Fentanyl: What You Need to Know

Medically Reviewed by Jabeen Begum, MD on June 05, 2024
12 min read

Fentanyl is a human-made opioid used to treat severe pain. It's 50 to 100 times stronger than morphine. The drug interacts with receptors in your brain to create feelings of pain relief, relaxation, contentment, and pleasure.

While it’s safe for your doctor to give you fentanyl in a medical setting, some people abuse it, which can lead to an overdose.

Where does fentanyl come from?

Fentanyl is in a class of drugs called opioids. Opioids come from the opium poppy plant. While some opioids come directly from the plant, fentanyl is made in a lab by scientists using the same chemical structure.

People sell illegal fentanyl as a powder, dropped onto blotter paper, put in eye droppers and nasal sprays, or as pills that look like other prescription opioids.

Fentanyl can also be “diverted.” That's when the drug is prescribed by a doctor but isn't used as directed or is sold or given to someone else.

A sharp increase in deaths from illegal fentanyl use started in 2005 and continued through 2007. Again in 2011, both deaths from illegal fentanyl use and police encounters with illegal fentanyl use rose significantly. 

This overdose rate has continued to rise in part because fentanyl is often mixed into or sold as other drugs. Because fentanyl is so strong, it takes only a small dose of the drug to cause death. 

Your doctor might prescribe fentanyl if you have severe pain due to cancer, nerve damage, serious injury, or major surgery.

Before giving you fentanyl, your doctor should ensure that you’re not allergic to it or to any other narcotic pain medications. Tell your doctor if you’ve ever had:


  • Sleep apnea
  • Breathing problems
  • A brain tumor
  • A head injury
  • A stroke
  • Seizures
  • Liver or kidney disease
  • Slow heartbeats or other heart problems
  • Low blood pressure
  • Mental illness, such as depression or schizophrenia
  • Hallucinations

Also, tell your doctor if:

  • You’ve used an antidepressant called a MAO inhibitor (isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, tranylcypromine) in the last 14 days
  • You’re pregnant, plan to become pregnant, or are breastfeeding

Fentanyl typically comes either as a powder or a liquid. When it’s in powdered form, it looks a lot like other powdered drugs such as cocaine. Powdered fentanyl can also be pressed into pills that look like prescription pills such as Percocet or Xanax.

Rainbow fentanyl

This more recent version of fentanyl comes in bright colors. People who make it mix it with dyes and either press it into multicolored pills or sell it in a colored powder form. 

Drug enforcers theorize that dyes may help drug traffickers avoid detection with the drugs. They speculate that it may also be a way to tempt teens and young adults to take them. The claim that some of the colors have a stronger effect than others is a myth. Lab tests show that this isn't true. 

Medical fentanyl comes in many forms, including:

  • Lozenges, sometimes on a stick (Actiq)
  • Skin patches (Fentora)
  • As an injection or through an IV (Sublimaze) 
  • Tablets that dissolve under your tongue (Abstral)
  • Mouth sprays (Subsys)
  • Nasal sprays (Lazanda)

The drug can be manufactured illegally. Dealers may sell it as a standalone drug or as a counterfeit for another drug (like oxycodone). It's also used as a low-cost additive to other drugs like heroin, methamphetamine, molly, and ecstasy.

When people take fentanyl illegally, they may take it by:

  • Smoking or snorting it in powder form
  • Injecting the liquid form
  • Swallowing the powder in pressed pill or tablet form
  • Putting drops on blotter paper and putting it on their tongue
  • Spraying the liquid form into their nose
  • Dropping the liquid form in their eyes
  • Sucking on candies made with it

Fentanyl patch

Although fentanyl patches are a legal form of the drug doctors sometimes prescribe for pain, they are easily abused. People may take the gel out of the patch and either put it in their mouth or inject it.

Some people take fentanyl illegally by separating it from skin patches and injecting it. This can be dangerous since it’s hard to judge dose size. You could inject a lot more fentanyl than you thought.

Sometimes people freeze fentanyl patches and cut them into smaller portions. Then they put these small pieces in their cheeks or under their tongue. 

Fentanyl patches pose a danger to kids who can stick them on their skin or mouths. This can cause death by slowing their breathing and lowering oxygen levels in their blood.

Fentanyl acts like many other opioids such as morphine and heroin. It works by changing the way the brain and nervous system respond to pain.

Short-term effects

The “high” that people feel from fentanyl causes effects such as:

  • Relaxation
  • Euphoria
  • Pain relief 
  • Feeling of calm

Fentanyl side effects

After a fentanyl treatment, you may have side effects that hinder your thinking and reactions or cause dizziness or drowsiness. Because of this, don't drive or do activities that require you to be fully alert and awake after your treatment. Avoid drinking alcohol for several hours after you take fentanyl.

Fentanyl may cause other side effects. Let your doctor know if any of these symptoms don’t go away or become serious:

  • Drowsiness
  • Stomach pain or heartburn
  • Weight loss
  • Trouble peeing
  • Vision changes
  • Anxiety or depression
  • Unusual thinking or dreams
  • Trouble falling or staying asleep
  • Dry mouth
  • Sudden reddening of your face, neck, or upper chest
  • Shaking in any part of your body
  • Back or chest pain
  • Mouth pain, sores, or irritation in the location where you were given fentanyl
  • Swelling in your hands, feet, arms, ankles, or lower legs

Call your doctor right away if you notice:

  • Changes in your heartbeat
  • Hallucinations, agitation, fever, sweating, confusion, shivering, muscle stiffness or twitches, loss of coordination, nausea, vomiting, or diarrhea
  • Loss of appetite, weakness, or dizziness
  • Sexual or menstrual problems
  • Seizures
  • Hives or rashes
  • Itching

Call 911 and stop using fentanyl if you have:

  • Shallow, slow breathing
  • Trouble swallowing and breathing
  • Intense drowsiness
  • Dizziness or confusion
  • Fainting

Fentanyl long-term effects

After you’ve taken an opioid like fentanyl for a long time, your brain gets used to the drug. This means your tolerance goes up and it takes more of it to get the same effect. You also have trouble feeling pleasure from anything besides the drug. 

Over time, using fentanyl may also cause:

  • Unstable mood
  • Reduced libido
  • Constipation
  • Problems with your menstrual cycle
  • Breathing problems

How long does fentanyl stay in your system?

This drug stays in your system for 24-72 hours. This means a drug test would detect it up to about 72 hours after you’ve taken it. 

Prescription fentanyl can work for various amounts of time depending on how you take it. Tablets, lozenges, and nasal sprays take about 15 to 30 minutes to work but wear off after 4 to 6 hours.

Fentanyl patches can take up to 2 days to start working, but they last longer. 

Fentanyl is not only much stronger than other opioids, but it’s often added to illicit drugs without people knowing. People making illegal fentanyl often do this because it’s less expensive to use fentanyl than other drugs.  

This means that someone who has never taken fentanyl may take it thinking they’re taking a different opioid, but their body isn’t used to the drug. This makes it much more likely for overdose to happen. 

The U.S. Drug Enforcement Administration estimates more than 258,000 people died from fentanyl overdose between 2013 and 2021. 

Can you unknowingly take fentanyl?

Yes. You can’t smell or taste fentanyl. Because the drug is less expensive than other opioids, people making it illegally commonly mix it into drugs such as heroin, cocaine, or methamphetamines. If you buy drugs illegally, there is a chance fentanyl can be in them. 

Lethal dose of fentanyl

It’s hard to predict the amount of fentanyl that could kill someone. As little as 2 milligrams may be lethal depending on how big your body is, what your tolerance for opioids is, and your past usage of fentanyl.

There is always a risk when you use opioids. But these tips can reduce some of that risk and lower your chances of overdose, infection, or other problem. 

  • Have an overdose plan so friends and family know what to do if it happens.
  • If you haven’t used fentanyl, start with very small doses.
  • Carry naloxone (Narcan) with you and tell others you have it.
  • Don’t use when you’re alone. If you don’t have anyone with you and are planning to take fentanyl, you can call Never Use Alone (877-696-1996).
  • Don’t use fentanyl with other drugs or alcohol.
  • If you’re injecting fentanyl, don’t use a needle someone else has used, and don’t share your needle with anyone. Make sure your injection site and syringe are both clean. Syringe services programs are available in many cities to help people with access to clean supplies.
  • Take care of your overall health. Dehydration, lack of sleep, and hunger can increase your risk of overdose.
  • Test any drugs you’re taking for the presence of fentanyl. 


Mixing fentanyl with any drug is risky, but some drugs pose a serious danger if you take them alongside fentanyl. You should never take fentanyl with:

  • Amphetamines. You can strain your heart and go into respiratory arrest
  • Nitrous oxide. This can keep you from controlling your muscles well, sedate you, and lead to unconsciousness.
  • Alcohol/benzodiazepines/ketamine. You’re at a high risk of becoming unconscious and dying. You can also easily choke on vomit. 

Fentanyl test strips

To prevent accidental fentanyl overdoses, you can use fentanyl test strips to ensure other drugs don’t contain the opioid. You can get them free through some outreach programs, such as needle exchanges or overdose prevention programs.

Test strips can’t tell you how much fentanyl there is, what kind it is, or how pure it is. To use test strips, you:

  • Put a small amount of crushed, crystal, or powdered form of a drug in a container.
  • Add about 1/4 inch of water. (Testing MDMA or methamphetamine requires slightly more water.)
  • Insert the fentanyl test strip into the water and hold for 15 seconds.
  • Take the strip out and lay flat for 3 minutes.

One line is a positive result and means there is fentanyl in your drug supply. Don’t use this drug. Two lines is a negative result. 

Fentanyl is very addictive. It's one of the most common drugs involved in overdose deaths. You can become dependent on fentanyl even if you’re taking it as directed by a doctor. This means you’ll experience withdrawal symptoms once you stop taking it. Dependence can lead to addiction.

You can treat drug addiction with medication and behavioral therapy. Medications for opioid addiction work on the brain by interacting with the same receptors that opioids affect and causing different effects. These drugs include:

  • Buprenorphine
  • Methadone
  • Naltrexone

Counseling can help you learn new behavioral patterns, stick with medication use, and reroute your thinking pathways. Some types of therapy that can help treat drug addiction include:

  • Cognitive behavioral therapy (CBT), which helps you alter expectations, manage triggers, and reduce stress
  • Contingency management, which is a voucher-based system that gives you “points” based on negative drug tests
  • Motivational interviewing, which addresses the way you approach change in your life

Once you’ve been taking fentanyl for a while, your body gets used to it and stopping can be very hard. It can be hard to function without the drug in your system. Most people need help from a health professional or program to successfully quit. 

Withdrawal symptoms typically start within 12 hours after your last dose of the drug. They can last for about a week. The first 3 days are the hardest, with the most severe symptoms. 

Fentanyl withdrawal symptoms

Typical symptoms that happen when your body is adjusting to the absence of fentanyl include:

  • Goosebumps
  • Cycling through periods of chills and excessive sweating 
  • Irritability
  • Insomnia
  • Loss of appetite
  • Yawning and sneezing
  • Watery eyes and runny nose
  • Vomiting and nausea
  • Diarrhea
  • Increased heart rate and blood pressure
  • Bone and muscle pain
  • General weakness
  • Depression

An overdose happens when a drug produces serious adverse effects and life-threatening symptoms. When people overdose on fentanyl, their breathing can slow or stop. This can decrease the amount of oxygen that reaches the brain, a condition called hypoxia. Hypoxia can lead to a coma, permanent brain damage, and even death.

If you unknowingly take fentanyl in another drug, you may overdose since fentanyl is so potent.

Call an ambulance right away if you suspect you or someone you're with may have taken an overdose.

Fentanyl overdose symptoms

Signs of an overdose can show up within seconds of taking fentanyl. They include:

  • Blue lips and complexion
  • Gurgling or slow breathing
  • Chest pain
  • Seizure or stiffening of the body
  • Confusion or strange behavior
  • Passing out

What to do if you think someone is overdosing

If you suspect someone is overdosing on fentanyl, call 911 immediately. Many people worry that calling emergency services for someone taking an illegal drug will get them in trouble, but this is not true. Many states have laws that protect not only the person who calls for help, but also the person overdosing from legal trouble. 

You should also:

  • Give the person naloxone if you have it. You don't have to be a health care professional to give this medication. You can get it from a pharmacist without a prescription. It comes in a fast-acting nasal spray or a preloaded multiple-dose syringe. Some experts recommend having naloxone on hand whenever someone in the household is taking narcotics.
  • Try to keep them awake and breathing.
  • Turn them on their side so they don’t choke.
  • Stay with them until the paramedics arrive. 

First responders will likely administer naloxone if you haven’t already, or give it to them again. Naloxone only works in the body for 30 to 90 minutes, so it’s possible for someone to still have overdose effects after the medication wears off or needs multiple doses.

  • Fentanyl is a human-made opioid used to treat severe pain. It's 50 to 100 times stronger than morphine
  • Fentanyl overdose rates have continued to rise, in part because fentanyl is often mixed into or sold as other drugs. 
  • Because fentanyl is so strong, it takes only a small dose of the drug to cause death.

Is fentanyl an opioid?  Yes, scientists consider fentanyl an opioid. Some opioids come directly from the opium poppy plant, but manufacturers make fentanyl in a lab and reproduce the chemical structure.

What does fentanyl do to you? Fentanyl changes the way your nervous system and brain respond to pain. Doctors prescribe it to help treat pain.

How does fentanyl make you feel? Fentanyl typically relaxes you and puts you in a euphoric state. It relieves pain and can make you feel calm. You may also feel dizzy, drowsy, have vision changes, or have unpleasant side effects such as dry mouth, stomach pain, or anxiety. 

How long does fentanyl stay in urine? Fentanyl stays in your system and can be detected by a drug test for 24 to 72 hours. 

How much fentanyl can kill you? There is no set amount that is considered lethal because how the drug affects you depends on several factors such as your body size and tolerance. As little as 2 milligrams or less may cause death, which is about the size of a few grains of salt. 

What is fentanyl made from? Manufacturers use chemicals to make a substance with the same chemical structure as poppies to make fentanyl in a lab.