In treating pain, codeine works by mimicking the action of naturally occurring pain-reducing chemicals called endorphins. Endorphins are found in the brain and spinal cord and reduce pain by combining with opioid receptors. Codeine mimics the action of natural endorphins by combining with the opioid receptors in the brain and spinal cord. This blocks the transmission of pain signals sent by the nerves to the brain. Therefore, even though the cause of the pain may remain, less pain is actually felt.
With diarrhoea, codeine works by acting on opioid receptors that are found in the muscles lining the walls of the intestines. This reduces the muscular contractions of the intestine (called peristalsis) that move food and faecal matter through the gut. The speed at which the gut contents are pushed through the intestines is therefore reduced, allowing more time for water and electrolytes to be reabsorbed from the gut contents back into the body. This results in firmer stools that are passed less frequently.
Always take codeine exactly as stated on the label of the pack. You should check with your doctor or pharmacist if you are not sure.
Do not take more than the recommended dose.
Do not take for longer than your doctor tells you to.
Swallow the tablets whole with a drink of water.
You can take codeine either before or after food, but taking the tablets after food can help prevent feelings of sickness which can occur with the first few doses.
If you forget to take a dose, take it as soon as you remember and then continue taking your doses every four hours if needed, as before. Do not take two doses together to make up for a forgotten dose.
The usual dose of codeine is one or two 30mg tablets, taken together. Wait at least 4 hours before taking another dose.
Do not take more than 8 tablets of 30mg in any 24-hour period.
Elderly people may be prescribed a lower dose.
If you take more codeine than you should, immediate medical advice should be sought, even if you feel well, because of the risk of delayed, serious liver damage. Remember to take any remaining tablets and the pack with you. This is so the doctor knows what you have taken.
As with all medicines, codeine can cause side effects, although not everybody gets them. The following side effects may happen with this medicine:
Important side-effects you should know about codeine:
- Taking a painkiller for headaches too often or for too long can make them worse.
- Taking codeine regularly for a long time can lead to addiction, which might cause you to experience withdrawal symptoms such as restlessness and irritability when you stop the tablets.
Stop taking codeine and see a doctor or go to a hospital straight away if:
- You get swelling of the hands, feet, ankles, face, lips or throat which may cause difficulty in swallowing or breathing.
- You could also notice an itchy, lumpy rash (hives) or nettle rash (urticaria). This may mean you are having an allergic reaction to codeine.
Talk to your doctor straight away if you notice the following serious side effect:
- Severe stomach pain, which may reach through to your back. This could be a sign of inflammation of the pancreas (pancreatitis). This is a very rare side effect, it affects less than 1 in 10,000 people.
Tell your doctor or pharmacist if any of the following side effects gets serious or lasts longer than a few days:
- Feeling sick (nausea), being sick (vomiting).
- Dizziness, light-headedness, drowsiness, confusion.
- Difficulty in passing water.
- Becoming dependent on codeine.
- You get infections or bruise more easily than usual. This could be because of a blood problem (such as agranulocytosis, neutropenia or thrombocytopenia).
Codeine/dihydrocodeine should only be taken for short periods as it can lead to dependence and in some cases addiction. You must take the lowest dose that controls your pain and never take more than the daily recommended amount. If you believe you need to take it for a longer period we would expect you to have discussed this with your General Practitioner.
Codeine should be used with caution in:
- Elderly people
- People with decreased kidney or liver function
- People with reduced lung function e.g. asthma
- People with a condition called bronchiectasis, in which there is persistent widening of the airways as a result of lung disease, e.g. infection, inflammation, tumours or cystic fibrosis.
- People with biliary tract disorders, e.g. gallstones or recent surgery on the biliary tract.
- People with acute abdominal conditions such as appendicitis.
- People who have recently had surgery on the stomach, intestines or urinary tract.
- People who are constipated.
- People with inflammatory bowel disorders such as Crohn's disease or ulcerative colitis.
- People who have difficulty passing urine, for example men with an enlarged prostate gland (prostatic hypertrophy).
- People with an underactive thyroid gland (hypothyroidism).
- People with underactive adrenal glands, e.g. Addison's disease.
- People with low blood pressure (hypotension) or shock.
- A condition involving abnormal muscle weakness called myasthenia gravis.
- People with a history of convulsions or fits, e.g. epilepsy.
- People with an irregular heartbeat (arrhythmia).
- People with a history of drug abuse or dependence.
Codeine should NOT be used in:
- People who are known to have a genetic variation of a liver enzyme called CYP2D6, which metabolises codeine into morphine (CYP2D6 ultra-rapid metabolisers). These people are more likely to experience side effects after taking codeine, because they convert more codeine into morphine than other people.
- People with very slow, shallow breathing (respiratory depression).
- Chronic obstructive pulmonary disease (COPD).
- People having an asthma attack.
- People who are intoxicated with alcohol.
- Liver failure.
- People who have or are at risk of getting a blockage in the gut (paralytic ileus).
- People with a head injury or raised pressure inside the skull (intracranial pressure).
Codeine should not be used if you are allergic to one or any of its ingredients. Please inform your doctor or pharmacist if you have previously experienced such an allergy. If you feel you have experienced an allergic reaction, stop using this medicine and inform your doctor or pharmacist immediately.
The patient information leaflet (PIL) is a leaflet containing specific information about medical conditions, doses and side effects. You can download a copy of the PIL here:
Patient Info Leaflet