Updated on February 6, 2024
5 min read

How Long Does Fentanyl Stay in Your System?

How Long Does Fentanyl Stay in Your System (Drug Test Detection Time)?

The amount of time fentanyl stays in your system varies based on several individualized factors. Factors include body fat, age, gender, diet, genetics, and more. 

Urine Test 

This drug test detects fentanyl in urine within 24 hours of the last use. Fentanyl remains detectable in the body for up to 72 hours. 

Saliva Test 

Fentanyl drug use can’t be consistently detected by drug testing. Fentanyl, even when taken orally, goes through extensive bodily filtering.

This process leaves behind undetectable traces of Fentanyl and its metabolites. 

Blood Test 

Blood drug tests detect fentanyl for up to 72 hours. 

Hair Test

Hair drug tests are often used in tandem with positive urine or blood tests. This test helps to establish a brief history of fentanyl use and reveal substance abuse patterns.

Fentanyl isn’t detectable in hair for the first few days after the last use. However, once fentanyl is in the hair, it can be detected for up to 3 months.

Drug screenings are designed to detect fentanyl and its metabolites:

  • Norfentanyl
  • Desropionylfentanyl

Repeated fentanyl drug abuse increases the level of these metabolites. This increase makes positive fentanyl drug tests more likely.

What is The Half-Life of Fentanyl? 

The half-life of fentanyl varies with each route of administration. 

  • IV fentanyl: A half-life of approximately 8 hours.
  • Oral tablet: A half-life of approximately 20 hours.

The time differences for the half-lives are due to the bioavailability of the drug. Bioavailability is defined by how much of a compound can be effectively absorbed by the body.

IV fentanyl has a much higher level of bioavailability than other routes. Meaning the body absorbs the substance quicker.

Conversely, oral administration of fentanyl has much lower bioavailability. Therefore, it takes longer for the body to absorb fentanyl.

Because of bioavailability, saliva drug tests are ineffective at detecting fentanyl. Only a small amount of fentanyl remains in saliva after administration.


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How Long Do the Effects of Fentanyl Last? 

The length of time it takes to feel the effects of fentanyl depends on the type you take. It could be instant, or it could take a few days. 

Here are the four ways you can take fentanyl:

  • IV fentanyl
  • Oral tablet
  • Nasal spray
  • Transdermal patch

When injected directly into your veins, the IV fentanyl gives you the quickest pain relief. The effects can be felt immediately and last up to 4 hours.

The oral tablet takes about 15 to 30 minutes. However, the effects wear off after 4 to 6 hours.

When ingested nasally, you can feel the effects of fentanyl around the 60-minute mark. Nasal fentanyl lasts almost as long as the oral tablet.

Fentanyl patches can take up to two days before it starts working. However, the effects can last for 17 hours or longer.

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What is Fentanyl, and How Does it Work?

Fentanyl is a pain-relieving narcotic that is 50 to 100 times stronger than morphine. It is also known as:

  • Lonsys
  • Subsys
  • Duragesic

Fentanyl attaches to specific opioid receptors and activates them. These receptors are responsible for pain and emotion.

Fentanyl then boosts dopamine release from a particular nerve cell in our brain’s reward center. This increased dopamine activity links with a reinforcing sense of euphoria.

However, fentanyl can also reduce breathing. Considering fentanyl’s potency, this significantly increases the risk of overdose.8

Side Effects

Fentanyl is a schedule 2 prescription drug with several serious side effects. 

Here are the most common side effects:

  • Respiratory depression
  • Drowsiness 
  • Nausea 
  • Sluggishness 
  • Confusion 
  • Distorted senses
  • Constipation 
  • Substance use dependency 
  • Overdose

Overdose Risk

Fentanyl’s potency makes overdose a risk. Especially if the individual using mistakes it for another drug.8

Combining substances like alcohol and benzodiazepines with fentanyl also boosts the risk of overdose. As well as death by respiratory arrest.

The following are signs and symptoms of Fentanyl overdose:9

  • Severely slowed or stopped breathing
  • Blue lips and skin color
  • Cold, clammy skin
  • Constricted pupils
  • Stupor
  • Seizures
  • Loss of consciousness
  • Coma

Effects of Long-Term Fentanyl Use

The amount of time a fentanyl high lasts varies based on individual health factors and by route of administration.

  • IV fentanyl: The effects of IV fentanyl can be felt immediately and persist for up to 4 hours. IV Fentanyl is the most common method of administration in a healthcare setting.
  • Oral fentanyl: The effects of orally delivered fentanyl can take up to 30 minutes to become apparent. The intensity of the high and duration of it will also vary if the individual allows the drug to be absorbed through the gums or if they swallow the drug whole. On average, fentanyl highs last longer if swallowed due to bioavailability, but it has intenser effects when taken intravenously. 
  • Nasal fentanyl: When ingested nasally, fentanyl peaks around the 60-minute mark. 

Long-term fentanyl use has its side effects and dangers. These long-term dangers are prevalent among individuals with drug abuse issues. 

However, the long-term effects are also found in individuals prescribed Fentanyl for chronic pain. Long-term fentanyl effects include:

  • Gastrointestinal Inflammation 
  • Sleep apnea 
  • Weakened immune system 

These are just a few of the potential hazards of long-term fentanyl use. In many cases, addiction therapies are needed to assist in recovery.

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Updated on February 6, 2024
9 sources cited
Updated on February 6, 2024
  1. Baldini, Angee, et al. “A Review of Potential Adverse Effects of Long-Term Opioid Therapy: A Practitioner's Guide.” The Primary Care Companion for CNS Disorders, Physicians Postgraduate Press, 2012.
  2. Lee, Jaewon, et al. “Clinical Usefulness of Long-Term Application of Fentanyl Matrix in Chronic Non-Cancer Pain: Improvement of Pain and Physical and Emotional Functions.” Clinics in Orthopedic Surgery, The Korean Orthopaedic Association, 2016.
  3. Peng, Philip W. H., and Alan N. Sandler. “A Review of the Use of Fentanyl Analgesia in the Management of Acute Pain in Adults .” Anesthesiology, American Society of Anesthesiologists, 1999.
  4. Schifano, Fabrizio, et al. “Assessing the 2004-2018 Fentanyl Misusing Issues Reported to an International Range of Adverse Reporting Systems.” Frontiers in Pharmacology, Frontiers Media S.A., 2019.
  5. Schwartz, J G, et al. “Measurements of Fentanyl and Sufentanil in Blood and Urine after Surgical Application. Implication in Detection of Abuse.” National Library of Medicine, 1994.
  6. Silverstein, Jeffrey, et al. “An Analysis of the Duration of Fentanyl and Its Metabolites ... : Anesthesia & Analgesia.” LWW, 1993.
  7. Drug Testing, MedlinePlus, 2020.
  8. Fentanyl, MedlinePlus, 2021.
  9. Drug Enforcement Administration, Drugs of Abuse, 2017.

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