Opioid medicines overview

Also called opioid analgesics or opiates

Opioid pain medicines are used to treat moderate to severe short-term pain, such as after an operation or serious injury, or ongoing pain from cancer.

Key points

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

Examples of opioids available in NZ

Opioids are divided into 2 groups, weak and strong opioids.

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.

Opioids and chronic non-cancer pain

Opioids should not be the first medicine you try for pain relief, if you have chronic (ongoing) non-cancer pain. It is important to explore other treatment options such as lifestyle changes, self-management skills and other medicines. Read more about chronic pain

The following video provides information to people who may be considering taking opioids for chronic (ongoing) non-cancer pain. This video is not for people taking opioids for cancer pain or palliative care.

(NPS MedicineWise, Australia, 2020)

Which opioid is best for me?

Opioids are best used to help manage short-term pain, cancer pain or palliative care.  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 the intensity and type of pain.

  • 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.  

Read more about opioids in palliative care.

How to take opioids safely

Opioids are strong medication with good pain relief but may cause harm including dependence. 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 your next dose is due. Tell your doctor this so your dose can be changed or another pain relief option can be considered.
  • Opioids 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 your doctor needs to 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.
  • This effect is of concern if you drive or operate machinery.
  • It's better to avoid alcohol if you are taking an opioid or to drink less alcohol than usual.

Stopping opioids

  • Don't 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. 

Note: In this video, Dr Mike Evans mentions some opioid medicines that are not available in New Zealand, such as Percocet, Vicodin, Dilaudid, and many statistics that are relevant to the United States. However, much of the video is still relevant to New Zealanders.

(Dr Mike Evans, US, 2013) 

What are the side effects of opioids?

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

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 and bran-based breakfast cereals and drink plenty of water.
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product


When someone is dependent on their opioid medicine, they will experience withdrawal symptoms if the opioid dose is reduced or stopped. Dependence can occur within 1 month of starting to take an opioid.

For some people, the main reason they continue to take opioids long term is to avoid withdrawal symptoms, although they may not realise this. They mistakenly think the opioid is working to reduce pain, when in fact it’s only reducing withdrawal symptoms, which can include pain.

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, NZ
Managing non-cancer pain with opioid medicines Choosing Wisely, NZ 
Strong painkillers opioids Patient Info, UK
Risks of opioid medicines Medsafe, NZ


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