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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Opioid Agonist [EPC]
Fentanyl is a potent synthetic opioid agonist used for the management of severe pain. It belongs to the phenylpiperidine class and is approximately 50 to 100 times more potent than morphine, acting primarily on the mu-opioid receptors in the central nervous system.
Name
Fentanyl
Raw Name
FENTANYL CITRATE
Category
Opioid Agonist [EPC]
Salt Form
Citrate
Drug Count
4
Variant Count
68
Last Verified
February 17, 2026
RxCUI
1735003, 1735007, 1735008, 1735013, 2168270, 2474269, 2629337, 197696, 245134, 245135, 245136, 577057, 1603495, 1603498, 1603501, 1735004, 1735006, 2474267, 310293, 310294, 310295, 310297, 313992, 313993
UNII
MUN5LYG46H, UF599785JZ
About Fentanyl
Fentanyl is a potent synthetic opioid agonist used for the management of severe pain. It belongs to the phenylpiperidine class and is approximately 50 to 100 times more potent than morphine, acting primarily on the mu-opioid receptors in the central nervous system.
Detailed information about Fentanyl
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Fentanyl.
Fentanyl is a highly potent synthetic opioid analgesic (pain reliever) that belongs to the phenylpiperidine class of drugs. It is classified as a Schedule II controlled substance in the United States due to its high potential for abuse and severe physical and psychological dependence. Originally synthesized by Paul Janssen in 1960, Fentanyl was first approved by the FDA in 1968 (as Sublimaze) for use as an intravenous anesthetic. Since then, its clinical utility has expanded into various delivery systems designed to manage chronic, severe pain and breakthrough cancer pain in patients who are already opioid-tolerant. Because Fentanyl is approximately 50 to 100 times more potent than morphine, it is measured in micrograms (mcg) rather than milligrams (mg), making precise dosing and administration critical for patient safety.
Clinically, Fentanyl is used to treat patients with 'breakthrough' cancer pain (sudden flares of pain that occur despite around-the-clock opioid treatment) or for the management of severe, persistent pain that requires continuous, long-term opioid therapy. It is not intended for mild or short-term pain, such as pain from headaches, dental work, or post-operative recovery in patients who are not already taking opioids. Healthcare providers typically reserve Fentanyl for cases where other pain management strategies have proven insufficient.
Fentanyl functions as a full opioid agonist, primarily targeting the mu-opioid receptors (MOR) located throughout the brain, spinal cord, and other tissues in the body. At the molecular level, Fentanyl is highly lipophilic (fat-soluble), which allows it to rapidly cross the blood-brain barrier and produce its effects. When Fentanyl binds to these receptors, it triggers a cascade of intracellular events, including the inhibition of adenylate cyclase and the closing of voltage-gated calcium channels, while simultaneously opening potassium channels. This results in hyperpolarization of the neuron, effectively reducing its excitability and inhibiting the release of neurotransmitters such as substance P, glutamate, and acetylcholine, which are responsible for transmitting pain signals.
Beyond its analgesic properties, Fentanyl's interaction with mu-receptors in the brain's reward system (the mesolimbic pathway) leads to a surge in dopamine, producing the euphoria often associated with opioid use. However, its binding to receptors in the brainstem also suppresses the body's respiratory drive, which is the primary cause of fatal overdose. Because of its high affinity for the mu-receptor, Fentanyl can displace other opioids and requires significant amounts of naloxone (an opioid antagonist) to reverse in emergency situations.
The bioavailability of Fentanyl varies significantly by the route of administration. When administered intravenously, bioavailability is 100%. Transdermal patches (e.g., Duragesic) provide a slow, continuous delivery of the drug through the skin into the systemic circulation, with bioavailability reaching approximately 92%. Transmucosal forms, such as buccal tablets (Fentora) or lozenges (Actiq), bypass first-pass metabolism in the liver by absorbing directly through the oral mucosa, providing a bioavailability of roughly 50% to 65%. Food does not significantly affect the absorption of transmucosal Fentanyl, though it may slightly alter the rate of absorption for buccal tablets.
Fentanyl is highly protein-bound (approximately 80% to 85%), primarily to alpha-1-acid glycoprotein and, to a lesser extent, albumin. Due to its high lipophilicity, it is rapidly distributed to the brain, heart, lungs, and kidneys before being redistributed to slower-perfused tissues like skeletal muscle and fat. This redistribution is responsible for the short duration of action seen after a single intravenous bolus, despite the drug's longer terminal half-life.
Fentanyl is primarily metabolized in the liver and intestinal mucosa via the cytochrome P450 3A4 (CYP3A4) enzyme system. The major metabolic pathway is oxidative N-dealkylation to norfentanyl, which is an inactive metabolite. Because Fentanyl is so heavily dependent on CYP3A4 for clearance, any substance that inhibits or induces this enzyme can dramatically alter Fentanyl concentrations in the blood, leading to either toxicity or lack of efficacy.
Approximately 75% of a Fentanyl dose is excreted in the urine, mostly as metabolites, with less than 10% excreted as unchanged drug. About 9% of the dose is found in the feces. The elimination half-life varies by product: it is approximately 3–7 hours for intravenous use, but can be 20–27 hours for transdermal patches due to the continued absorption from the skin depot even after the patch is removed.
Fentanyl is FDA-approved for several specific indications:
Off-label uses may include the management of severe acute pain in emergency department settings or for sedation in mechanically ventilated patients in the intensive care unit (ICU), though these uses are strictly monitored by medical professionals.
Fentanyl is available in several specialized delivery systems:
> Important: Only your healthcare provider can determine if Fentanyl is right for your specific condition. Due to the risk of fatal respiratory depression, it must only be used by patients who are already habituated to potent opioids.
Dosage for Fentanyl is highly individualized and depends on the patient's prior opioid exposure, the severity of the pain, and the specific formulation being used.
Fentanyl use in pediatric patients is limited and highly specialized.
Fentanyl should be used with caution in patients with kidney disease. While norfentanyl is inactive, the parent drug's clearance may be reduced. Healthcare providers typically start at the lower end of the dosing range and monitor for signs of opioid toxicity (sedation, respiratory depression).
Since Fentanyl is extensively metabolized by the liver, patients with hepatic impairment (e.g., cirrhosis) may have higher plasma concentrations. Dose reductions of 50% or more may be necessary, and titration should be performed slowly.
Older adults are more sensitive to the effects of opioids and may have reduced renal or hepatic clearance. Healthcare providers usually initiate therapy at very low doses and monitor closely for cognitive impairment, falls, and respiratory issues.
Instructions vary by form, but general guidelines include:
Fentanyl overdose is a medical emergency. Signs include:
Emergency Action: Call 911 immediately. If available, administer Naloxone (Narcan) according to the package instructions. Multiple doses of Naloxone may be required due to Fentanyl's high potency.
> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or the frequency of use without medical guidance. Misuse of Fentanyl can lead to fatal overdose.
Most patients taking Fentanyl will experience some side effects, particularly during the initiation of therapy or after a dose increase. These include:
> Warning: Stop taking Fentanyl and call your doctor or emergency services immediately if you experience any of the following:
Fentanyl carries several of the FDA’s most serious warnings:
Report any unusual symptoms to your healthcare provider. Do not attempt to manage serious side effects at home.
Fentanyl is a high-alert medication. It must only be used by patients for whom it was specifically prescribed. Sharing Fentanyl with others is illegal and can be fatal. Patients should be screened for a personal or family history of substance abuse before starting treatment. It is vital to use the lowest effective dose for the shortest duration possible, although chronic pain patients may require long-term therapy under strict supervision.
The FDA has issued several Black Box Warnings for Fentanyl products. These include the risk of Addiction, Abuse, and Misuse, which can lead to fatal overdose. There is a critical warning regarding Life-Threatening Respiratory Depression, particularly during the first 24-72 hours of treatment or following a dose increase. Accidental Exposure is another major concern; a single dose of Fentanyl, if taken by a child or a non-tolerant adult, can be fatal. Furthermore, Fentanyl should not be used with Benzodiazepines or other CNS depressants unless no other options are available, as this combination significantly increases the risk of death. Finally, Neonatal Opioid Withdrawal Syndrome is a risk for infants born to mothers using Fentanyl long-term during pregnancy.
Patients on Fentanyl require regular clinical monitoring, including:
Fentanyl significantly impairs the mental and physical abilities required for potentially hazardous tasks. Do not drive a car, operate heavy machinery, or participate in dangerous activities until you know how Fentanyl affects you. Dizziness, severe drowsiness, and blurred vision are common.
Do not consume alcohol while using Fentanyl. Alcohol increases the sedative effects of Fentanyl and can lead to a 'dose-dumping' effect with some formulations, or simply synergize with the opioid to stop the patient's breathing. This combination is frequently fatal.
Do not stop taking Fentanyl suddenly if you have been using it for more than a few days. Abrupt discontinuation can lead to severe withdrawal symptoms, including restlessness, lacrimation (tearing), rhinorrhea (runny nose), yawning, perspiration, chills, myalgia (muscle pain), and mydriasis (dilated pupils). Your healthcare provider will provide a gradual tapering schedule to safely reduce the dose.
> Important: Discuss all your medical conditions, including any history of depression, lung disease, or substance use, with your healthcare provider before starting Fentanyl.
For each major interaction, the mechanism usually involves the Cytochrome P450 3A4 pathway. Inhibitors slow the 'exit' of the drug from the body, while inducers speed it up. Management strategies involve either avoiding the combination or performing very careful dose titrations under strict medical supervision.
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking, as Fentanyl has many potentially fatal interactions.
Fentanyl must NEVER be used in the following circumstances:
In these cases, a healthcare provider must perform a careful risk-benefit analysis:
Patients who are allergic to other phenylpiperidine opioids (such as meperidine or sufentanil) may have a higher risk of an allergic reaction to Fentanyl. However, Fentanyl does not typically show cross-reactivity with morphine-based opioids (phenanthrenes), making it an alternative for patients with a true morphine allergy, provided it is administered under medical supervision.
> Important: Your healthcare provider will evaluate your complete medical history, including your lung function and previous experiences with pain medication, before prescribing Fentanyl.
Fentanyl is classified as FDA Pregnancy Category C (under the old system). There are no adequate and well-controlled studies in pregnant women. Prolonged use of Fentanyl during pregnancy can result in Neonatal Opioid Withdrawal Syndrome (NOWS), which can be life-threatening if not recognized and treated. Symptoms in the newborn include irritability, hyperactivity, abnormal sleep patterns, high-pitched cry, tremor, vomiting, diarrhea, and failure to gain weight. Fentanyl should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. It is generally avoided during labor and delivery as it can cause respiratory depression in the newborn.
Fentanyl is excreted in human milk. It can cause sedation and life-threatening respiratory depression in the nursing infant. If a mother must use Fentanyl, the infant should be closely monitored for signs of increased sleepiness, difficulty breastfeeding, or breathing problems. Many experts recommend that women on chronic Fentanyl therapy avoid breastfeeding or use extreme caution under the guidance of a pediatrician.
Fentanyl patches are approved for children aged 2 and older who are opioid-tolerant. However, the safety and efficacy of many transmucosal forms (like Fentora or Lazanda) have not been established in patients under 18. Pediatric patients are at a higher risk of accidental exposure and overdose. Dosing must be calculated with extreme precision by a specialist in pediatric pain management.
Elderly patients (65 and older) may be more sensitive to Fentanyl’s effects, especially respiratory depression and CNS side effects like confusion or falls. Because renal and hepatic function often decline with age, the clearance of Fentanyl may be reduced. Healthcare providers typically start elderly patients at the lowest possible dose and titrate very slowly.
In patients with kidney disease, the clearance of Fentanyl may be reduced. While the metabolites are largely inactive, the accumulation of the parent drug can lead to toxicity. Patients with a GFR (Glomerular Filtration Rate) below 30 mL/min should be monitored very closely, and dose reductions are often necessary.
Fentanyl is primarily metabolized by the liver. In patients with severe hepatic impairment (Child-Pugh Class C), Fentanyl concentrations can be significantly elevated. A dose reduction of at least 50% is often recommended for the initiation of therapy in these patients, with subsequent doses titrated based on clinical response and signs of sedation.
> Important: Special populations require individualized medical assessment. Always inform your doctor if you are pregnant, planning to become pregnant, or have underlying organ dysfunction.
Fentanyl is a pure opioid agonist whose principal therapeutic action is analgesia. It interacts predominantly with the mu-opioid receptors (MOR), which are G-protein coupled receptors. Binding to these receptors inhibits the activity of adenylate cyclase, leading to a decrease in intracellular cAMP. This further results in the closure of N-type voltage-gated calcium channels (reducing neurotransmitter release) and the opening of G-protein-coupled inwardly rectifying potassium (GIRK) channels (causing neuronal hyperpolarization). The net effect is a significant reduction in the transmission of pain signals along the ascending pain pathways and an alteration in the perception of pain in the higher cortical centers.
Fentanyl has a rapid onset of action (especially when given IV or transmucosally) and a relatively short duration of action for single doses due to redistribution. However, with continuous delivery (patches), the effect is sustained. It produces dose-dependent respiratory depression by acting directly on the brainstem respiratory centers. Fentanyl also causes miosis (pinpoint pupils) and may cause a decrease in blood pressure and heart rate.
| Parameter | Value |
|---|---|
| Bioavailability | Transdermal: ~92%; Buccal: ~65%; IV: 100% |
| Protein Binding | 80% to 85% (primarily alpha-1-acid glycoprotein) |
| Half-life | 3–7 hours (IV); 20–27 hours (Transdermal after removal) |
| Tmax | 15–45 min (Transmucosal); 12–24 hours (Transdermal) |
| Metabolism | Hepatic (primarily CYP3A4 to norfentanyl) |
| Excretion | Renal: 75%; Fecal: 9% |
The molecular formula of Fentanyl is C22H28N2O, and its molecular weight is 336.47 g/mol. Fentanyl citrate (the salt form) is a white crystalline powder that is sparingly soluble in water but highly soluble in organic solvents, which contributes to its high lipophilicity and ability to cross the blood-brain barrier rapidly.
Fentanyl is an opioid agonist in the phenylpiperidine class. It is related to other synthetic opioids like sufentanil, alfentanil, and remifentanil, but is distinct from the phenanthrene class (morphine, oxycodone, hydrocodone). Within the therapeutic area of pain management, it is considered a 'strong opioid' used for the highest levels of pain intensity.
Medications containing this ingredient
Common questions about Fentanyl
Fentanyl is a powerful synthetic opioid used primarily for the management of severe, chronic pain and breakthrough cancer pain. It is reserved for patients who are already 'opioid-tolerant,' meaning they have been taking other strong opioids for a significant period. Healthcare providers may use it in hospital settings as an anesthetic or for pain relief during and after surgery. It is not intended for mild or temporary pain, such as headaches or minor injuries. Because of its extreme potency, it is only used when other pain management options are insufficient.
The most common side effects of Fentanyl include nausea, vomiting, constipation, and extreme sleepiness or somnolence. Many patients also experience dizziness, sweating, and a dry mouth. While nausea often improves as the body adjusts to the medication, constipation is a persistent issue that usually requires treatment with laxatives. Some patients may also feel confused or have trouble with balance. Because Fentanyl affects the central nervous system, it can significantly impair your ability to drive or think clearly.
No, you should never drink alcohol while using Fentanyl. Alcohol and Fentanyl both depress the central nervous system and the respiratory system. When taken together, they can cause your breathing to slow down to dangerous levels or stop entirely, leading to coma or death. Additionally, alcohol can cause certain Fentanyl formulations to release the medication too quickly into your bloodstream. This combination is one of the most common causes of fatal opioid overdoses.
Fentanyl is generally not recommended during pregnancy unless the benefits clearly outweigh the risks, and it should only be used under strict medical supervision. Long-term use of Fentanyl during pregnancy can cause the baby to be born with Neonatal Opioid Withdrawal Syndrome (NOWS), a life-threatening condition where the infant goes through withdrawal. It can also cause respiratory depression in the baby if used near the time of delivery. Mothers who are using Fentanyl should discuss pain management alternatives and the risks to their fetus with their obstetrician. Breastfeeding is also discouraged as Fentanyl passes into breast milk.
The onset time for Fentanyl depends entirely on how it is administered. When given intravenously in a hospital, it works almost instantly. Transmucosal forms, like buccal tablets or lozenges, typically begin to provide relief within 15 to 30 minutes, which is why they are used for breakthrough pain. However, the transdermal patch is a slow-release system; it can take 12 to 24 hours to feel the full effects after applying the first patch. Because of this delay, patches are never used for sudden or acute pain.
You should never stop taking Fentanyl abruptly, especially if you have been using it for a long time. Sudden discontinuation can trigger severe withdrawal symptoms, including anxiety, tremors, muscle aches, sweating, runny nose, and diarrhea. While these symptoms are rarely life-threatening for adults, they are extremely uncomfortable and can lead to a relapse in drug use. Your doctor will provide a tapering schedule to slowly lower your dose over several weeks to allow your body to adjust safely.
If you miss a dose of Fentanyl, what you should do depends on the form you are using. For a transdermal patch, apply a new one as soon as you remember and note the new time for your next change. Never apply two patches at once to 'catch up.' For breakthrough medications like tablets or sprays, these are taken as needed, so you simply wait for the next time you feel pain. Always contact your healthcare provider if you are unsure how to handle a missed dose to avoid withdrawal or accidental overdose.
Weight gain is not a common direct side effect of Fentanyl. However, some patients may experience fluid retention (edema), which can lead to a slight increase in weight. Additionally, because Fentanyl causes sedation and can decrease physical activity, some patients might gain weight over the long term. Conversely, some patients experience chronic nausea or a loss of appetite, which can lead to weight loss. If you notice significant changes in your weight while taking Fentanyl, you should discuss them with your doctor.
Fentanyl has many serious drug interactions and should be used with caution alongside other medications. It is particularly dangerous to mix Fentanyl with benzodiazepines, sleep aids, or other opioids. Medications that affect liver enzymes (specifically CYP3A4), such as certain antibiotics, antifungals, and HIV medications, can cause Fentanyl levels to rise to toxic levels. You must provide your doctor with a full list of all prescriptions, over-the-counter drugs, and herbal supplements you are taking to ensure your safety.
Yes, Fentanyl is available in several generic forms, including the transdermal patch and the injectable solution. Many of the transmucosal forms, such as the lozenges and buccal tablets, also have generic versions available (e.g., generic Actiq or Fentora). Generic medications are required by the FDA to have the same active ingredient, strength, and effectiveness as the brand-name versions. Using generic Fentanyl can significantly reduce the cost of treatment for patients with chronic pain.