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How Long Does Fentanyl Stay in Your System?

Peter Manza, PhD profile image
Reviewed By Peter Manza, PhD • Updated Feb 24, 2024 • 14 cited sources

Fentanyl generally takes about 12 to 35 hours to completely metabolize out of the system, depending on the dose and other factors.[3]

Fentanyl remains detectable in urine drug tests for two to three days after use, but it can show up in hair sampling tests for up to 90 days.[6,13]

What Is Fentanyl’s Half-Life?

Fentanyl is a synthetic opioid that is becoming an increasingly common drug of misuse on its own and in combination with other substances, like heroin. It is relatively short-acting compared to other drugs of misuse, meaning that its impact is at its strongest relatively quickly after ingestion, and the half-life is short.[1]

Fentanyl has a half-life lasting between three and seven hours.[3] Half-life is a measurement of how long your body needs to process half of a drug dose.

Between 94% and 97% of a drug will be eliminated from the system after four to five half-lives, bringing the concentration low enough in the body to be clinically irrelevant.[2]

How Long Does Fentanyl Stay in Your System? 

Because it takes four to five half-lives for the drug to be fully processed out of the system, and fentanyl has a half-life of three to seven hours, it could take fentanyl anywhere from 12 to 35 hours to fully be eliminated from the body.[2,3]

Researchers say a drug’s half-life can be influenced by several factors, including the following:[14]

  • Drug distribution (or how much you took)
  • Age
  • Use of concurrent medication
  • Presence of liver or kidney disease

These factors could make fentanyl stay in your body longer than typical, or they could allow you to clear the drug quicker than expected.

How Long Will Fentanyl Be Detectable on Different Types of Drug Tests? 

Different types of drug tests assess different types of samples for the presence of drugs, but not every fluid or substance tested will show the presence of fentanyl for hours or even days after ingestion, no matter what the method. 

Here are some of the different types of blood tests and the lengths of time that fentanyl will show up on these tests: 

Test TypeDetection Window
BloodUp to 24 hours
HairUp to 90 days
SalivaUp to 72 hours
UrineUp to 3 days
  • Blood: Fentanyl can be detected in blood for up to 24 hours after last use.
  • Hair: Fentanyl can be detected in hair for up to 90 days after use. This is because drug metabolites can be stored in hair follicles for an extended period of time.[13]
  • Saliva: Fentanyl can be detected in saliva for up to 72 hours after use, but it also may not be detected at all even immediately after use.[6]
  • Urine: Fentanyl can be detected in urine for up to two to three days after use, depending on the dose and frequency of use.[6]

Why Would Someone Drug Test for Fentanyl? 

There are several reasons why someone might request a drug test to check for fentanyl. These include the following: 

  • Medical purposes: If someone is prescribed fentanyl as a pain medication, their doctor may order drug testing to monitor their use and ensure they are taking the medication as prescribed. This is to make sure they are not currently misusing opioids before giving them a prescription for another opioid. 
  • Treatment for opioid use disorder: Entering treatment starts with gathering baseline information. It is helpful to know how much and what kinds of drugs are in the system at the beginning of treatment and then watch those levels drop as course of care continues. Follow-up tests may be given to ensure ongoing abstinence from substance misuse. 
  • Workplace safety: In some industries, such as transportation or heavy machinery operation, drug testing is required to ensure employees are not under the influence of drugs that could impair their ability to perform their jobs safely.[7]
  • Law enforcement purposes: When entering a prison facility or on parole, law enforcement may use drug testing to identify people who are actively using substances in violation of the rules. 
  • Forensic investigations: Fentanyl may be detected in post-mortem drug testing as part of an investigation into the cause of death.

Not all drug tests are created equal, so it may be necessary to repeat a drug test in any setting to ensure that there are no false positives or false negatives. 

What Factors Could Impact the Timeline for How Long Fentanyl Stays in the System?

Several factors can impact how long fentanyl stays in the system. These factors include the following:

  • Dosage: The higher the dosage of fentanyl, the longer it may take to be eliminated from the body.
  • Frequency of use: Frequent use of fentanyl can lead to accumulation in the body, which may prolong its elimination time. In fact, long-time users of fentanyl often take days, if not weeks, longer than those who use the drug infrequently to fully eliminate fentanyl from their systems.[8]
  • Method of administration: Intravenous fentanyl use may be metabolized more quickly than fentanyl taken orally. This means that fentanyl that is injected may leave the system more quickly compared to fentanyl taken in pill form. 
  • Age: Older adults may have a slower metabolism, which could prolong the elimination time of fentanyl.
  • Weight: A person’s weight and body mass index (BMI) can impact how quickly drugs are metabolized and eliminated from the body. In general, people with higher body fat percentages may eliminate drugs more slowly.
  • Liver function: The liver plays a key role in metabolizing drugs, including fentanyl. People with liver disease or reduced liver function may eliminate fentanyl more slowly.
  • Other medications: Some medications can interfere with the metabolism of fentanyl, which could impact how long it stays in the system.

How Does Fentanyl Affect the Body? 

Fentanyl is a synthetic opioid that works by binding to specific receptors in the brain and central nervous system called mu-opioid receptors.[9] These receptors are responsible for regulating pain perception, reward, and other physiological responses.

When fentanyl binds to the mu-opioid receptors, it activates them and produces a range of effects, including pain relief, sedation, and euphoria. Fentanyl’s effects are more potent and rapid than the effects of some other opioids like morphine and oxycodone due to its high affinity for the mu-opioid receptors.

In addition to its effects on pain perception, fentanyl also has other physiological effects. It can reduce breathing, heart rate, and blood pressure. This can be dangerous at high doses or if fentanyl is taken in combination with other drugs that have similar effects.

Fentanyl is metabolized in the liver, primarily by the enzyme CYP3A4.[10]  It is eliminated from the body through urine and feces. Depending on the frequency of use, levels of fentanyl can build up in the system, so the person taking the substance may not notice its effects but could still potentially overdose. 

Other physical issues often experienced by people taking fentanyl include the following: 

  • Pinpoint pupils
  • Respiratory depression
  • Nausea and vomiting
  • Constipation
  • Low blood pressure
  • Muscle rigidity

Different people will experience different effects when taking fentanyl. Those effects may be more or less intense and last for different lengths of time based on various factors. 

How Is Fentanyl Absorbed Through the Body? 

Fentanyl can be absorbed through various routes of administration, and the absorption process will vary depending on the method. The most common routes of administration for fentanyl include the following:

  • Intravenous (IV) injection: When fentanyl is ingested using a needle, the effect is rapid in onset. The drug is usually more quickly metabolized out of the body compared to other methods. 
  • Transdermal patch: Fentanyl can be delivered through a transdermal patch. This is placed on the skin and releases the drug over a period of several days. The patch allows for slow and steady absorption of fentanyl into the bloodstream.

    The ongoing nature of administration means that levels remain consistent in the body for as long as the patch is viable. This is usually reserved for cancer patients and chronically ill patients with intense pain that is not managed through other methods.
  • Pill form: Fentanyl can be administered as sublingual or buccal tablets, which are placed under the tongue or against the cheek, respectively. This method allows for rapid absorption through the mucous membranes in the mouth.

    In some cases, fentanyl is used to create fake pills on the black market designed to look like Vicodin or OxyContin.[11] These pills are swallowed, digested, and released into the system. 
  • Intranasal spray: Fentanyl can be administered as an intranasal spray, which is absorbed through the mucous membranes in the nose. This method allows for rapid onset of effects. It is commonly used in emergency situations.

Regardless of the route of administration, once fentanyl enters the bloodstream, it is distributed throughout the body and can cross the blood-brain barrier to reach the central nervous system. The speed and extent of distribution will vary based on individual factors, such as the dose, route of administration, and personal characteristics of the user, including weight, age, and liver function.

Finally, the liver processes fentanyl and secretes it as waste until it is fully out of the body. 

MAT for Fentanyl Detox

Suboxone, a medication that combines buprenorphine with naloxone, is a medication used in Medication for Addiction Treatment for opioid use disorder. MAT combines the use of medications like Suboxone with behavioral therapy and counseling to provide a comprehensive approach to recovery.

Buprenorphine works by binding to the same opioid receptors in the brain as fentanyl.[12] However, because it is a partial agonist, it produces less euphoria and fewer physical effects than full agonist opioids. This means that it can help to reduce cravings and withdrawal symptoms without producing the same level of dependence and OUD that comes with regular use of drugs like heroin and fentanyl.

Naloxone, which is included in Suboxone, is an opioid antagonist that can help to prevent misuse of the medication. If someone tries to inject or misuse Suboxone, the naloxone will be activated and block the effects of the buprenorphine. This will cause immediate withdrawal symptoms.

MAT with Suboxone and other medications can be an effective approach to opioid use disorder treatment because it can do the following:

  • Reduce cravings and withdrawal symptoms
  • Prevent relapse
  • Improve retention in treatment
  • Provide a stable and controlled environment
  • Decrease the risk of overdose

It’s important to note that MAT is not a one-size-fits-all approach. Different individuals may respond better to different medications, doses of medication, or approaches to treatment. It can take time to dial in the right dose and then begin the weaning process, if appropriate. Many people remain on Suboxone indefinitely, however, as it continues to support their recovery.

Fentanyl Rehabilitation Can Start Today

Bicycle Health specializes in helping people living with an opioid use disorder to get the help they need to safely stop using the drug. Contact Bicycle Health today to learn more about MAT and how it can help you or your loved one.

Reviewed By Peter Manza, PhD

Peter Manza, PhD received his BA in Psychology and Biology from the University of Rochester and his PhD in Integrative Neuroscience at Stony Brook University. He is currently working as a research scientist in Washington, DC. His research focuses on the role ... Read More

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  2. Half Life. StatPearls. June 2022. Accessed March 2023.
  3. Fentanyl. National Library of Medicine. StatPearls. Accessed March 2023.
  4. Opioid Half-Lives and Hemlines: The Long and Short of Fashion. Anesthesiology. May 2015. Accessed March 2023.
  5. Comparison Between Intravenous Morphine Versus Fentanyl in Acute Pain Relief in Drug Abusers With Acute Limb Traumatic Injury. World Journal of Medicine. 2019. Accessed March 2023.
  6. An analysis of the duration of fentanyl and its metabolites in urine and saliva. Anesthesiology and Analgesia. Mar 1993. Accessed Mar 2023.
  7. Drug Testing Resources. Substance Abuse and Mental Health Services Administration. February 2023. Accessed March 2023.
  8. Protracted Renal Clearance of Fentanyl in Persons with Opioid Use Disorder. Drug and Alcohol Dependence. July 2020. Accessed March 2023.
  9. Kinetics and Mechanism of Fentanyl Dissociation from the μ-Opioid Receptor. American Chemical Society. November 2021. Accessed March 2023.
  10. Opioid Pharmacokinetic Drug-Drug Interactions. American Journal of Managed Care. September 2011. Accessed March 2023.
  11. USA TODAY Op-Ed: As Illegal Drug Trade Goes From the Corner to the Web, Rising Deadly Threat of Fake Pills. United States Department of Justice. October 2021. Accessed March 2023.
  12. Buprenorphine for Opioid Addiction. Pain Management. July 2012. Accessed March 2023.
  13. Opioid Testing. September 2022. Accessed January 2024.
  14. The Practical Importance of Half-Life in Psychopharmacology. The Journal of Clinical Psychiatry. July 2022. Accessed January 2024.

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