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

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.

Fentanyl is not available over the counter. You can only get it with a prescription from your doctor.

Fentanyl is also called:

  • Abstral
  • Actiq
  • Durogesic DTrans
  • PecFent
  • Effentora
  • Matrifen

How does fentanyl work?

Fentanyl is a type of opioid. Opioids are strong drugs similar to natural pain killing substances made in our body called endorphins. 

Opioids block pain messages from travelling along the nerves to the brain. 

How do you have fentanyl?

You can have fentanyl in different ways including:

  • patches 
  • lollies (lozenges)
  • tablets that dissolve under your tongue or between the gum and the cheek
  • nasal spray 

You should apply a fentanyl patch on a flat part of your upper body or arm. For example, the inner part of your upper arm, the top of your chest, or on your back. 

To make sure that you get the right dose of fentanyl, 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. Do not put the patch on a joint.
  • has no creams, soap or lotions on it

The patches take a while to reach the correct dose at first. So you might need to have another type of painkiller when you put the first patch on. The drug is absorbed slowly into your body over a period of time. Each patch usually lasts 72 hours (3 days). 

Putting a patch on

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.

When you need to change the patch, first take off the old patch. Then put the new one on a different area of skin. Your skin can get sore or itchy if you keep putting the patches in the same place. 

The patches are usually waterproof, so you can shower and bathe while wearing them. But you shouldn't scrub them. The patch can loosen and might not work so well when it is hot or you are sweating a lot. You shouldn't put any direct heat on the patch, such as a hot water bottle. If it becomes loose, you may need to stick some tape over the patch.

Don’t sit right next to or very near a heat source such as a radiator or heat lamp as this can increase how much fentanyl is absorbed into the body. And this can increase the side effects.

Fentanyl lozenges give 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. And always keep fentanyl lozenges out of sight and reach of children. 

You might have fentanyl as tablets that dissolve under your tongue (sublingual). Or as tablets that dissolve between your gum and cheek (buccal). 

Dissolvable tablets give fast relief of pain. So you might have them to relieve any pain that you get between doses of other painkillers (breakthrough pain). It usually starts to control pain within 5 minutes and works fully within 30 minutes.

Taking the tablets

If your mouth is dry, take a sip of water to moisten it. Spit out or swallow the water. Then place the tablet as far back under your tongue or between your gum and cheek. The tablet starts to dissolve straight away. 

You shouldn't chew or swallow the tablet as it won't work properly. You can eat and drink normally after the tablet has been completely absorbed. 

The nasal spray gives very fast pain relief. You might have it if you are feeling sick, have a sore month, or if you can't swallow.

Before you apply the spray, blow your nose if you feel the need to. You then spray the liquid up one nostril, while closing the other nostril with a finger. Then breathe in gently through your nose and out through your mouth.

How often do you have fentanyl?

Your healthcare team will help you choose the type and dose of fentanyl that best controls your pain. It depends on the pain you have and the amount of drug you need to control it.

You should always take fentanyl exactly as your healthcare team prescribes it. You shouldn't just stop taking fentanyl. You usually need to slowly reduce the amount you take. Always talk to your doctor or specialist nurse before you change your dose.

What are the side effects of fentanyl?

Side effects can vary from person to person. They also depend on what other treatment you are having. 

When to contact your team

Your doctor, nurse, or pharmacist will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects 

  • your side effects aren’t getting any better

  • your side effects are getting worse

Early treatment can help manage side effects better.

We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.

The side effects you have also depend on how you have fentanyl. 

Common side effects

These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:

Feeling or being sick 

Feeling or being sick is usually well controlled with anti sickness medicines. It might help to avoid fatty or fried foods, eat small meals and snacks and take regular sips of water. Relaxation techniques might also help.

It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treat it once it has started.


Constipation Open a glossary item is easier to sort out if you treat it early. Drink plenty of fluids and eat as much fresh fruit and vegetables as you can. Try to take gentle exercise, such as walking. Tell your healthcare team if you think you are constipated. They can prescribe a laxative.


Drowsiness may be a problem at first or when your dose is increased, but usually wears off after a few days.

 Do not operate machinery or drive if you are feeling drowsy.

Difficulty breathing 

You may have difficulty breathing with wheezing and coughing. Let your healthcare team know straight away if this happens. 

Tummy (abdominal) pain

Tell your treatment team if you have this. They can check the cause and give you medicine to help. 


Tell your healthcare team if you keep getting headaches. They can give you painkillers to help.


You might feel very tired and as though you lack energy.

Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.


This drug might make you feel dizzy. Don’t drive or operate machinery if you have this.

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

  • mouth problems such as a dry mouth and mouth ulcers
  • taste changes
  • loss of appetite and weight loss
  • watery or loose poo (diarrhoea)
  • sweating more than normal
  • confusion and seeing or hearing things that are not there (hallucinations)
  • mood changes such as low mood (depression)
  • difficultly coordinating your movement, feeling like the room is spinning (vertigo) and falling
  • fits (seizures) and loss of consciousness
  • muscle jerks or spasms
  • tingling or pricking in fingers and toes
  • problems with your eyes such as blurred and double vision
  • indigestion or heartburn
  • passing more wind than usual
  • difficulty passing urine and pain when passing urine
  • heart problems such as high blood pressure and a fast or irregular heartbeat
  • skin changes such as rash and redness
  • difficulty sleeping
  • an allergic reaction
  • feeling cold and generally unwell
  • shaking
  • nose bleeds and pain in your nose

Rare side effects

This side effects happens in fewer than 1 in 100 people (fewer than 1%). You might have one or more of them. They include:

  • flu like symptoms and high temperature (fever)
  • difficulty getting an erection
  • slow and shallow breathing
  • feelings of intense happiness or confidence and agitation
  • feeling thirsty
  • a build up of fluid in your body (oedema)
  • loss of memory and personality changes
  • tolerance and addiction to fentanyl which can cause withdrawal symptoms if the drug is stopped
  • pain in different parts of your body such as the throat, stomach, joints and muscles
  • bowel problems such as your bowel may stop working temporarily
  • low blood pressure and a slow heart rate
  • a drop in the number of white blood cells which can increase your risk of having infections
  • loss of fluid in your body (dehydration)
  • high blood sugar levels
  • nightmares and vivid dreams
  • hot flushes

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do you need to know?

Other medicines, foods and drinks

Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Loss of fertility

It is not known whether this treatment affects fertility in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Pregnancy and contraception 

It is unknown whether treatment may or may not harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you are having treatment. Let your team know straight away if you or your partner become pregnant while having treatment.

Talk to your doctor or nurse about effective contraception you can use during treatment. Ask how long you should use it before starting treatment and after treatment has finished.


Don’t breastfeed during this treatment because the drug may come through into your breast milk.

Treatment for other conditions 

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.

Tolerance and addition 

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.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

Related links