Fentanyl | Cancer Research UK
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What fentanyl is

Fentanyl is a type of opioid painkiller. It treats moderate to severe long term (chronic) cancer pain. It can also help to control breakthrough cancer pain. Breakthrough pain is pain that occurs despite taking regular painkillers for long term pain. 

Breakthrough pain can happen suddenly and can be very severe. It might be caused by movement or activities such as walking, changing position, or coughing. It can also be unexpected and happen for no apparent reason. Some types of fentanyl work very quickly and work very well for this type of pain.


How fentanyl works

As an opioid, fentanyl works by mimicking the body’s natural painkillers, endorphins. These control pain by blocking pain messages to the brain. 

Find out about cancer and pain control


How you use fentanyl

You can only get fentanyl on prescription from a doctor. Your dose of fentanyl will be specific to you and depends on the amount you need to control your pain. Your doctor or nurse will give you instructions on how much to have and when to have it. You can have fentanyl in different ways.


Fentanyl patches

The brand names of fentanyl patches include Durogesic DTrans, Tilofyl and FENCINO. They are for long term cancer pain. You stick a fentanyl patch on your skin and the drug is absorbed into your body over a period of time. Doctors call this a transdermal system.

The best areas to put the patches are on the inner part of your upper arm, the top of your chest, or on your back. To make sure that you get the dose of fentanyl that you need, find an area of skin that is

  • Clean and dry
  • Not too hairy – you can cut the hair but shouldn’t shave the area
  • Not irritated or sore
  • Not a previous radiotherapy site
  • Flat and not likely to wrinkle when you move
  • Has no creams, soap or lotions on it

All of these can change how you absorb the drug so you may absorb more or less.

You will need to have another type of painkiller when you put the first patch on. The patches take a while to reach the correct dose at first, and won’t work fully for 24 hours. They usually last for 72 hours (3 days). When you need to change a patch, put the new one on a different area of skin. Your skin can get sore or itchy if you keep putting them in the same place. Don't forget to take off the old patch.

When you open the packet you need to be careful not to damage the patch, so don’t use scissors. When you stick the patch onto your skin, press hard for about 30 seconds with the palm of your hand. Make sure that it has stuck, especially around the edges.

The patch can loosen and might not work so well when it is hot or you are sweating a lot. If it becomes loose, you may need to stick some tape over the patch. If it becomes a problem, talk to your nurse or doctor. Tell them if you have a high temperature (fever) because this can sometimes increase the amount of fentanyl you absorb. Don’t put any direct heat on the patch, such as a hot water bottle, because this can also increase the amount you absorb.

Remember that when you remove the patch it can take 24 hours for the effects of the drug to wear off.


Fentanyl lolly (lozenge)

The brand name for this lozenge on a stick is Actiq. It gives fast pain relief. You suck the lozenge and move it around your mouth so that it is in contact with the mouth lining. You might have it to relieve any pain that you get between doses of other painkillers. This is known as breakthrough pain. 

You usually suck the lolly for about 15 minutes. It should start to control pain within 5 minutes and work fully within 30 minutes. You must not bite, chew or swallow the lozenge. 


Fentanyl tablets

The brand names are Abstral or Effentora. Fentanyl tablets give fast relief of pain. You might have them to relieve any pain that you get between doses of other painkillers (breakthrough pain). You put the tablet under your tongue and it dissolves. It usually starts to control pain within 5 minutes and works fully within 30 minutes.


Fentanyl square to fit inside your cheek

The brand name is Breakyl. It is a small dissolvable square that you fit into the side of your cheek. The dissolvable square is called a buccal film. One side is pink and the other side is white. The pink side contains fentanyl.  It gives fast relief of pain. 

You use your tongue to wet the inside of your cheek. Or you can rinse your mouth with water. Then with dry hands you put the square into your mouth so that the pink side is in contact with the inner lining of your cheek. You need to press and hold it in place for a minimum of 5 seconds until it sticks firmly. Then the square should stay in place on its own. It usually dissolves completely within 15 to 30 minutes.

After 5 minutes you can drink liquids. But you shouldn't eat food until the square has completely dissolved. You also need to avoid moving the square with your fingers or tongue. You mustn't chew or swallow the square as then it won't work properly in controlling the pain. 


Nasal spray

The brand names are Instanyl and PecFent. You spray the liquid up your nose and it is absorbed from the nasal lining. It gives very fast pain relief and works about 5 minutes more quickly than fentanyl lollies or tablets. It can be very helpful in giving quick pain relief to people who have nausea or vomiting, a very sore or dry mouth, or who can't swallow.


About side effects

We've listed the side effects associated with fentanyl. You can use the links to find out more about each side effect. Where there is no link, please go to our information about cancer drug side effects or use the search box at the top of the page.

You might have a few side effects. They may be mild or more severe. A side effect may get better or worse through your course of treatment. Or more side effects may develop as the course goes on. This depends on

  • How many times you've had the drug before
  • Your general health
  • The amount of the drug you have (the dose)

The side effects may be different if you are having fentanyl with other medicines.

Tell your doctor, nurse or pharmacist straight away if any of the side effects get severe.


Common side effects

More than 10 in every 100 people have one or more of these.

  • Constipation – to prevent this, try to drink at least 2 litres of fluid, eat at least 5 portions of fruit and vegetables a day, and ask your doctor or nurse if you should have a laxative. Contact your doctor or nurse if you have a change in your normal bowel movements for more than a few days
  • Feeling or being sick – this usually wears off after a few days, but tell your doctor or nurse if it continues. You might need an anti sickness drug at first
  • Tummy pain – let your doctor or nurse know if you have this
  • Drowsiness might be a problem at first or when you increase the dose but it usually wears off after a few days
  • Dizziness
  • Headaches
  • Breathlessness
  • Weakness

Occasional side effects

Between 1 and 10 in every 100 people have one or more of these.

  • A dry mouth
  • Mood changes – you might feel very happy or very sad
  • Confusion
  • Anxiety
  • A low sex drive (libido)
  • A skin reaction (with the fentanyl patches) – your skin might be red for a day or so after removing a patch
  • Feeling generally unwell
  • Muscle jerks
  • A feeling of spinning, tingling or numbness
  • Increased sensitivity to touch
  • Difficulty coordinating movements
  • Taste changes
  • Seeing or hearing things that are not there (hallucinations)
  • Wind and a bloated tummy
  • Indigestion
  • Loss of appetite
  • Sweating
  • A skin rash – let your doctor or nurse know if you have this
  • Difficulty passing urine

Rare side effects

Fewer than 1 in 100 people have these.

  • Slowing of the heart beat or palpitations – tell your doctor or nurse because you might need a lower dose of fentanyl
  • Blurred vision or double vision
  • A drop in blood pressure that makes you feel dizzy or light headed
  • Mouth ulcers (with fentanyl lozenges)
  • Abnormal dreams and feeling detached from reality
  • An overwhelming feeling of wellbeing
  • Extreme drowsiness and inability to respond
  • Loss of consciousness

Important points to remember

Coping with side effects

Talk to your doctor, pharmacist or nurse about any side effects so they can help you manage them. They can give you advice or reassure you. Your nurse will give you a contact number to ring if you have any questions or problems. If in doubt, call them.

Drowsiness or slow breathing

Fentanyl can slow your breathing or make you very sleepy if the dose is too high. If you have these effects tell your doctor or nurse straight away and call another person nearby to stay with you.

Other medicines, foods and drinks

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies. Some drugs can react together.

Don't drink grapefruit juice while having fentanyl, as it can change the way the drug is broken down in the body.

Don't drink alcohol while using fentanyl because it can increase the drowsiness and other side effects.

Pregnancy and contraception

This drug might harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having this drug and for a few days afterwards. Talk to your doctor or nurse about effective contraception while you are having fentanyl.


Don't breastfeed while having fentanyl or for 48 hours afterwards because the drug might come through in the breast milk.

Driving and using machinery

Don't use machinery or drive if you feel dizzy, drowsy, or sleepy or if you have blurred vision or difficulty concentrating.

Sugars and fentanyl

Some fentanyl lozenges and tablets contain types of sugar called glucose or sucrose. If you have diabetes, you need to take this into account. The sugars can also harm your teeth. Make sure you clean your teeth regularly. 

Worries about addiction

Because fentanyl is an opioid, some people worry about becoming addicted. When you take an opioid to control pain, you are very unlikely to become addicted. The body uses the drug to control pain, not to make you feel high. You can read about fear of addiction.


More information on fentanyl

This page doesn't list all the very rare side effects of this treatment that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at www.medicines.org.uk.

If you have a side effect not mentioned here that you think may be due to this treatment you can report it to the Medicines Health and Regulatory Authority (MHRA) at yellowcard.mhra.gov.uk.

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Updated: 4 May 2016