Codeine — Pain Relief Guide | KiwiMeds
✅ Reviewed by a Registered Pharmacist NZ | Last updated: May 2026 | This information is for educational purposes only and does not replace advice from your doctor or pharmacist.
What is codeine?
Codeine is a mild opioid pain reliever and cough suppressant. In New Zealand, codeine-containing products are available on prescription and in some over-the-counter combination products (e.g., with paracetamol). Note that since 2020, NZ has made pure codeine products prescription-only; codeine-paracetamol combinations at low doses can still be purchased over the counter from pharmacists.
What is it used for? (NZ context)
Codeine is used for mild-to-moderate pain and as a cough suppressant. In NZ it is commonly combined with paracetamol (e.g., Panadeine, Codalgin). For pain relief, it is generally used for short-term management when paracetamol or ibuprofen alone is insufficient.
How does it work?
Codeine is a prodrug — it is converted to morphine in the body by the liver enzyme CYP2D6. Morphine then binds to opioid receptors in the brain and spinal cord, reducing pain perception and suppressing cough. About 5–10% of people are poor metabolisers of codeine (CYP2D6) and get little pain relief.
How to take it
Take exactly as directed. Do not exceed the recommended dose. Use for the shortest time necessary — opioids carry a risk of dependence. Take with food if stomach upset occurs. Paracetamol-codeine combinations must be taken carefully to avoid accidental paracetamol overdose if combined with other paracetamol products.
Common side effects
- Constipation — very common
- Nausea and vomiting
- Drowsiness
- Dizziness
- Itching (histamine release)
Serious side effects to watch for
In rare “ultra-rapid metabolisers” (particularly children), codeine is converted to morphine very quickly causing potentially dangerous opioid toxicity. Codeine is not recommended for children under 12 or people under 18 following certain surgeries. Signs of opioid overdose: severe drowsiness, slow breathing, confusion — seek emergency help immediately.
Important drug interactions
Other sedatives, opioids, benzodiazepines, and alcohol — significantly increased sedation and respiratory depression risk. CYP2D6 inhibitors (e.g., fluoxetine, paroxetine) — may block codeine conversion to morphine, reducing effectiveness. Serotonin syndrome risk with certain antidepressants.
NZ-specific information
Pharmac funding: Prescription-only codeine 30mg tablets are funded by Pharmac. Low-dose codeine-paracetamol combination products (8mg codeine/500mg paracetamol) can be purchased without a prescription from a pharmacist in NZ, following pharmacist oversight.
Frequently asked questions
Can I buy codeine over the counter in NZ?
Low-dose codeine-paracetamol combinations (e.g., Panadeine) can be purchased from a pharmacist without a prescription, but the pharmacist is required to discuss your use. Pure codeine or higher-dose products require a prescription.
Why does codeine make you constipated?
Opioids including codeine slow down bowel movements by reducing gut motility. Constipation affects most people who take codeine. Drink plenty of water, eat fibre-rich foods, and consider a laxative (such as lactulose) if using codeine for more than a few days.
Is codeine addictive?
Yes — codeine carries a risk of dependence and misuse, especially with prolonged use. It should only be used for short-term pain relief. If you find yourself needing increasing amounts or feeling unable to stop, speak to your pharmacist or doctor.
💬 Talk to your pharmacist or doctor for personalised advice about codeine.
Reviewed by a Registered Pharmacist NZ | BPharm, Pharmacy Council of New Zealand
References & Further Information
The following New Zealand and international resources were used to inform this page: