Heroin addiction is a continuing problem in society. America has, for many years, been in the grip of an opioid crisis, fuelled by the rise of fentanyl. Problems around opiates exist in the UK, with 2,551 deaths involving them, according to the latest figures.

People can take fentanyl knowingly, or it is in drugs such as heroin and cocaine without the user knowing, increasing the dangers of taking the drug. Cocaine may seem like a less risky drug than heroin, but deaths related to it rose by 30.5% from 2022 to 2023.

If you are worried about the dangers of this opioid, you should know how to get fentanyl out of your system, how long it stays in there and what available support there is.

What is Fentanyl?

Fentanyl is a synthetic opioid, meaning that it is man-made in a lab. It is extremely potent, around 100 times stronger than morphine and 50 times stronger than heroin.

It is used in medicine as a powerful painkiller, prescribed to treat extreme pain, such as after a serious injury. It can also be prescribed to treat long-term pain if weaker painkillers aren’t working. Over the last fifteen years, however, it has become more common on the street – leading to multiple crises in the USA as overdoses have soared.

That is the true danger of fentanyl: overdosing. Due to its potency, the risk of overdose is high, especially when it is mixed with other substances and users are unaware.

How Does Fentanyl Work in the Body?

Fentanyl can be absorbed into the body through inhalation, ingestion and through the skin. Prescription fentanyl comes in the form of lozenges, pills and a nasal spray. These are used when the pain the user is going through is short-term. Fentanyl also comes in skin patches to treat long-term pain as the patches are slow-release.

On the street, fentanyl usually comes in powder or pill form.

If taken orally, absorption takes 1 to 6 hours, whilst injection takes a few seconds. Your body absorbs fentanyl via inhalation in a few minutes.

Fentanyl is metabolised in the liver, broken down into metabolites which remain long after but are inactive. Fentanyl is then eliminated from the body via urine, faeces and sweat.

This opioid is incredibly potent, making it dangerous. As little as two milligrams can be a lethal dose, and many illicit fentanyl pills contain much more than this.

How Long Does Fentanyl Stay in Your System

So, how long does fentanyl stay in your system?

This information relies on knowing the elimination half-life of fentanyl, which means how long it takes half of a single dose to leave your body. When injected, fentanyl has an elimination half-life of 2-4 hours, meaning it takes around 11-22 hours to leave your system. If using a patch or lozenge, the elimination half-life is 7-17 hours, so it will take up to 36 hours to leave your system.

Now, the detection time of fentanyl is a different thing altogether. When your body breaks down fentanyl, it leaves metabolites that can be detected through different biological samples long after you stop taking the drug.

The fentanyl detection time in a urine test is up to 72 hours; other timeframes for different samples include:

  • Blood: 5-48 hours.
  • Saliva: 1-4 days.
  • Hair: up to 90 days (3 months).

These detection and half-life figures can change due to several factors. If you have a drug addiction and take fentanyl more, it will stay in your system longer. Your metabolism, size of dosage, how you take it, and use of other drugs can all affect how long fentanyl stays in your system.

Factors That Influence How Long Fentanyl Stays in the Body

Many factors can affect how long fentanyl stays in your body. These include:

  • Dosage and frequency – Chronic use of fentanyl can lead to a build-up in your body, meaning it stays around for longer. Higher doses will also increase the detection time.
  • Method of use – Depending on how you take it, fentanyl can last for different amounts of time. Injection is faster acting and goes quicker whilst slow-release patches can leave fentanyl in you for longer.
  • Metabolism and body composition – Body fat and liver function can affect the elimination of fentanyl, along with how good your metabolism is.
  • Hydration and kidney function – Fentanyl can’t be flushed out quicker by going to the toilet more. However, good hydration helps the kidneys function more efficiently, improving the metabolising and removal of fentanyl.

How is Fentanyl Detected in Drug Tests?

Blood, saliva and hair are all samples used in drug tests. The most common type of drug test is a urine test.

So, does fentanyl show up in a drug test?

Most standard drug tests don’t detect fentanyl as they are designed to detect morphine metabolites, which fentanyl doesn’t produce. An expanded opioid panel is needed to detect synthetic and semi-synthetic opioids such as fentanyl. These panels will detect the presence of metabolites produced by fentanyl.

Fentanyl analogues, such as carfentanil, may have different detection times as they are similar to fentanyl but have a different chemical structure.

How to Safely Detox from Fentanyl

Fentanyl withdrawal occurs when you suddenly stop taking it because your body has become used to the drug. Once it is gone, there is an imbalance in your body and withdrawal symptoms occur as everything goes into overdrive.

Fentanyl withdrawal is particularly severe because fentanyl is an incredibly addictive substance and very potent. For these reasons, withdrawal can be very dangerous.

Because it is so dangerous, medically assisted drug detox is recommended. It is the safest option for managing symptoms, where you can take medication to alleviate symptoms and be under constant watch by staff.

During the fentanyl withdrawal timeline, you may experience:

  • Sweating
  • Nausea
  • Anxiety
  • Cravings
  • Stomach cramps
  • Sleeping issues

The symptoms you experience can be severe, leading to medical emergencies. Using rehab programmes like Ocean Recovery offers the safest and most effective method of fentanyl detox.

Seeking Help for Fentanyl Addiction

If you are struggling with fentanyl use, then you should seek professional treatment. It can take hold quickly, and it is very hard, as stated above, to go cold turkey without the help of experts.

Ocean Recovery is a drug rehab that provides leading addiction recovery services. With us, you’ll gain access to a wide variety of treatment options, including detox, therapies and long-term support. The addiction treatment programme you undertake will be personalised, meaning we consider everything about your situation and provide you with the best path forward.

With the right guidance and support, recovery is possible.

Get Help With Fentanyl Now

The question of how long fentanyl stays in your system depends on many factors, including how you take the drug and how well your body metabolises it. No matter what, the detection times depend on what biological sample is used to test for it.

Fentanyl is a serious drug, very dangerous and should be avoided if possible. If you are struggling with fentanyl addiction, professional support is available.

Ocean Recovery is a private drug and alcohol rehab that can help. For more information, call now at 0800 880 7596.

John Gillen - Director at Ocean Recovery

John Gillen - Author - Last updated: April 3, 2025

John is one UK’s leading professionals in the addiction recovery industry. Pioneering new treatment techniques such as NAD+ and ongoing research into new therapy techniques such as systematic laser therapy, John is committed to providing the very best treatment for people throughout the UK and Europe. During his extremely busy schedule, John likes to regularly update our blog section with the latest news and trends in the industry to keep visitors to our site as well informed as possible on everything related to addiction treatment.