[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/) › Fentanyl

[Pharmacology](https://durgical.com/en/pharmacology/) · [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/)

# Fentanyl

A very potent, fast synthetic opioid, key in anesthesia and cancer pain. Illegally made fentanyl drives a severe overdose crisis.

Updated 2026-11-01

- Class: [Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/)
- Receptor: μ-opioid receptor
- ATC code: N02AB03
- WHO Model List of Essential Medicines

◎**μ-opioid receptor**Fentanyl

ⓘ The figure shows fentanyl in the μ receptor bound to its Gi protein; the viewer crops the image to the receptor.

**Target in 3D:** μ-opioid receptor. PDB structure 8EF5 (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/8EF5) · Drag to rotate · pinch to zoom

## Mechanism of action

Fentanyl, a synthetic phenylpiperidine, is a full μ-receptor agonist 50 to 100 times more potent than morphine. It is highly lipid soluble and acts almost at once intravenously. After a single dose it redistributes to muscle and fat, so its effect is short; with continued use it accumulates in those tissues.

- Highly lipid soluble: acts almost at once intravenously
- Potently activates the μ receptor and its Gi protein
- Blocks pain transmission: strong, fast analgesia
- In excess it shuts down the breathing center; naloxone reverses it

## Pharmacokinetics

**Absorption**
Used intravenously, transdermally (patch), transmucosally and intranasally.

**Distribution**
Highly lipid soluble; redistributes to and accumulates in fat and muscle.

**Metabolism**
Liver, mainly by CYP3A4, to norfentanyl and other inactive metabolites.

**Elimination**
Kidney, as metabolites.

**Half-life**
About 3 to 7 hours after an intravenous dose; after patch removal, levels fall more slowly.

**Onset and duration**
Almost immediate intravenously; with the patch, levels rise over 12 to 24 hours.

## Indications

- Analgesia during general anesthesia and surgery
- Analgesia and sedation in intensive care
- Chronic cancer pain in patients already opioid tolerant (patch)

## Adverse effects

### Common

- Nausea and vomiting
- Drowsiness
- Constipation
- Bradycardia
- Miosis

### Serious (rare, important)

- Respiratory depression and apnea
- Muscle rigidity, especially of the respiratory muscles
- Overdose from illegal fentanyl, often mixed unknowingly into other drugs
- Serotonin syndrome with serotonergic drugs

## Contraindications

- Patch in opioid-naive patients or for acute pain
- Significant respiratory depression without monitoring or support
- Paralytic ileus

## Key interactions

**CYP3A4 inhibitors (ritonavir, erythromycin, ketoconazole, grapefruit juice)**
Raise levels and the risk of respiratory depression.

**Benzodiazepines, alcohol and other CNS depressants**
Add sedation and respiratory depression.

**SSRIs, monoamine oxidase inhibitors and other serotonergic drugs**
Risk of serotonin syndrome.

**Heat on the patch (fever, electric blankets)**
Increases drug release and can cause overdose.

## What is monitored

- Respiratory rate, oxygen saturation and sedation
- Blood pressure and heart rate in the operating room

## Memory aid

Fentanyl is a greasy lightning bolt: it strikes the brain in a flash, hides in fat and, if it piles up, strikes again.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does a single intravenous dose of fentanyl wear off quickly even though its half-life is hours?

It redistributes rapidly from the brain to fat and muscle. With continued use those stores fill up and release the drug slowly.

## Which muscular adverse effect of fentanyl can make ventilation hard during anesthesia?

Muscle rigidity, especially of the respiratory muscles.

## Why are CYP3A4 inhibitors dangerous in a patient with a fentanyl patch?

Fentanyl is cleared mainly by CYP3A4; inhibiting it raises fentanyl levels and the risk of respiratory depression.

## Which antidote reverses a fentanyl overdose, and what may it require?

Naloxone. Because fentanyl is so potent, repeated doses may be needed, and the patient must be watched in case respiratory depression returns.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/pharmacology/fentanyl/)

## Related drugs

- [Morphine](https://durgical.com/en/pharmacology/morphine/)
- [Naloxone](https://durgical.com/en/pharmacology/naloxone/)

[← Back to the class: Opioids and antagonists](https://durgical.com/en/pharmacology/classes/opioids-and-antagonists/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Fentanyl | Overdose Prevention | CDC](https://www.cdc.gov/overdose-prevention/about/fentanyl.html) (Centers for Disease Control and Prevention, 2025); [FENTANYL CITRATE injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=1ed25b2c-334e-4021-ada1-3396f07630dc) (DailyMed (U.S. National Library of Medicine), 2026); [FENTANYL TRANSDERMAL patch, extended release](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=e15a7e9b-8025-49dd-9a6d-bafcccf1959f) (DailyMed (U.S. National Library of Medicine), 2026); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N02AB03) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/pharmacology/fentanyl/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/fentanyl/