Codeine phosphate: an opioid painkiller explained

The NHS describes codeine as a strong opioid painkiller prescribed for pain, for example after an operation or an injury, and often when simpler painkillers such as paracetamol and ibuprofen have not worked. It can also be used for a dry or painful cough and for diarrhoea. Those are separate decisions for a prescriber.

There are lower-strength products where codeine is mixed with paracetamol (co-codamol) or with ibuprofen, and these have their own pages. The details here relate to codeine alone.

It comes as tablets or a liquid you swallow. The amount and duration depend on why it has been prescribed, so the NHS says to follow the leaflet and ask a pharmacist or doctor if unsure. Tablets are swallowed whole with half a glass of water, with or without food, and liquids are measured with the syringe or cup supplied.

If a dose is missed, take it when you remember unless the next dose is close, in which case skip it. Do not double up. The NHS warns that an extra dose of codeine can be dangerous, and that if you take more than your prescribed dose you should seek medical help.

Common effects are constipation, feeling or being sick, feeling sleepy or tired, and sweating. If you are sleepy or tired do not drive, ride a bike or use machinery until it passes.

Possible serious effects are an allergic reaction with swelling of the throat or tongue, a raised itchy rash or difficulty breathing; slow, weak or shallow breathing; an unusual heartbeat; and low blood pressure with confusion, blurred vision, weakness, light-headedness or dizziness. Seek urgent help for breathing problems or signs of anaphylaxis.

People who take codeine for a long time become used to it, and the NHS says it is possible to become addicted. Doctors aim to ensure you take only what you need to control pain. Stopping suddenly can cause withdrawal symptoms such as feeling agitated or anxious, so doses are reduced gradually over several weeks or months.

If you are worried about addiction, the NHS advice is to talk to your doctor. Do not change the dose yourself.

The NHS says most adults and children aged 12 and over can take codeine, but it may be unsuitable if you have had an allergic reaction to codeine or another opioid, have a liver or kidney condition, lung problems such as asthma, a past addiction to alcohol, prescription medicines or recreational drugs, an underactive thyroid or adrenal problems such as Addison disease, an enlarged prostate, low blood pressure or a head injury. It is also unsuitable for people under 19 recovering from tonsil or adenoid removal for obstructive sleep apnoea.

Pregnancy: tell your doctor; codeine is sometimes used if needed after a discussion of risks and benefits. Breastfeeding: not usually used, because it could cause side effects in the baby.

The NHS lists other opioid painkillers such as co-codamol, medicines for depression or other mental health conditions, some antihistamines, anti-sickness medicines and other anti-diarrhoea medicines among those that may not mix well. Taking codeine with cannabis, cocaine or heroin raises the risk of serious side effects.

You can eat and drink normally, but it is best not to drink alcohol because it can increase the risk of side effects.