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Side effects of painkillers

There can be side effects to painkillers used to treat cancer pain. You may not get them, but it helps to know what they could be.

Morphine type drugs

Morphine type drugs (called opioids) can cause:

  • constipation
  • feeling sick
  • dry mouth
  • itchy skin
  • blurred vision
  • difficulty passing urine

As with any drug, you will not necessarily get all these side effects. Constipation and sickness are the most common. There’s information on controlling them further down this page.

The dose of the drug is too high if you have any of these effects:

  • drowsiness
  • spidery lines at the edge of your vision
  • unusually vivid dreams
  • hallucinations
  • shaking or muscle twitching or jerks
  • confusion
  • feeling agitated
  • painful and sensitive skin all over your body

Your doctor or nurse will slightly lower the dose and these effects should go. If the lower dose affects your pain control, they’ll suggest that you change to a different painkiller.

Tell your doctor if you’ve been taking morphine type painkillers for some time and start to get drowsy or feel that you’re sleeping too much. You might need a lower dose of the drug or a different type of painkiller.

This is particularly likely if you've had some treatment to shrink your cancer that has helped to relieve your pain. It can also happen if you get dehydrated, so it’s important to drink plenty of fluids.


All morphine type drugs cause constipation. This can be quite painful if it isn't treated. It can continue for the whole time that you’re taking strong painkillers.

Your doctor or nurse will prescribe stool softeners or laxatives as soon as you start taking painkillers. It is important to take them regularly.

Other ways that you can help prevent constipation include:

  • drinking plenty of fluids, especially water
  • increasing the amount of fibre you have in your diet, from fruit, vegetables and grains such as bran
  • moving around as much as you can – but don't wear yourself out or make your pain worse


Morphine type drugs can make you feel sick. Some people actually are sick.

Many doctors give an anti sickness drug with these painkillers for the first week or so. This stops you feeling sick. Once you get used to your painkillers, you can stop taking the anti sickness drugs. But if the sickness doesn't go away, you’ll need to carry on taking them.

Anti inflammatory drugs

Anti inflammatory drugs can irritate your stomach and bowel (digestive system). They can cause stomach bleeding or ulcers if you take them without anything to protect your stomach.

They can also slow down the time your blood takes to clot. So if you have any bleeding or clotting problems, your doctor may not use these drugs.

Some types of anti inflammatory drugs can also affect the ways your kidneys work.


You might feel worried when you look at the side effect list in your packet of steroids. The list does look long.

But many of the effects are unlikely to happen unless you’ve been taking steroids for some time. And they’ll go away when you stop taking the steroids.

Your doctor will give you a card to carry to say that you’re taking steroids. This is because it’s important for any doctor treating you (for any reason) to know this. Carry the card with you at all times, in case of emergencies.

The most likely side effects when you first start taking steroids are:

  • having more of an appetite
  • having more energy
  • difficulty sleeping
  • indigestion

Try taking your steroids early in the day if you’re having trouble sleeping.

Your doctor will probably prescribe something to help prevent indigestion and to stop the steroids from irritating your stomach. Even so, it’s best not to take steroids on an empty stomach.

If you’ve been taking steroids for some time

You might notice some swelling in your hands, feet or eyelids if you’ve been taking steroids for some time. You may also put on weight. Steroids can cause water retention. It is the extra fluid in your body that causes swelling and weight gain.

Other side effects

Your doctor or nurse will be looking out for other side effects of your steroids. These are:

  • raised blood pressure
  • increased risk of infection
  • raised blood sugar
  • sugar in your urine
  • loss of strength in muscles

You may be asked to test your urine for sugar. Or your nurse may ask you to take urine samples to the hospital for testing.

Because your resistance to infection is lowered, it's best to avoid people with obvious infections while you are taking steroids.

Remember that it is very important not to stop taking steroids suddenly, because this can make you very ill. When you stop taking them, your doctor or nurse will explain how to reduce the dose gradually.

Anti epileptic drugs

Drugs that prevent fits can also have side effects. Depending on the drug, these can include:

  • difficulty sleeping
  • tiredness
  • dizziness
  • loss of appetite
  • feeling sick

This is a very general list. Ask your doctor to tell you more about the side effects of the drugs that you’re taking.

Anti depressants

Different anti depressants have different side effects. They can cause: 

  • a dry mouth
  • an increase or decrease in appetite
  • changes to your sleep pattern
  • drowsiness

The specific effects depend on which drug you take. Ask your doctor or nurse for advice on the specific side effects of your drug.


Bisphosphonates can cause sickness or diarrhoea in some people. One or two of these drugs may also cause tiredness, muscle aches or a skin rash.

With the drug clodronate (Bonefos or Loron), it’s better not to eat or drink milk for an hour before or after taking it. Milk reduces the amount of clodronate absorbed by the body. And don’t take iron tablets, other mineral supplements or antacids while you’re taking clodronate. These also reduce the absorption of the drug from your digestive system.


Denosumab (Xgeva) is a type of drug called a monoclonal antibody.

Doctors might use it to treat pain caused by cancer that has spread to the bones. It may also help to prevent fractures and other bone problems caused by cancer that has spread to the bones.

Information and help

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