How long does fentanyl stay in your system?

The amount of time it takes for fentanyl to leave your system depends on several factors. Read more here.

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Fact checked by
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Fentanyl is a drug that is commonly added to other drugs, like cocaine and heroin. It can be extremely dangerous for people who use those substances, leading to overdose and death. Learning more about fentanyl and its effects can help reduce the risk of opioid overdose.  

What is fentanyl?

Fentanyl is a synthetic opioid that was originally developed as a painkiller for surgical patients. It’s between 50 and 100 times more potent than morphine. Doctors prescribe pharmaceutical fentanyl for pain management treatment, usually to cancer patients. 

The illegally made fentanyl is the one that’s such a cause for concern. This illicit type has entered the drug supply and led to rising overdose death rates. When people who use drugs unknowingly consume something laced with fentanyl, they are at a greatly increased risk of overdose.    

How Much Fentanyl Can Kill You?

As with any other drug, the amount of fentanyl that will lead to death depends on many personal factors. Someone who is already tolerant of opioids would be able to take a larger dose of fentanyl without suffering severe adverse effects, for example. 

That said, fentanyl is an extremely powerful drug. It only takes a small amount to cause serious harm to anyone, regardless of opioid tolerance. 

The Drug Enforcement Agency (DEA) considers 2 mg of fentanyl or more to be a lethal dose. Given that a typical drug dose is between 100 mg and 250 mg, a dose that’s as little as 0.8% fentanyl can be deadly. It sounds like an insignificant amount, but it could have devastating effects. Consuming that much fentanyl is likely to cause a life-threatening overdose

For someone who isn’t tolerant of opioids, smaller doses of fentanyl could cause death. As little as 0.5 mg of fentanyl leads to an extreme risk of overdose and death for someone without opioid tolerance. In short, the amount of fentanyl considered lethal depends on the person. Even trace amounts can be deadly under the wrong circumstances. 

How long does fentanyl stay in your system?

The amount of time it takes for fentanyl to leave your system also depends on several factors. Some variables to consider include:

  • Height
  • Weight 
  • Age
  • Genetics
  • Dosage
  • Frequency of drug use
  • Metabolism
  • Use of other drugs
  • Overall health 

The method used to administer the drugs is also important. Fentanyl will stay in your system longer if you use a patch or lozenge compared to intravenous use. When you use intravenous drugs containing fentanyl, the compound will stay in your system for up to 24 hours. With a patch or lozenge, it can take up to 36 hours for fentanyl to leave your system entirely. 

You won’t feel the effects of the drug for all that time, though. The side effects of fentanyl typically only last between four and six hours.

Will fentanyl show up on a blood test?

As your body breaks down the fentanyl, the drug leaves behind trace amounts known as metabolites. These metabolites are just a byproduct of the fentanyl breaking down and won’t affect how you feel. They can, however, impact the results of a drug test. 

Most standard drug tests don’t look for fentanyl. Only an advanced drug test is likely to detect its use. If you are subjected to an advanced drug test, you can expect a blood test to detect fentanyl for up to 12 hours after use. Other tests, like urine and saliva drug tests, can identify fentanyl after longer periods. Hair tests can find fentanyl use for up to 90 days.

What are fentanyl withdrawal symptoms?

Suddenly stopping or reducing your fentanyl use can lead to withdrawal symptoms, which are similar to those of other opioids. They include strong cravings for the drug, nausea, vomiting, sweating, insomnia, muscle ache, fever, and a dysphoric mood. These symptoms can be painful and even dangerous. 

Fentanyl withdrawal symptoms typically show up as quickly as six to 12 hours after your last dose. Depending on the route of administration, some heavy users may experience withdrawal symptoms in as little as 30 to 60 minutes. They’re most severe over the first three days and gradually get less intense over about a week. After that period of acute fentanyl withdrawal symptoms, some people experience post-acute symptoms for weeks or even months. The post-acute fentanyl withdrawal symptoms include trouble sleeping, dysphoria, anxiety, and an inability to feel pleasure, also known as anhedonia. 

Dealing with these withdrawal symptoms is part of what makes addiction treatment so difficult. Having treatment options other than rehab can make a big difference.  

Dealing with fentanyl addiction

Ophelia is here to help manage addiction treatment at home with a private, personalized approach to recovery. If you struggle with fentanyl addiction, reach out to Ophelia for support and information about treatment options, or refer to the Substance Abuse and Mental Health Services Administration (SAMHSA) site for more resources, including access to a 24/7 helpline.


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