Opioid pain medicines

Also called opioid analgesics or opiates

Opioid pain medicines are used to treat moderate to severe pain, such as after an operation or a serious injury, or pain from cancer. They are used when other weaker pain medicines do not work. Opioids are not recommended for the treatment of chronic (ongoing) pain that is not from cancer.

Key points

  1. Opioids are pain medicines that are used to relieve moderate to severe acute or short-term pain; for example, after an operation or a serious injury. They are also used to treat pain caused by a terminal illness such as cancer.
  2. Opioids are prescribed when weaker pain medicines alone don't work well enough. See pain relief medications and opioids in palliative care
  3. Opioids are not recommended for the treatment of chronic (ongoing) pain, that is not related to cancer because it's not very effective for this type of pain and there are side effects, including addiction. Read more about chronic pain.

Opioids work by binding to certain receptors in your brain and spinal cord which decreases pain and your reaction to pain, and it increases your tolerance for pain. 

Examples of opioids available in New Zealand

Opioids are divided into 2 groups.

Weak opioids Strong opioids

These opioids are available in different formulations such as a liquid or syrup, quick-acting tablets and capsules, slow-release tablets and capsules, patches to put on your skin, or injections, which may be under your skin, into a vein or into a muscle.

Which opioid is best for me?

In New Zealand, opioids are available only on prescription. Your doctor will discuss the best option for you. There are many things that affect the choice of opioids, including:

  • intensity of your pain: the weaker opioids such as codeine or dihydrocodeine are best for moderate pain, while the stronger opioids are used for more severe pain. The strong opioids differ a lot in strength; some of them are 10 times stronger than weaker opioids. 
  • type of pain: quick acting tablets and capsules or liquids start working quickly to ease pain and are useful to treat sudden pain. Slow-release tablets and skin patches release the medicine slowly over several hours to give more even pain control. They are used when continuous pain relief is required.  Injections may be used when tablets, capsules or liquids cannot be taken or if immediate pain relief is needed.  

How to take opioids safely

Opioids are strong medication with good pain relief but may cause harm including dependence and addiction. Here are a few tips on how to use opioids safely.

Repeat doses

  • Follow the instructions on the pharmacy label carefully.
  • Do not increase your dose or take doses more often than prescribed without talking to your doctor first.
  • Sometimes you may feel pain before you have your next dose is due. It's important to tell your doctor this so that your dose can be changed, or another pain relief option can be considered.
  • One problem with opioids is that they can become less effective with time. This is called tolerance. It means that your body has got used to the pain-relieving effect of the medicine, so you will need more to get the same effect. This is why it is important for your doctor you know exactly what dose you are taking. 


  • Opioids can cause drowsiness and confusion and affect your ability to concentrate.  You are more likely to feel drowsy at the start of treatment and when you have a dose increase.
  • It's best not to drive if you have just started taking an opioid, or if the dose has been recently increased. 
  • Once you are settled on the dose and if you do not have any side effects that might affect your driving, you may be able to return to driving.


  • Drinking alcohol as well as taking an opioid may increase drowsiness, especially at the start of treatment or when the dose is being increased. It is better to avoid alcohol if you are taking an opioid, or to drink less alcohol than usual.
  • This is of concern if you drive or operate machinery.

Stopping opioids

  • Do not stop taking your opioids suddenly. You may have withdrawal symptoms if you stop them or lower the dose too quickly. 
  • Withdrawal symptoms include tiredness, sweating, diarrhoea, restlessness and irritability.
  • To avoid this, your doctor will reduce your dose gradually. 

What about side effects?

As with all medicines, opioids can cause side effects, although not everyone gets them. Common side effects include: 

Side effects What should I do?
  • Feeling sleepy, dizzy or tired
  • Reduced concentration
  • This is common when starting opioids or after increasing the dose.
  • Be careful when driving or using tools until you know how this medicine affects you.
  • Feeling sick (nausea) or vomiting
  • This common in the first week to 10 days of treatment.
  • Mostly this settles and goes away.
  • Tell your doctor if this is a problem. You may need an anti-sickness tablet.
  • Constipation
  • Constipation is  quite common.
  • Ask your doctor to prescribe a laxative; you will need to take it on a regular basis.
  • You also need to eat more fruit, vegetables, brown bread, wholegrains, bran based breakfast cereals and drink plenty of water.

Addiction to opioids

Addiction is an excessive craving. If you are addicted, it means you are not able to control your use of opioids. It is unusual for people who are prescribed opioids for pain to become addicted to opioids. However, some people are more likely to develop addiction than others and seem to be very sensitive to the cravings. People who are addicted can still have cravings for opioids even after they have reduced them slowly and are no longer dependent on them. You may be at risk for addiction if you have mental health problems such as depression or a history of substance abuse, including alcohol and recreational drugs.

Learn more

The following links provide further information about opioids. Be aware that websites from other countries may have information that differs from New Zealand recommendations.

Understanding morphine and other opioid medicine Palliative Outcome Initiative, 2019
Strong painkillers opioids Patient Info, UK, 2016


  1. Opioids Health Quality and Safety Commission, New Zealand
  2. Opioid analgesics New Zealand Formulary
  3. Strong opioids for pain management in adults in palliative care BPAC, December 2012, NZ
  4. Helping patients cope with chronic non-malignant pain: it’s not about opioids BPAC, September 2014, NZ  
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 02 Dec 2019