Side effects of opioid painkillers

Like all medicines, opioid painkillers can cause side effects. We explain the common side effects.

Opioid painkillers, such as morphine or oxycodone, are used to treat pancreatic cancer pain. Like all medicines, opioids can cause side effects. We describe the most common side effects here, but you may not get all or any of these. Some side effects settle down within a few days of starting a new drug. Other side effects may last longer.

Speak to your doctor or nurse if you have any side effects. It may not always be clear what is causing them because the cancer can sometimes cause similar symptoms. Your doctor may change or lower the dose of your painkillers. Or they may give you a different opioid drug or another type of pain relief. Speak to our specialist nurses on our free Support Line about opioids and side effects.


Opioids can cause constipation, which is problems emptying your bowels. Fentanyl may be less likely to cause constipation than morphine.

Your doctor or nurse may give you medicines, called laxatives, to prevent or treat constipation. If you are taking a stronger opioid like morphine, you may need to start taking a laxative straight away – your doctor can advise you about this. It can also help to drink lots of water and try to keep active if possible.

''We found that including things like prune juice or syrup of figs into his diet helped with constipation.’’

Sickness and dry mouth

Opioids can make you feel and be sick (nausea and vomiting). This usually gets better after two to five days as your body gets used to your painkillers, but it can last longer for some people.

Your doctor or nurse can give you medicine to prevent sickness. They may change the type of painkiller you are using if your sickness continues.

You may also get a dry mouth. Some people find that drinking plenty of water, sucking ice cubes or chewing gum helps.

Read more about dealing with sickness

‘We found pineapple juice and frozen pineapple were good to help a dry mouth, and ice lollies helped with a fresher taste.’’


Another common side effect of opioids is tiredness. You may also feel dizzy or have trouble concentrating. You may have this when you first start taking a new opioid, or when you change the dose. Drinking alcohol can make tiredness worse. The tiredness will usually go away within a day or two as you get used to your painkillers.

Tiredness and trouble concentrating can affect your driving.

Tiredness may not just be caused by your painkillers. Extreme tiredness is known as fatigue. It can be caused by the cancer itself, or your symptoms or treatment.

Read more about fatigue and pancreatic cancer.

Other side effects

Other possible side effects of opioid painkillers include:

  • mood changes or feeling confused
  • sensing things that aren’t there (hallucinations)
  • itchy skin
  • problems emptying your bladder completely
  • muscle twitches or jerks.

Questions about painkillers and side effects?

Speak to your doctor or nurse if you have any of these side effects, especially if you have recently changed your pain medicine. They may change the dose of your painkiller, or give you a different painkiller.

You can also speak to our specialist nurses on our free Support Line.

Speak to our nurses
A specialist nurse taking a phone call.

Updated February 2019

To be reviewed February 2021