In this information, we use the general (generic) name of each drug, rather than the brand name.
There are different types of opioid painkillers, including weaker and stronger opioids. They may be taken in different ways, and have different side effects. You may take them with other types of pain relief. The type of painkiller you have will depend on what kind of pain you have, and your general health.
If you have been taking opioids for a long time, you must not stop taking them suddenly. This can cause severe symptoms like stomach pains, sickness and feeling worried or restless. Your doctor or nurse will help you to slowly reduce the dose so that you don’t get these symptoms.
Weaker opioids include codeine, dihydrocodeine and tramadol. You may have a weaker opioid if your pain isn’t controlled by paracetamol or NSAIDs.
You may take a weaker opioid on its own, or with other drugs. If you still have pain, tell your doctor or nurse so that they can change the dose or painkiller.
If weaker opioids do not control your pain, you may have a stronger opioid. Your doctor or nurse will work out the best dose for you that manages your pain, without causing bad side effects. You will usually start on a lower dose of a stronger opioid. The dose can be increased, so let your doctor or nurse know if you still have any pain.
Stronger opioids include morphine, oxycodone, fentanyl, buprenorphine, methadone and tapentadol.
Some stronger opioids are available in two forms:
Fast acting opioids (immediate release) start to work after about 20 minutes and reach full effect after about an hour. This makes them good for treating breakthrough pain or sudden changes in pain.
You may start off with a fast acting opioid.
You usually take a long acting opioid (modified release) twice a day to control background pain. These opioids take longer to have the full effect. So you must take them regularly at the same time of day for them to work properly. Sometimes you may take a fast acting dose and a long acting dose at the same time. This will give you pain relief straight away, followed by the effect of the long acting medicine.
Like all medicines, opioids can cause side effects. We explain the most common side effects here, but you may not get all or any of these. Ask your doctor or nurse about possible side effects. Some side effects settle down within a few days of starting a new drug. Others 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 the dose of your painkillers. Or they may give you a different opioid drug or another type of pain relief.
Opioids can cause constipation, which is when you find it harder to poo.
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 plenty 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.”
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 will give you medicine to prevent sickness. They may change the type of painkiller if your sickness continues.
You may also get a dry mouth. Some people find that drinking water, sucking ice cubes or chewing gum helps and there are also artificial saliva gels and sprays. If you have white spots in your mouth or a white coating on your tongue, you may have an oral thrush infection. Your doctor can give you medicine to treat this.
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. The tiredness will usually go away within a day or two as you get used to your painkillers.
Drinking alcohol can make tiredness worse. Tiredness and trouble concentrating can affect your driving.
Tiredness may not just be caused by your painkillers. The cancer and treatment can cause extreme tiredness (fatigue).
Other possible side effects include:
Speak to your doctor or nurse if you have any of these side effects, especially if you have recently changed your painkiller. They may change the dose, or give you a different painkiller.
Ask our specialist nurses on our Support Line any questions about opioids and side effects.
Updated April 2022
To be reviewed April 2025
