You may have heard of fentanyl, but many are still unaware of the potential risks that come with fentanyl use and how long it can stay in the body.

In this blog, we’ll talk about what fentanyl is, why it’s so dangerous, how long it can be detected in your system, and what steps to take if you suspect someone is having a fentanyl overdose.

What is Fentanyl?

Fentanyl is a type of synthetic opioid. In the UK, the NHS will prescribe fentanyl to those who are experiencing severe pain. It can come in various forms, which may include lozenges, patches, injections, and nasal sprays.

What Does Fentanyl Do?

Fentanyl’s intended use is to essentially reduce chronic pain, typically for people who may have just had some form of surgery or who are undergoing treatment for cancer.

This prescription medication works by binding to the body’s opioid receptors, which are found in areas of the brain that control pain and emotions. When fentanyl binds to these receptors, it can drive up dopamine levels in the brain’s reward areas, producing a state of euphoria and relaxation. This is the main reason why fentanyl abuse has become more prevalent.

Why is Fentanyl So Dangerous?

Fentanyl is extremely dangerous because it’s extremely potent and addictive, easy to overdose on, and it’s often mixed with other drugs without people knowing. It’s also difficult to detect. These factors make it a significant risk to anyone who uses it or comes into contact with it.

Fentanyl is roughly 50 to 100 times stronger than morphine, which is another potent synthetic opioid used to manage pain. So, what this means is that even a tiny amount of fentanyl can have a very strong effect on the body, with as little as 2mg being enough to cause a fatal overdose.

Because it is such a strong substance, it’s not only incredibly addictive, but it’s also easy to take too much by accident. When someone takes too much fentanyl, it can slow down their breathing to the point where they stop breathing completely. This can happen very quickly, and it can be deadly.

Fentanyl is also dangerous because it is often mixed with other drugs without people knowing. This means someone might take fentanyl without realising it, which increases the risk of a fentanyl overdose.

It’s hard to detect because it doesn’t have much of a smell or taste, and it can be laced with other drugs without the user knowing – making it difficult to know when it is present. This makes accidental overdoses more likely.

How Long Does Fentanyl Stay in Your System?

The detection times and windows for fentanyl can also vary based on the type of drug test used, which can either be a hair, blood, saliva or urine test.

  • Urine tests: Fentanyl can be detected in urine for up to 72 hours after the last use. However, in cases of heavy or chronic use, it may be detectable for even longer.
  • Blood tests: Blood tests have a shorter detection window, usually around 24 hours after the last use.
  • Saliva tests: You can trace fentanyl for up to 48 hours using a saliva test.
  • Hair tests: Hair tests have the longest detection window and can detect fentanyl for up to three months after the last use. This method can show a pattern of drug use over time, but it’s not as useful for detecting recent substance abuse.

Why Knowing the Duration Matters

From a medical safety perspective, for patients who are prescribed fentanyl, knowing how long the drug stays in their system can help prevent accidental overdoses. It also helps medical professionals avoid dangerous interactions with other medications (such as other opioids, benzodiazepines and some anti-depressants).

Also, in addiction treatment, for those struggling with fentanyl addiction, understanding how long the drug stays in their system can help with planning a structured detox period and treatment strategies.

Factors Influencing Fentanyl’s Duration in the System

How long the user can feel fentanyl’s effects will depend on how much is taken, individual characteristics and whether or not it was mixed with other opioids.

The length of time fentanyl remains detectable in the body, however, also depends on several factors:

  • How much they took: Higher doses and more frequent use can prolong the time fentanyl stays in the system.
  • Their metabolism: People with faster metabolisms will process fentanyl more quickly.
  • Their body mass: Individuals with higher body mass or body fat may store fentanyl for a longer period, as it is lipophilic (fat-soluble).
  • Overall health: Overall health, liver and kidney function, and hydration levels can affect how quickly fentanyl is metabolised and eliminated from the body.
  • Age: Older individuals may process drugs more slowly than younger people due to decreased organ function.

What Are the Some Common Signs of Fentanyl Use?

When someone uses fentanyl, they might feel very happy or “high” (euphoria). They can also become very sleepy or drowsy.

Some other signs are feeling sick to their stomach (nausea), feeling very confused, and having trouble going to the bathroom (constipation). Fentanyl can also make a person feel very calm or sleepy (sedation) and can make it hard for them to breathe (respiratory depression).

How Do You Know If Someone Is Overdosing on Fentanyl?

If someone has taken fentanyl and is showing all of the signs mentioned above, as well as having cold but sweaty skin, small pupils, a blueish tinge to their lips and is in and out of consciousness or cannot be woken up at all, they are likely overdosing.

A fentanyl overdose is an emergency. If you suspect someone is overdosing, act quickly:

  • Call an ambulance immediately. Provide as much information as possible, including the person’s condition and any known substance use.
  • Administer naloxone: If it’s available, administer naloxone (Narcan). This medication can temporarily reverse the effects of an opioid overdose. It is available in many areas without a prescription.
  • Perform CPR: If the person is not breathing or has no pulse, perform CPR until an ambulance arrives.

Can Fentanyl Addiction Be Treated?

Yes, but fentanyl addiction is serious. This is especially true if the individual has a history that involves chronic and prolonged use.

Treating fentanyl addiction requires an intensive and comprehensive addiction treatment approach, which will typically involve staying as an inpatient within a clinical setting and includes:

  • Fentanyl detoxification: Medical supervision is often necessary to manage withdrawal symptoms, which can be severe.
  • Medication-assisted treatment (MAT): Medications such as methadone, buprenorphine, and naltrexone can help reduce cravings and withdrawal symptoms.
  • Intensive, ongoing therapy: Behavioural therapies, including cognitive-behavioural therapy (CBT) and contingency management, can help address the underlying psychological aspects of addiction.
  • Ongoing Support Groups: Groups like Narcotics Anonymous (NA) provide peer support and can be an important part of recovery.

Find Fentanyl Addiction Treatment Today

We hope you’ve found this blog useful. And if you or someone you care about is currently abusing Fentanyl, we can support you in finding the best addiction treatment options for you. If you need help, get in touch with the team today.


  • [1] as little as 2mg being enough to cause a fatal overdose -
  • [2] depend on how much is taken, individual characteristics and whether or not it was mixed with other opioids -