Administrative Measures on Narcotics and Psychotropic Substances without Medical Use" [4].

Legal Status

Class A [1].

What if you're caught?

  • Penalty for possession - Up to seven years in prison and/or an unlimited fine.
  • Penalty for dealing - Up to life in prison and/or an unlimited fine [1].

Mixing with other drugs

Carfentanil is often used to adulterate heroin, cocaine, and fentanyl. In some other cases, it is labeled and sold as heroin. In Cincinnati, OH, a new drug appeared in 2016 under the street name of gray death. It looks like cement and often contains cocaine, heroin, fentanyl, carfentanil, furanylfentanyl, and acrylfentanyl. Carfentanil has also been identified in mixtures along with caffeine, antihistamines, furanylfentanyl, or acrylfentanyl, while in some other cases it has been found to be laced with ketamine. Unconfirmed reports of marijuana laced with carfentanil have been found in northeast Ohio and Canada. Furthermore, the drug has been found in counterfeit pills. The DEA reported that carfentanil had shown up in counterfeit prescription pills sold as OxyContin and Xanax [4].


Carfentanil is the most potent of the commercially available fentanyl analogues. It was synthesised in 1974 by a group of chemists at Janssen Pharmaceuticals, and since then it has been used in veterinary medicine as a tranquillizer for the sedation of large animals. Carfentanil has been pharmacologically studied mostly in animals, but also in humans. Some evidence suggests that it has been used as a chemical weapon by the Russian military, while attempting to subdue a terrorist siege of the Moscow Theatre [4].


  1. 1.0 1.1 1.2 wedinos, Carfentanil, 2018,
  2. 2.0 2.1 2.2 Ottawa Public Health, Fentanyl and Carfentanil, 2018,
  3. 3.0 3.1 3.2 Castle Craig Hospital Ltd, Carfentanil, 2018,
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 Misailidi, N. and Papoutsis, I. and Panagiota, N. and Artemisia, D. and Spiliopoulou, C. and Athanaselis, S., Fentanyls continue to replace heroin in the drug arena: the cases of ocfentanil and carfentanil, Forensic Toxicology, 2018, 36, 11, 12-32, ISSN 1860-8965,,
  5. 5.0 5.1 5.2 5.3 5.4 5.5 American Addiction Centers, What Is Carfentanil?, 2018,
  6. pubchem, Carfentanil, 2018,