Opioids for pain

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Learn why opioids such as morphine, fentanyl and codeine are prescribed and how they help manage pain in children.

Key points

  • Opioids are among the oldest and best-known pain medications.
  • When taken exactly as instructed, opioids are very effective in treating moderate to severe pain with no risk of overdose or addiction.
  • The most commonly used opioids are morphine, oxycodone, hydromorphone, fentanyl and codeine.
  • Opioid side effects include constipation, drowsiness, itching, nausea, vomiting, mood changes and, most seriously, shallow and slow breathing.

Although there are many types, formulations and strengths of opioids, they are all chemically related to the same poppy plant that produces opium. Opioids are either synthetically produced or natural products and are among the oldest and best-known pain medicines.

Some parents have serious concerns about their children being given these opioids. Mostly, they worry about addiction and the possibility of an overdose. However, these drugs are very effective for dealing with moderate to severe pain. And, if they are used properly, they should not pose these risks to the child.

The most commonly used opioids are morphine, oxycodone, hydromorphone, fentanyl and codeine. These pain medicines act on the tissues of the central nervous system and the brain to provide pain relief.

Morphine and other opioids

Morphine​ and other opioid medicines such as fentanyl​, oxycodone and hydromorphone are among the strongest pain relievers. They are usually prescribed for moderate to severe pain and are frequently used following surgery, for cancer pain, and when ongoing pain relief is needed.


Codeine only works because it is converted into morphine by an enzyme in the liver. However, up to 30% of children genetically do not have this enzyme. For them, codeine will have no effect on their pain. The opposite genetic condition also exists for some people. Called “codeine ultrametabolizers” these children convert codeine into excessive amounts of morphine which can be dangerous. It is possible that a child with this very rare condition could suffer a morphine overdose. The good news is now that this condition has been identified, health-care providers can monitor a child for dangerous side effects when first given codeine. Knowledge of this condition also means that some health-care providers may choose to use a different type of opioid to avoid this small risk.

Although it continues to be prescribed elsewhere, codeine and all codeine-containing medicines have been removed from The Hospital for Sick Children since 2010 to eliminate this risk.

Side effects

There are side effects associated with opioids. All opioids slow down the bowels, and cause constipation and hard stools in about 50% of people. Although laxatives are often prescribed to relieve constipation, this is the only side effect that tends not to improve over time. Your child may require the occasional or regular use of laxatives while taking opioids to help maintain regular bowel movements. Opioids may also cause drowsiness, itchiness, nausea and vomiting. Some children may require additional medications to help control these side effects if they become intolerable. Some children develop an urgency to pee, while others have difficulty peeing. Opioids can also alter a child’s mood. For example, they might feel euphoric or very giddy, or they might feel a little down or teary. Some children may have vivid dreams or mild hallucinations, and feel disoriented. Health-care professionals can provide guidance that will help to minimize the impact of these worrying side effects.

Uncommonly, and if given in too high a dose, opioids can cause low blood pressure or respiratory depression, which is characterized by shallow breathing and a slow breathing rate. Children need to be carefully monitored for these effects as these are the most serious side effects of opioids. There are ways of medically managing serious side effects of opioids.

Should serious opioid-related side effects such as respiratory depression occur, the child may be given an antidote called naloxone that works quickly to reverse the effects of opioids.

If your child is involved in their treatment, share with them the handout Five Questions to Ask About My Medicine. It will help them be better prepared when meeting with their health-care team.

Opioid checklist

​SickKids has developed a checklist for parents and caregivers on the safe use and disposal of opioids. Always speak with your child's health-care team if you have any questions or concerns about your child's opioid prescription.

Last updated: May 16th 2014