Fentanyl conversion reference
Check OpioidCalc's OME factors by route, then open the formulation-specific pharmacology, cautions and supporting sources.
Educational reference for qualified healthcare professionals. Conversion factors estimate oral morphine equivalent daily dose. They are not a recommended switching dose. Confirm the result with a current source and local guidance.
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Current OpioidCalc factors
Multiply the dose or delivery rate in the stated units by the factor to estimate mg oral morphine equivalent per day. These are the factors currently used by OpioidCalc. Methadone uses 4.7 when converting methadone to OME.
| Route | Input units | OME factor |
|---|---|---|
| Parenteral | mcg/day | 0.2 |
| Transdermal | mcg/hr | 2.4 |
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Formulations and cautions
Choose a formulation to read its pharmacology, population, limitations and source references.
ParenteralDefault in appIntravenous injection
App source review: 27 August 2026
View details and sources
Intravenous injection
App source review: 27 August 2026
View details and sources- Onset
- Almost immediate
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing informationClinical Pharmacology. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Duration
- 30 to 60 minutes after doses up to 100 micrograms
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing informationClinical Pharmacology. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Elimination half-life
- Terminal elimination half-life approximately 219 minutes
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.3 Pharmacokinetics. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Receptor activity
- Full mu-opioid receptor agonist.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.1 Mechanism of Action. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Metabolism
- Fentanyl is metabolised mainly in the liver.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.3 Pharmacokinetics. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Active metabolites
- No analgesically active metabolite is identified by the label.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.3 Pharmacokinetics. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Elimination
- About 75% is excreted in urine, mainly as metabolites; less than 10% is unchanged and about 9% is excreted in faeces.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.3 Pharmacokinetics. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
ParenteralIntramuscular injection
App source review: 27 August 2026
View details and sources
Intramuscular injection
App source review: 27 August 2026
View details and sources- Onset
- 7 to 8 minutes
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing informationClinical Pharmacology. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Duration
- 1 to 2 hours
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing informationClinical Pharmacology. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Elimination half-life
- Terminal elimination half-life approximately 219 minutes
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.3 Pharmacokinetics. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Receptor activity
- Full mu-opioid receptor agonist.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.1 Mechanism of Action. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Metabolism
- Fentanyl is metabolised mainly in the liver.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.3 Pharmacokinetics. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Active metabolites
- No analgesically active metabolite is identified by the label.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.3 Pharmacokinetics. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
- Elimination
- About 75% is excreted in urine, mainly as metabolites; less than 10% is unchanged and about 9% is excreted in faeces.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl citrate injection prescribing information12.3 Pharmacokinetics. United States. Source revised 23 December 2025. App review 27 August 2026. Regulatory product information.
ParenteralContinuous parenteral infusion
App source review: 27 August 2026
View details and sources
Continuous parenteral infusion
App source review: 27 August 2026
View details and sourcesTransdermalDefault in app72-hour transdermal patch
App source review: 27 August 2026
View details and sources
72-hour transdermal patch
App source review: 27 August 2026
View details and sources- Onset
- Serum concentrations generally level off between 12 and 24 hours
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Concentration plateau is not identical to analgesic onset.
- Fentanyl transdermal system prescribing information12.3 Pharmacokinetics. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Peak concentration or effect
- 20 to 72 hours
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl transdermal system prescribing information12.3 Pharmacokinetics. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Duration
- Designed for 72-hour drug delivery
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Delivery interval is not a guarantee of effect duration in an individual patient.
- Fentanyl transdermal system prescribing information2 and 12.3. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Steady state
- By the end of the second 72-hour application
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl transdermal system prescribing information12.3 Pharmacokinetics. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Offset after stopping
- After removal, serum concentrations fall about 50% in 20 to 27 hours because absorption continues from the skin depot.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl transdermal system prescribing information12.3 Pharmacokinetics. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Receptor activity
- Full mu-opioid receptor agonist.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl transdermal system prescribing information12.1 Mechanism of Action. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Metabolism
- CYP3A4 metabolism forms mainly inactive norfentanyl.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl transdermal system prescribing information12.3 Pharmacokinetics. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Active metabolites
- Norfentanyl is inactive.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl transdermal system prescribing information12.3 Pharmacokinetics. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Hepatic impairment
- Hepatic impairment can substantially increase fentanyl exposure.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl transdermal system prescribing information8.6 and 12.3. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Population effects
- Older adults may have a longer apparent terminal half-life after patch use.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Product-specific evidence; do not transfer to other formulations.
- Fentanyl transdermal system prescribing information8.5 and 12.3. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
- Formulation behaviour
- Skin depot causes delayed offset; external heat can markedly increase exposure.
Population: Adults described in the cited product information
Applicability: United States
- Limitation: Do not use intravenous fentanyl half-life as the patch half-life.
- Fentanyl transdermal system prescribing information5.3 and 12.3. United States. Source revised 2 March 2026. App review 27 August 2026. Regulatory product information.
Sources used on this page
Other medicine references
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