A weak opioid painkiller
Codeine
A weak opioid used for short-term pain that has not settled with simpler painkillers — effective for many people, but with the constipation, drowsiness and dependence risks common to opioids.
What is Codeine?
Codeine is a weak opioid painkiller used for pain that has not responded well enough to paracetamol or anti-inflammatories. It is taken on its own or combined with paracetamol, and is also used in some cough and diarrhoea preparations.
Education and reference only. This is a plain-language guide to Codeine — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Codeine is a weak opioid painkiller used for pain that has not responded well enough to paracetamol or anti-inflammatories. It is often taken on its own but is also very widely combined with paracetamol in a single tablet (co-codamol). It is mainly intended for short-term use in moderate pain, and sometimes for cough or diarrhoea, but its place is increasingly limited as the risks of opioids — particularly dependence and the variable way different people respond to it — have become better understood.
How it works
Codeine is itself only weakly active; the body converts part of it in the liver into morphine, which is what actually relieves pain by acting on opioid receptors in the brain and spinal cord. These receptors dampen the perception of pain, but the same action causes drowsiness, slows the bowel (constipation) and, in larger amounts, slows breathing. The conversion step depends on an enzyme called CYP2D6, which varies a lot between individuals — so the same medicine can give one person strong pain relief and another person almost none.
Company & origin
Originated / developed by: No single originator (first isolated by Pierre-Jean Robiquet, France).
Codeine is a naturally occurring opium alkaloid first isolated in 1832 by the French chemist Pierre-Jean Robiquet. As a classic natural compound it has no single originating pharmaceutical company and is produced generically (largely semisynthetically from morphine).
Practical use
How to take Codeine
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it only as prescribed and for as short a time as possible, as it can become habit-forming.
- Never give to a child under 12, and avoid while breastfeeding.
- Constipation is very common, so increase fluids and fibre, and ask about a laxative if needed.
- It can cause drowsiness, so do not drive or operate machinery until you know how it affects you, and avoid alcohol.
- Do not take it with other opioid medicines or strong sedatives unless specifically advised, because of the risk of dangerous over-sedation.
- Do not stop a long course abruptly; reduce gradually with advice to avoid withdrawal symptoms.
- If you miss a dose, take it when you remember unless the next is nearly due; do not double up.
Weighing it up
Advantages & disadvantages of Codeine
Advantages
- Useful step up for moderate pain when simpler painkillers are not enough.
- Often combined with paracetamol for added effect.
- Also helpful for some types of cough and diarrhoea.
- Taken by mouth and widely available on prescription.
Disadvantages
- Can lead to tolerance, dependence and addiction, especially with prolonged use.
- Commonly causes constipation and drowsiness.
- People process codeine differently, so its effect and safety can vary unpredictably between individuals.
- Must not be used in children under 12, in breastfeeding mothers, or in people known to be ultra-rapid metabolisers, because dangerous amounts of morphine can build up.
- Dangerous if combined with other opioids, sedatives or alcohol, and not suitable for breastfeeding mothers or young children.
Practical use
Good to know
Codeine is best thought of as a short-term medicine: using it for more than a few days at a time risks tolerance (needing more for the same effect) and dependence. Constipation is almost universal, so many people are advised to take a laxative alongside it, and it commonly causes drowsiness, so do not drive until you know how it affects you. Avoid combining it with alcohol or other sedating or opioid medicines, as the effects on breathing and alertness add up. Because of the unpredictable CYP2D6 conversion, it is not used in children or while breastfeeding.
Who should not take it / use with caution
- Children, and women who are breastfeeding — because unpredictable conversion to morphine can lead to dangerously high levels in a child.
- People with breathing problems such as significant respiratory depression or an acute asthma attack, and people with a paralysed or obstructed bowel.
- Used with great caution alongside other opioids, sedatives, sleeping tablets or alcohol, and in anyone with a history of dependence on opioids or other substances.
Monitoring
- No routine blood tests
- Review of how long it is being used, with a plan to stop, to avoid tolerance and dependence
- Bowel habit and alertness, especially in older people
Side effects
- Constipation (very common — often needs a laxative), nausea and drowsiness.
- Dizziness, dry mouth and, with regular use, tolerance and physical dependence.
- In larger amounts or in sensitive people, slowed and shallow breathing — a serious effect that is the main danger in overdose, especially when combined with other sedating medicines or alcohol.
Key interactions
- It adds to the sedating and breathing-slowing effects of other opioids, benzodiazepines, sleeping tablets, gabapentinoids, alcohol and some antihistamines.
- Medicines that block the CYP2D6 enzyme (such as some antidepressants) can reduce how much pain relief it gives, while a few interactions can increase it.
- Care alongside other constipating medicines and with anything else that causes drowsiness.
Available as: Tablets, oral solution (liquid) and, in some settings, an injection. It is also very commonly supplied combined with paracetamol as co-codamol tablets, capsules or effervescent tablets.
Answers
Codeine: frequently asked questions
Why does codeine cause so much constipation?
Opioids slow down the muscle activity of the bowel, so stool moves through more slowly and becomes harder. This is one of the most predictable opioid effects and rarely wears off with time, which is why a laxative is often recommended from the start. Drinking plenty of fluids and staying active helps too — speak to your pharmacist about a suitable laxative.
Why does codeine work well for some people but not others?
Codeine has to be converted in the liver into morphine to relieve pain, and the enzyme that does this (CYP2D6) varies between people. Some convert very little and get almost no benefit, while a few convert a lot and are more prone to side effects. This individual variation is a key reason codeine is unpredictable and is avoided in children.
Can I become dependent on codeine?
Yes — codeine is an opioid, and using it regularly for more than a short period can lead to tolerance and physical dependence, even at intended amounts. It is meant for short-term use. If you find you are taking it more often or for longer than planned, talk to your GP or pharmacist, who can help you reduce it safely rather than stopping abruptly.
Can I drink alcohol while taking codeine?
It is best not to. Both alcohol and codeine slow the brain and breathing, and together the effect is greater and potentially dangerous, with more drowsiness and a higher risk of slowed breathing. Avoid alcohol while you are taking it, and do not combine codeine with other sedating or opioid medicines unless a prescriber has advised it.
What is co-codamol and how does it relate to codeine?
Co-codamol is a combination tablet containing codeine and paracetamol together, so you get two painkillers in one. The codeine part carries the opioid cautions described here — constipation, drowsiness and dependence — while the paracetamol part adds its own. The same advice about short-term use and avoiding extra paracetamol from other products applies.
The wider class
About Opioid analgesics
Codeine belongs to the opioid analgesics class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF: Codeine phosphate.
- electronic Medicines Compendium (SmPC): Codeine phosphate.
- NICE CKS: Codeine.
- MHRA: Codeine - restrictions on use in children and breastfeeding.
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