Fentanyl

What is fentanyl?

Fentanyl is a very strong synthetic opioid, primarily used for pain management. It is approximately 100 times more potent than morphine and 50 times more potent than heroin[1][2].  

How does fentanyl work?

Fentanyl works by binding to the body's opioid receptors, which are found in areas of the brain that control pain and emotions[2], to block pain signals between the brain and the rest of the body. It can also help to reduce the anxiety and stress brought on by pain[1]. 

What is fentanyl used for?

Fentanyl is used to treat severe pain, particularly in patients who are already tolerant to other opioids[1][3]. It is commonly prescribed for: 

• Breakthrough pain in cancer patients 

• Severe pain during or after an operation or serious injury 

• Long-term pain when weaker painkillers have stopped working. 

Who can take fentanyl?

Most adults can use fentanyl, and some patches can be used by children aged 2 and over, although young children and older people are more likely to experience side effects. 

Fentanyl patches are only used if you’ve been taking other strong opioid painkillers. Your doctor or pharmacist will determine the strength depending on your medical and pharmaceutical history[1]. 

Fentanyl is not suitable for everyone. You should mention the following to your doctor or pharmacist: 

• You are already taking strong opioid painkillers or alternatively if you have not been taking high dose opioids (opioid-naive) 

• You have had an allergic reaction to fentanyl or any other medicine 

• You have breathing difficulties or lung conditions like asthma 

• You are addicted to alcohol or drink heavily 

• You have a head injury 

• You have a condition that causes fits or seizures 

• You have an irregular heartbeat 

• You have adrenal gland, kidney, or liver problems 

• You have an enlarged prostate 

• You have lower pressure 

• You are trying to get pregnant, are pregnant or breastfeeding 

Please tell your doctor or pharmacist about any conditions you may have before starting fentanyl, and always follow the instructions in the Patient Information Leaflet[12].

How do you take fentanyl?

It's important to follow your doctor’s or pharmacist’s instructions about how to use fentanyl as it can be addictive. 

Fentanyl can come in tablets, lozenges, nasal sprays and injections; all formulations work quickly and are designed to be used on pain that’s expected to last for a short time. 

It can also come in patch form, which slowly releases the fentanyl through the skin into your body. It takes longer to work but lasts longer and is designed for chronic or longer-lasting pain. 

Some patches will keep working after they’ve been taken off as they store the fentanyl under the skin[1]. 

What is the typical dosage of fentanyl?

The typical fentanyl dosage depends on the type you take: 

• Patches – Come in several strengths from 12micrograms/hour up to 100micrograms/hour and should be replaced every 72 hours 

• Nasal spray – contains 100micrograms to 400micrograms per dose  

• Tablets – contain 100micrograms to 800micrograms 

• Lozenges – 200micrograms to 1,600micrograms 

It varies from person to person, and will depend on how bad your pain is, how you’ve responded to alternative painkillers and what side effects you experience[1]. 

What to do if you forget to take fentanyl?

Most types of fentanyl are only taken when needed, so you’re unlikely to forget. However, you should never take 2 doses at one time and never have an extra dose to make up for a forgotten one. 

For transdermal patches, apply the missed patch as soon as you remember and continue with your regular 3-day schedule[3][10]. Do not apply extra patches to make up for a missed dose and always remove the old patch before applying the new one. 

What do you do if you take too much fentanyl?

It's hugely important to never take more than the dose you are prescribed, even if you think it won’t help your pain. Speak to your doctor or pharmacist first if you want to change your dose. 

Taking too much fentanyl can be dangerous, but the amount that may lead to an overdose can vary depending on the person. 

If you’ve taken more than your prescribed fentanyl dose, even if you have no symptoms, you should go to 111.nhs.uk or call 111. Call 111 if you’re asking about a child under 5. 

If you’ve taken more than your prescribed fentanyl dose and are having difficulty breathing, starting to lose consciousness or feel sleepy, sick, or dizzy, you should call 999 or go to A&E immediately. You should also do this if you or someone else swallows a fentanyl patch[1]. 

What are the side effects of fentanyl?

The most common side effects of fentanyl will occur in more than 1 in 100 people. These include[1][5][4]: 

• Nausea and vomiting 

• Constipation 

• Drowsiness and dizziness 

• Stomach pain 

• Dry mouth 

• Sweating 

• Confusion 

• Itching or skin rashes 

Serious side effects occur in less than 1 in 100 people and can include[5][4]: 

• Muscle stiffness 

• Dizziness, drowsiness, and/or low energy as a sign of low blood pressure 

• Short, shallow breathing or general respiratory difficulty 

• Fainting or seizures 

• Allergic reactions (rash, itching, swelling) 

In very rare cases, fentanyl can cause a serious allergic reaction, known as anaphylaxis. 

If you experience any of these more serious side effects, stop taking fentanyl and call 999 immediately. 

The information provided in the side effects section is not a comprehensive list of all possible side effects associated with this medication. For a complete list of side effects, please refer to the Patient Information Leaflet (PIL) provided with your medication or consult your healthcare professional.

If you experience any side effects, including those not listed, you are encouraged to report them via the Yellow Card Scheme or contact your doctor, pharmacist, or nurse. This information is intended as a summary for general awareness and does not replace professional medical advice[12].

Medicines you can and can't take with fentanyl

Fentanyl can interact with many medications[11][12]: 

• Avoid: Benzodiazepines, sleep medications, muscle relaxants, and alcohol due to increased risk of respiratory depression[12] 

• Use with caution: Other opioids, certain antidepressants, and medications that affect liver enzymes[11] 

You should tell your doctor or pharmacist if you’re taking any medicines: 

• To help you sleep 

• For high blood pressure 

• For an irregular heartbeat 

• To help stop you feeling or being sick 

• To treat allergy symptoms 

• For mental health problems like depression, stress, and anxiety 

• For any infection (including HIV) 

• To control fits or seizures 

It's safe to take fentanyl with painkillers like paracetamol, ibuprofen, or aspirin, but you should speak to your doctor or pharmacist before you take it with any painkillers containing codeine, including co-codamol, Solpadine, and Nurofen Plus.

Always inform your doctor or pharmacist about all medications and supplements you take before you start a new medicine, and follow the instructions in the Patient Information Leaflet[12]. 

Frequently asked questions about fentanyl

Can fentanyl be addictive? 

Yes, fentanyl is a strong opioid and has a high risk of addiction and dependence[13]. 

Why is fentanyl so dangerous?  

Fentanyl's high potency increases the risk of overdose, especially when misused or combined with other substances[13]. If you have not taken opioids previously or only taken a low dose (known as opioid-naive), fentanyl is not recommended due to risk of side effects including difficulty breathing. 

How long does it take for fentanyl to work? 

It depends on what type of fentanyl you take.  

An injection provides the quickest pain relief, but this is usually only given in hospital.  

Fentanyl lozenges, tablets and nasal sprays take about 15 to 30 minutes to start working but will wear off after 4 to 6 hours. 

Patches can take a day or two to start working, but they’ll last longer. 

Are there long-term side effects to taking fentanyl? 

People who take fentanyl for an extended period can become used to it, meaning you need higher doses to control your pain. In this case, people can become more sensitive to pain, known as hyperalgesia, so your doctor or pharmacist will look to reduce your dose gradually. It is important to reduce analgesia to decrease the risk of side effects and ensure it continues to be effective. 

It is possible to become addicted to fentanyl, so your dose will be reviewed regularly to make sure you’re not taking more than you ever need to. 

How do I know if I’m addicted to fentanyl? 

You’ll find it hard to stop using it or feel like you want to use it more than needed. If you stop taking it suddenly, you may experience withdrawal symptoms including: 

• Anxiety or agitation 

• Panic attacks 

• Heart palpitations 

• Sleeping problems 

• Shaking 

• Sweating 

• Aches 

• Restlessness 

You should talk to your doctor or pharmacist as soon as possible if you’re worried about or need help with addiction, or if you want to stop taking fentanyl altogether. 

What happens if I stop taking fentanyl? 

If you need to take fentanyl for a long time, your body can get used to it and you build up a tolerance. This is not normally a problem, but you can experience withdrawal symptoms (above question) if you stop taking it suddenly. You should talk to your doctor or pharmacist first before coming off fentanyl. 

How long does fentanyl stay in your system? 

Fentanyl can be detected in the body for up to 72 hours after use[14]. 

What should I do if my fentanyl patch falls off? 

Apply a new patch to a different skin site and inform your doctor or pharmacist [10]. 

What do I do with used fentanyl patches? 

You should fold any used patches in half, so the sticky sides stick to each other and then place it back in its packaging. This is so that patches do not accidently end up sticking to another person.  

You should then return any used or any unused patches to your pharmacist who will destroy them for you. 

Does fentanyl affect contraception? 

No, it does not stop any type of contraception from working. 

However, if you vomit due to taking fentanyl, your contraception may not protect you from pregnancy. If this happens, reach out to your doctor or pharmacist for advice. 

Can I drive or ride a bike while taking fentanyl? 

If fentanyl makes you sleepy, gives you blurred vision, or makes you feel dizzy, confused or unable to concentrate, then you should not drive or ride a bike. It's an offence to drive if your ability to drive safely is impacted. 

Do I need to avoid any food or drink, including alcohol, while taking fentanyl? 

You shouldn’t drink while taking fentanyl until you see how the medication affects you. Drinking will make you sleepier and increase the risk of serious side effects. 

You should also avoid drinking grapefruit juice as it can increase the amount of fentanyl in your body.