Codeine

• The dose of codeine is different for different people. 
• Always take codeine exactly as your doctor has told you.
• Depending on the reason you are taking codeine, your doctor may advise you to take regular doses or take it only when you need it for relief. Make sure you know how you are to take it.
• The pharmacy label on your medicine will tell you how much codeine to take, how often to take it and any special instructions.

Variations in response to codeine

Codeine is broken down in your liver to morphine, which is a strong pain reliever. People may respond differently to codeine depending on how their liver breaks down codeine.

• Some people are poor metabolisers, which means that they are unable to convert codeine to morphine, and don't get enough pain relief.
• Some other people break down codeine very quickly (ultra-rapid metabolisers) and are at increased risk of developing side effects, even at low doses.
• Estimates suggest that up to 10% of the European/Pākehā population may be poor or ultra-rapid metabolisers. The prevalence in Māori and Pasifika people is not known.
• If you are taking codeine for pain relief, and it doesn’t seem to be working, let your doctor know.
• If you are taking codeine and get side effects such as nausea, vomiting, constipation, lack of appetite, drowsiness or extreme sleepiness, let your doctor know. Other options may be better for you. 
• If you have more severe side effects, such as difficulty waking, confusion or shallow breathing, let your doctor know straight away or call Healthline 0800 611 116.

• You can take codeine with or without food.
• Stop taking codeine if your symptoms are relieved. 
• Limit or avoid drinking alcohol while you are taking codeine. Combining codeine with alcohol can make you sleepy, drowsy or dizzy.

• Are you pregnant or breastfeeding?
• Do you have problems with your liver or your kidneys?
• Do you have problems with your prostate or any difficulties passing urine (peeing)?
• Do you have any breathing problems, such as asthma or chronic obstructive pulmonary disease (COPD)?
• Have you had a recent head injury?
• Do you suffer from constipation, eg, constipated for more than a week?
• Do you have an inflammatory bowel problem?
• Have you ever been dependent on drugs or alcohol?

If so, it’s important that you tell your doctor or pharmacist before you start codeine. Sometimes a medicine isn’t suitable for a person with certain conditions, or it can only be used with extra care.

Here are some things to know when you're taking codeine. Other things may be important as well, so ask your healthcare provider what you should know about.

• Other medicines: Codeine may interact with a few medicines and herbal supplements, so check with your doctor or pharmacist before starting codeine or before starting any new medicines. It may interact with medicines available without a prescription such as:
  • cough suppressants (eg, Benadryl Dry Forte®, Duro-Tuss®)
  • sedating antihistamines (eg, Phenergan®).

Like all medicines, codeine can cause side effects, although not everyone gets them. Often side effects improve as your body gets used to the new medicine.

Addiction

Addiction is an excessive craving. If you are addicted to codeine, it means you are not able to control your use of it. It is unusual for people who are prescribed codeine for short periods of time to become addicted to it.

Some people are more likely to develop addiction than others. 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.

To reduce your risk of addiction, codeine should be used for the shortest possible time, at the lowest effective dose, with a plan in place to reduce and withdraw treatment.

Other side effects