How Long Does Fentanyl Stay in Your System? Side Effects and Dangers

what does fentanyl look like
Fentanyl Overdose Symptomes

Chronic conditions that bring severe pain to people often need stronger remedies, so despite the extreme risk of addiction associated with opioids, it’s one of the few medications that can offer lasting relief to patients. Out of all the opioids — natural or synthetic — Fentanyl is one of the most popular painkillers in hospital settings. 

What is Fentanyl? 

Fentanyl is a synthetic opioid analgesic that is the go-to choice for managing illnesses or postsurgical pain, especially since its effects are 50 to 100 times stronger than morphine. Known as a Schedule II controlled substance in the USA, it’s a widely used medication that can effectively dull pain. However, its drawback is its high potential for developing drug dependency. 

How Long Does Fentanyl Stay in Your System? 

Seeing as Fentanyl is a potent, synthetic opioid, amounts ranging from 12 to 100 micrograms can last an hour. It changes every 72 hours as the liver breaks down the drug, so studies suggest that Fentanyl can last in your system for up to four days. Here are different drug tests that can detect Fentanyl: 

  • Blood – When taking a blood test, Fentanyl can show up in the results up to 48 hours after the last consumption.

  • Urine – Urine can hold traces of Fentanyl longer, so results can show up positive for up to three days from the last intake. That’s why employers often choose urine tests to check for drug abuse in their company.

  • Hair – It’s the most uncommon drug test, though it proves to be the most effective at testing for abuse since it can detect substances like Fentanyl for up to a whopping three months since the last use. 

What are the Factors that Influence Detection Time? 

Different drugs and their doses impact the way the body breaks it down, so detecting the presence of Fentanyl largely depends on the following: 

  • Dose – The higher the dose you consume, the longer it will stay in your system.

  • Metabolism – Some people can break down substances faster than others due to healthy kidney function, so those with compromised livers may have a slower metabolism. This results in substances like Fentanyl staying longer in your system.

  • Location of the Patch – For transdermal patches, where you stick it on will change the absorption rate. This means the thicker the skin and the more fat you have, the slower it will absorb Fentanyl into your body. 


Fentanyl: The Good, the Bad, and the Deadly 

You can also recognize the oral version of Fentanyl in pharmacies as Abstral, Actiq, Fentora, or Onsolis, appearing either as tablets, films, or lozenges. 

You can also get transdermal patches for patients who prefer smoother drug delivery with fewer interactions, which brand names like Duragesic or Ionsys offer. Whether you take it orally or transdermally, it’s important to practice extreme caution since doses as little as 2 mg can lead to fatal results. 

Even when taken in proper amounts with strict medical monitoring, Fentanyl can still deliver potent results and cause the following side effects: 

  • Redness and irritation of your skin where you apply the patch
  • Nausea
  • Vomiting
  • Tiredness
  • Dizziness
  • Trouble sleeping
  • Constipation
  • Increased sweating
  • Feeling cold
  • Headache
  • Diarrhea
  • Loss of appetite

These side effects are typically common and will fade within a few days to weeks, though if the symptoms worsen, it’s crucial to seek medical attention immediately. 

fentanyl half life
How Long Does Fentanyl Stay in Your System

What are the Serious Side Effects that Warrants Your Concern? 

Fentanyl can quickly turn from a life-saving medication into a dangerous drug, so it’s important to keep a keen eye on someone who is prescribed Fentanyl monitor the following graver side effects: 

  • Serious breathing problems
  • Dizziness, fainting, or confusion
  • Severely low blood pressure
  • Muscle weakness
  • Abdominal pain

What are the Symptoms of Dependence? 

Fentanyl works by activating certain opioid receptors in the brain, which primarily manages your pain receptors and emotions. When it interacts with these receptors, it can invite an encompassing wave of euphoria since it releases more dopamine, which is why people often grow dependent on Fentanyl in the first place. 

The list below explores some common symptoms that indicate a person is growing addicted to Fentanyl. 

  • Restlessness
  • Irritability
  • High blood pressure
  • Fast breathing rate
  • Fast heart rate
  • Dilated pupils
  • Nausea, vomiting, loss of appetite
  • Diarrhea
  • Stomach cramps
  • Sweating
  • Chills
  • Muscle aches

Similarly, the euphoric effects and Fentanyl’s potency also increases your risk of overdose. With that in mind, the signs below should let you know when a person is suffering from an overdose: 

  • Drowsy consciousness with speech inabilities
  • Lethargy and physical limpness
  • Skin discoloration, wherein darker-skinned people look ashen, while lighter-skinned people look bluish purple
  • Pale and clammy skin
  • Fingernails and lips turn blue or purplish black
  • Loss of consciousness
  • Pulse (heartbeat) is slow, erratic, or not there at all
  • Making a snore-like gurgling noise or “death rattle,” choking sounds
  • Non-responsive to an outside stimulus
  • Very slow, shallow, erratic, or stopped breathing
  • Vomiting



Fentanyl is a widely-used medical drug that effectively relieves extremely painful symptoms, allowing people with conditions like cancer to find relief. While it serves as a silver lining to those struggling with painful illnesses, it’s important to acknowledge the severe addictive qualities and high risk of overdose when it’s abused.