Short answer: Carfentanil is a synthetic opioid about 100 times more potent than fentanyl and 10,000 times more potent than morphine. It was developed to sedate elephants and other very large animals and has never been approved for people. Deaths involving carfentanil rose about sevenfold in early 2024.
Key takeaways
- What it is: Carfentanil is a synthetic opioid agonist (fentanyl analog) and a Schedule II controlled substance in the US.
- Medical use: None in humans (veterinary use only).
- Timing: effects start in seconds to minutes and last hours.
- Most dangerous mix: Benzodiazepines (alprazolam, diazepam, clonazepam), which can cause profound sedation, slowed breathing, coma, death.
- Naloxone: it reverses an overdose (several doses may be needed).
- Dependence risk: Very high.
- Legal route: no approved US product for personal use; possession without a prescription is a crime.
What is carfentanil?
Carfentanil was synthesized in 1974 and marketed as Wildnil to immobilize animals such as elephants and moose. It has no approved medical use in people.
Carfentanil causes the same effects as other opioids, sedation, euphoria, and slowed breathing, but at microgram doses. The amount in a single grain can be enough to stop breathing in someone without tolerance.
Quick facts
| Fact | Carfentanil |
|---|---|
| Drug class | Synthetic opioid agonist; fentanyl analog |
| US legal status | Schedule II (no approved human use) |
| Approved uses | Veterinary immobilization of large animals only |
| Potency | About 100 times fentanyl and 10,000 times morphine |
| How it appears | Mixed into counterfeit pills, heroin, and fentanyl powder |
| Lethal amount | Around 2 mg, or less, can be fatal |
| Reversal agent | Naloxone; multiple doses are often needed |
How long does carfentanil last?
- Starts working: Seconds to minutes
- Effects last: Hours
Timing varies with the dose, the form, how it is taken, liver and kidney function, age, and other drugs taken at the same time.
What are the biggest risks of carfentanil?
Overdose: breathing can stop within minutes. Even people with high fentanyl tolerance can overdose.
Naloxone resistance: carfentanil binds tightly to opioid receptors, so overdoses often need more than one dose of naloxone, and breathing can slow again as naloxone wears off.
Unknown dose: because it is mixed unevenly into other drugs, two pills or bags from the same batch can contain very different amounts.
Warning: Fentanyl test strips may not reliably detect carfentanil. Never use alone, carry naloxone, and call 911 for anyone who is hard to wake.
What should you never mix with carfentanil?
| Combined with | What happens | Guidance |
|---|---|---|
| Benzodiazepines (alprazolam, diazepam, clonazepam) | Profound sedation, slowed breathing, coma, death | Boxed warning; avoid unless no alternative |
| Alcohol | Stronger sedation and slowed breathing | Avoid |
| Gabapentin, pregabalin, sleep medicines, muscle relaxants | Additive sedation and breathing problems | Use caution; lower doses |
| Stimulants (cocaine, methamphetamine) | Masked sedation; overdose when the stimulant wears off | Dangerous |
| Xylazine or medetomidine | Deeper, longer sedation not reversed by naloxone | Dangerous |
Check any combination with the DoseUses combination checker or ask a pharmacist.
What are the signs of a carfentanil overdose, and what should you do?
Carfentanil overdose causes pinpoint pupils, unresponsiveness, blue or gray lips, and slow or stopped breathing, often within minutes. Brief skin contact is very unlikely to cause an overdose, but responders should avoid handling powders without gloves.
If someone may have overdosed
- Call 911 if the person is unresponsive, cannot be woken, has blue or gray lips, or is breathing slowly or not at all.
- Give naloxone (Narcan or a generic nasal spray, sold without a prescription) into one nostril. If there is no response after 2 to 3 minutes, give another dose.
- If you are trained, give rescue breaths. Otherwise place the person on their side so they do not choke.
- Stay with them. Naloxone can wear off before carfentanil does, so the overdose can return even after the person wakes up.
- Most states have Good Samaritan laws that protect people who call 911 for an overdose from some drug charges.
What is carfentanil withdrawal like, and how long does it last?
People exposed regularly to carfentanil through the drug supply develop opioid dependence and withdrawal similar to fentanyl.
- 4 to 12 hoursEarly symptomsAnxiety, restlessness, yawning, sweating, runny nose, watery eyes, and muscle aches.
- Days 1 to 3Peak withdrawalDiarrhea, cramps, vomiting, goosebumps, fast heartbeat, and strong cravings.
- Days 5 to 10, then weeksLingering symptomsPoor sleep, low mood, and cravings. Tolerance falls quickly.
See the withdrawal timelines and the full carfentanil withdrawal guide.
Is carfentanil legal?
Carfentanil is a Schedule II controlled substance because of its approved veterinary use. Possessing or selling it outside DEA-registered veterinary or research settings is a federal crime.
- Possession: under federal law, a first conviction for possessing any controlled substance without a valid prescription can bring up to one year in prison and a minimum fine of $1,000. Penalties rise with prior convictions.
- Trafficking: trafficking fentanyl analogs carries mandatory minimum sentences, and distribution resulting in death or serious injury carries 20 years to life.
Outside the United States
| Country | Status |
|---|---|
| United Kingdom | Class A |
| Canada | Schedule I of the Controlled Drugs and Substances Act |
| China | Controlled since March 2017 |
| International | Schedules I and IV of the 1961 Single Convention (since 2018) |
Frequently asked questions about carfentanil
How strong is carfentanil?
About 100 times stronger than fentanyl and 10,000 times stronger than morphine.
Does naloxone work on carfentanil?
Yes, but several doses are often needed, and the person must be watched because the overdose can return.
Can you overdose by touching carfentanil?
Brief skin contact is very unlikely to cause an overdose, but powders should not be handled without gloves, and should not be inhaled.
Is carfentanil used in medicine?
Only in veterinary practice, to sedate very large animals. It has never been approved for people.
Is carfentanil back in the drug supply?
Yes. Deaths involving carfentanil rose about sevenfold between early 2023 and early 2024.
Sources
- Detection of Illegally Manufactured Fentanyls and Carfentanil in Drug Overdose Deaths, United States, 2021 to 2024, Centers for Disease Control and Prevention, MMWR, December 2024.
- One Pill Can Kill, US Drug Enforcement Administration.
- Information about naloxone and nalmefene, US Food and Drug Administration.
- Controlled Substance Schedules, DEA Diversion Control Division.
- 21 U.S.C. 844, Penalties for simple possession, Legal Information Institute, Cornell Law School.
- 21 U.S.C. 841, Prohibited acts A (trafficking penalties), Legal Information Institute, Cornell Law School.
- National Helpline, Substance Abuse and Mental Health Services Administration.
- FindTreatment.gov, Substance Abuse and Mental Health Services Administration.
This guide summarizes the sourced DoseUses Carfentanil profile, written from FDA labels, DEA rules, and federal health agencies. It is educational and is not medical advice. Last updated October 5, 2026.
