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Fentanyl vs. Carfentanil | Potency & Side Effects

Peter Manza, PhD profile image
Reviewed By Peter Manza, PhD • Updated Oct 2, 2023 • 9 cited sources

Fentanyl and carfentanil are both synthetic opioids, but they are significantly different from one another. 

Fentanyl is used medically for pain management in humans, but it is also very often produced and sold on the black market. It is one of the largest driving forces in rising rates of overdose death. 

Carfentanil is primarily for veterinary use and rarely encountered illicitly, resulting in fewer overdose cases. 

Both drugs are highly addictive and incredibly dangerous. They can easily cause an overdose characterized by respiratory depression that requires the administration of naloxone (Narcan) for overdose reversal.

The Main Differences Between Fentanyl & Carfentanil

This table breaks down the differences between fentanyl and carfentanil:[1-5]

PotencyVery strong opioid (far stronger than other popular opioids like oxycodone)Even more potent than fentanyl (about 100 times stronger than fentanyl)
AppearanceMostly available in white powder form on the street, but can also be found in other forms, such as patches, pills or nasal sprays that have been diverted from medical useMost often sold on the street as a white powder
CostsUsually sold for about $50–$64 per gram Often sold for around $17–$194 per gram 
UsesUsed in medical settings for pain management and the purposes of anesthesiaPrimarily used in veterinary medicine for sedating large animals, like elephants, during medical procedures or for safe transport 
AccessibilityComparatively more accessible in illegal drug trade due to its wider use and availabilityLess accessible due to strict regulations, limited production and specialized use
Annual deaths64% of overdose deaths involved synthetic opioids, particularly illegally produced fentanyl, between May 2020 and April 2021Deaths caused by the drug increased by 94%, rising from 421 to 815, from the second half of 2016 to the first half of 2017

How Strong Is Fentanyl?

Fentanyl is an incredibly powerful synthetic opioid. Its strength is usually gauged by comparing it to morphine, a commonly utilized opioid for pain management. Fentanyl’s potency surpasses that of morphine by a significant margin. It is estimated to be around 50 to 100 times more potent.[1]

Its high potency means that even minuscule doses of fentanyl are highly impactful when it comes to pain alleviation. It’s also true that very small doses can also be deadly, usually due to the depression of the respiratory system characterized by slowed breathing.[1]

Though medically prescribed fentanyl is closely monitored by prescribing physicians and law enforcement alike, most fentanyl sold on the street is also produced on the street. It is used to amplify the effects of other drugs like heroin, allowing the dealer to provide an intense product at a lower cost. 

Side Effects of Fentanyl

No two people are the same, and those who are used to taking opioids in high doses may experience fewer side effects when taking fentanyl than someone who rarely, if ever, uses opioids of any kind. Still, it is generally not uncommon for people to experience the following side effects when taking fentanyl:[1,6]

  • Nausea and vomiting
  • Constipation
  • Drowsiness and dizziness
  • Headache 
  • Pale skin
  • Itchiness and rash
  • Sweating
  • Dry mouth
  • Weakness and fatigue
  • Hypotension
  • Respiratory depression

How Strong Is Carfentanil?

Carfentanil boasts an even higher potency than fentanyl, which is an immensely powerful synthetic opioid in its own right. 

To compare the drug to morphine, as fentanyl often is, can help to put the power of carfentanil into perspective. It is estimated to be roughly 100 times more potent than fentanyl and potentially up to 10,000 times stronger than morphine, gram for gram.[7]

Carfentanil is not designed for human use, however. It is that strong so it can be effective in sedating animals that are 10 times larger than the largest human. It is only used in a controlled veterinary setting for the purposes of surgery or safe transport. 

As a result, the drug is absolutely unsafe for human use in any context. It is never prescribed or made available to humans legally. 

Additionally, humans who must handle the drug for the purposes of treating animals are encouraged to wear protective gear in order to ensure that they do not accidentally ingest even the smallest amount of the drug. 

Side Effects of Carfentanil

It is highly unlikely that even a person who regularly consumes very high doses of opioids, and has developed a high tolerance to opioids, would be able to take carfentanil without experiencing serious side effects. The most of likely of these side effects include the following:[8] 

  • Respiratory depression, including serious breathing problems
  • Extreme drowsiness
  • Disorientation
  • Sedation and unconsciousness
  • Nausea and vomiting
  • Pinpoint pupils

Does Narcan Work on Fentanyl & Carfentanil Overdoses?

Yes, Narcan (naloxone) is effective in reversing opioid overdoses, including those involving fentanyl and carfentanil despite their potency. Narcan binds to opioid receptors and essentially kicks off any other opioid in the system, stopping the effect of those substances abruptly. 

However, in practice, due to the exceptional potency of carfentanil, multiple doses of Narcan will almost definitely be needed to stop the overdose.[7] In many cases, this may be true of fentanyl overdose as well. 

In cases where an overdose involving fentanyl or carfentanil is suspected, it is of paramount importance to immediately contact emergency services. Administer naloxone if it’s available, and be ready to give multiple doses.[9]

What to Do in Case of an Overdose

If you suspect someone might be overdosing on an opioid like carfentanil, here is what you should do:[8]

  • Call 911. Stay on the line with the dispatcher, and answer all questions fully and calmly.
  • Stay close and watch the person carefully. If they’re awake, keep talking to them. Otherwise, check to see if their breathing and that their heartbeat is normal.
  • If available, administer naloxone to try to reverse the overdose effects quickly and safely.
  • If the person is breathing but unresponsive, lay them on their side to prevent fluid buildup from affecting breathing. This will also help protect them against possible aspiration if they vomit.
  • If they’re no longer breathing and you know CPR, administer it until an ambulance arrives.

Staying calm and getting help quickly are critical elements to survival in these circumstances. Try not to panic, and ask the 911 dispatcher for next steps if you are unsure of what to do.

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. Fentanyl (trade names: Actiq®, FentoraTM, Duragesic®). Drug Enforcement Administration. Published January 2023. Accessed August 24, 2023.
  2. How much fentanyl is available on the darknet? Australian Institute of Criminology. Published March 2019. Accessed August 24, 2023.
  3. PubChem compound summary for CID 62156, Carfentanil. National Center for Biotechnology Information. Accessed August 24, 2023.
  4. O’Donnell J, Tanz LJ, Gladden RM, Davis NL, Bitting J. Trends in and characteristics of drug overdose deaths involving illicitly manufactured fentanyls — United States, 2019 – 2020. Morbidity and Mortality Weekly Report. 2021;70:1740-1746.
  5. O’Donnell J, Gladden RM, Mattson CL, Kariisa M. Notes from the field: Overdose deaths with carfentanil and other fentanyl analogs detected — 10 States, July 2016–June 2017. Morbidity and Mortality Weekly Report. 2018;67:767–768.
  6. Fentanyl. Healthdirect. Published May 2023. Accessed August 24, 2023.
  7. Carfentanil safety for responders. Indiana Department of Homeland Security. Accessed August 24, 2023.
  8. Carfentanil. Department of Justice. Accessed August 24, 2023.
  9. Carpenter J, Murray BP, Atti S, Moran TP, Yancey A, Morgan B. Naloxone Dosing After Opioid Overdose in the Era of Illicitly Manufactured Fentanyl. J Med Toxicol. 2020;16(1):41-48. doi:10.1007/s13181-019-00735-w

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