Short answer: Fentanyl is a synthetic opioid about 50 times stronger than heroin and 100 times stronger than morphine. Pharmaceutical fentanyl is used in anesthesia and for severe pain in people already tolerant to opioids. Illegally made fentanyl, pressed into fake pills or mixed into other drugs, is the main cause of overdose deaths in the United States.
Key takeaways
- What it is: Fentanyl is a synthetic opioid agonist and a Schedule II controlled substance in the US.
- Main uses: Anesthesia; severe pain in opioid-tolerant patients.
- Timing: effects start in seconds to minutes (illicit); 12 to 24 hours (patch) and last 30 to 90 minutes (injected); 72 hours (patch).
- Most dangerous mix: Benzodiazepines (alprazolam, diazepam, clonazepam), which can cause profound sedation, slowed breathing, coma, death.
- Naloxone: it reverses an overdose (, may need repeat doses).
- Dependence risk: Very high.
- Legal route: only with a prescription from a DEA-registered clinician, filled by a licensed pharmacy.
What is fentanyl?
Pharmaceutical fentanyl is used by injection during surgery and anesthesia, and as a skin patch (Duragesic) for severe, persistent pain in people who are already opioid-tolerant. Fast-acting forms that dissolve in the mouth are approved only for breakthrough cancer pain in opioid-tolerant patients.
Most fentanyl involved in overdoses is not pharmaceutical. It is made illegally, often from precursor chemicals shipped from overseas, and is sold as powder, mixed into heroin, cocaine, or methamphetamine, or pressed into counterfeit pills that look like oxycodone, Xanax, or Adderall.
Quick facts
| Fact | Fentanyl |
|---|---|
| Generic name | Fentanyl citrate |
| Brand names | Duragesic (patch), Actiq, Fentora (for cancer pain), Sublimaze (injection) |
| Drug class | Synthetic opioid agonist |
| US legal status | Schedule II, prescription only; illicit analogues are Schedule I |
| Approved uses | Anesthesia; severe chronic pain and breakthrough cancer pain in opioid-tolerant patients |
| Potency | About 100 times morphine; 2 mg can be lethal for a person without tolerance |
| Onset | Seconds when injected or smoked; 12 to 24 hours for a patch |
| Half-life | 3 to 7 hours (injection); about 20 to 27 hours (patch) |
| Broken down by | Liver enzyme CYP3A4 |
How long does fentanyl last?
- Starts working: Seconds to minutes (illicit); 12 to 24 hours (patch)
- Effects last: 30 to 90 minutes (injected); 72 hours (patch)
- Half-life: 3 to 7 hours (injection); about 20 to 27 hours (patch)
Injected fentanyl has a half-life of 3 to 7 hours, but in people who use it heavily it can be detected in urine for a week or more because it is stored in fat.
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 fentanyl?
The FDA requires boxed warnings, its strongest, on fentanyl products, including:
- Fentanyl exposes users to risks of addiction, misuse, and abuse, which can lead to overdose and death.
- Life-threatening slowed breathing can occur, especially when starting treatment or after a dose increase.
- Accidental ingestion, especially by children, can cause a fatal overdose.
- Use with benzodiazepines or other central nervous system depressants, including alcohol, can cause profound sedation, slowed breathing, coma, and death.
Common side effects include drowsiness, nausea, constipation, confusion, sweating, and skin irritation from patches.
Illicit fentanyl is the most dangerous drug in the US supply. Doses vary widely from pill to pill and batch to batch, so a person cannot know how much they are taking. It is increasingly mixed with xylazine, nitazenes, and sedatives that naloxone does not fully reverse.
Warning: Touching fentanyl powder or being near it does not cause overdose. Overdose happens when it is swallowed, injected, smoked, or snorted. First responders should not delay helping someone out of fear of skin contact.
What should you never mix with fentanyl?
| Combined with | What happens | Label 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 |
| Ritonavir, ketoconazole, clarithromycin, fluconazole | Block CYP3A4 and raise fentanyl levels | Boxed warning; avoid or monitor closely |
| Xylazine (in illicit supply) | Deeper sedation not reversed by naloxone; severe wounds | Give naloxone and call 911 |
| Stimulants (cocaine, methamphetamine) | Overdose when the stimulant wears off; heart strain | Very high risk |
Check any combination with the DoseUses combination checker or ask a pharmacist.
What are the signs of a fentanyl overdose, and what should you do?
Fentanyl overdose can happen within seconds to minutes. Signs include pinpoint pupils, sudden unresponsiveness, slow, shallow, or stopped breathing, choking or gurgling, a stiff chest that makes breathing hard, and blue or gray lips and nails.
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 fentanyl 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 fentanyl withdrawal like, and how long does it last?
People who take fentanyl regularly for more than a few weeks become physically dependent, even when they take it exactly as prescribed. Dependence is not the same as addiction, but it means stopping suddenly causes withdrawal.
- 4 to 12 hoursEarly symptomsAnxiety, restlessness, yawning, sweating, runny nose, watery eyes, and muscle aches.
- Days 1 to 3Peak withdrawalDiarrhea, stomach cramps, nausea and vomiting, goosebumps, dilated pupils, fast heartbeat, and strong cravings. Rarely dangerous in healthy adults, but dehydration can be serious.
- Days 5 to 10, then weeksLingering symptomsPoor sleep, low mood, low energy, and cravings can continue for weeks. Tolerance falls quickly, which raises the risk of overdose if use restarts.
See the withdrawal timelines and the full fentanyl withdrawal guide.
Is fentanyl legal?
In the United States, fentanyl is a Schedule II controlled substance. The only legal way to get it is with a prescription from a clinician registered with the Drug Enforcement Administration (DEA), filled by a licensed pharmacy. Depending on state law, that can be a physician, nurse practitioner, or physician assistant.
- Refills: Schedule II prescriptions cannot be refilled. A prescriber can write several prescriptions at once, with dates when each may be filled, for up to a 90-day supply in total.
- Telehealth: federal flexibilities let DEA-registered clinicians prescribe Schedule II to V medicines after a telemedicine visit, without a prior in-person exam, through December 31, 2026. A permanent DEA rule was under final review in late 2026. State rules can be stricter.
- Monitoring: prescribers and pharmacists in most states check a prescription drug monitoring program, a database of controlled-substance prescriptions, before prescribing or dispensing.
Outside the United States
| Country | Status |
|---|---|
| United Kingdom | Class A; prescription only |
| Canada | Schedule I of the Controlled Drugs and Substances Act; prescription only |
| Australia | Schedule 8 controlled drug; prescription only |
| International | Schedule I of the 1961 Single Convention on Narcotic Drugs |
Frequently asked questions about fentanyl
How much fentanyl is lethal?
The DEA estimates that 2 mg, about the amount that fits on the tip of a pencil, can be lethal for a person without opioid tolerance. Illicit pills contain unpredictable amounts.
Does naloxone work on fentanyl?
Yes. Naloxone reverses fentanyl overdose, but more than one dose may be needed. Give a dose, wait 2 to 3 minutes, and repeat if the person is still not breathing normally.
Can you overdose by touching fentanyl?
No. Brief skin contact or being near fentanyl does not cause overdose. Wash hands with soap and water after contact.
What are fentanyl test strips?
Small paper strips that detect fentanyl in a sample of a drug dissolved in water. They are legal in most states and available from many health departments and harm reduction programs.
How long does fentanyl stay in your system?
Injected fentanyl has a half-life of 3 to 7 hours, but in people who use it heavily it can be detected in urine for a week or more because it is stored in fat.
Why is fentanyl in fake pills?
It is cheap to make and very potent, so small amounts can be pressed into pills made to look like real medicines. There is no way to tell by appearance.
Sources
- Duragesic (fentanyl) prescribing information, DailyMed, US National Library of Medicine.
- Fentanyl DrugFacts, National Institute on Drug Abuse.
- One Pill Can Kill, US Drug Enforcement Administration.
- Information about naloxone and nalmefene, US Food and Drug Administration.
- CDC Clinical Practice Guideline for Prescribing Opioids for Pain, 2022, Centers for Disease Control and Prevention, MMWR.
- FindTreatment.gov, Substance Abuse and Mental Health Services Administration.
- Controlled Substance Schedules, DEA Diversion Control Division.
- 21 CFR 1306.12, Refilling prescriptions; issuance of multiple prescriptions (Schedule II), Electronic Code of Federal Regulations.
This guide summarizes the sourced DoseUses Fentanyl profile, written from FDA labels, DEA rules, and federal health agencies. It is educational and is not medical advice. Last updated October 5, 2026.
