Opioid Analgesic (Weak) Pregnancy: Caution during pregnancy, especially first trimester; possible association with respiratory and cardiac malformations after first-trimester exposure. Regular use may cause fetal drug dependence and neonatal withdrawal. Administration during labour may depress neonatal respiration. Breast-feeding: not recommended (secreted in breast milk; may cause infant respiratory depression) — codeine is contraindicated during breastfeeding.

Codeine Phosphate

Brand names: Codeine (generic)

Codeine phosphate is a weak opioid analgesic used for mild-to-moderate pain and, at lower doses, as an antitussive and antidiarrhoeal.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Mild to moderate pain: lowest effective dose, up to 4 times a day at intervals of not less than 6 hours

Route: Oral

Frequency: Up to 4 times a day at intervals of not less than 6 hours

Max: 240 mg codeine daily

Pain: use at the lowest effective dose for the shortest period; duration of treatment limited to 3 days — if no effective relief, seek a physician. Dry or painful cough (adults): 15-30 mg three to four times daily. Diarrhoea (adults): 30 mg three to four times daily (range 15-60 mg). Elderly: dosage should be reduced. Avoid or reduce dose in renal or hepatic impairment. Contraindicated in children under 12 years (risk of opioid toxicity from variable CYP2D6 metabolism) and in CYP2D6 ultra-rapid metabolisers. Contraindicated in all paediatric patients (0-18 years) undergoing tonsillectomy/adenoidectomy for obstructive sleep apnoea. Discuss a treatment-ending strategy before starting (addiction/withdrawal risk).

Dose adjustments

Renal

Avoid or reduce dose in patients with renal impairment

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Acute respiratory depression; obstructive airways disease
Hypersensitivity to codeine or other opioid analgesics or to any excipient
Liver disease / severe hepatic dysfunction; acute alcoholism
Raised intracranial pressure or head injury; comatose patients
Conditions where inhibition of peristalsis is to be avoided (risk of paralytic ileus, abdominal distension) or acute diarrhoeal conditions (e.g. ulcerative colitis, antibiotic-associated/pseudomembranous colitis, diarrhoea caused by poisoning); all paediatric patients (0-18 yrs) undergoing tonsillectomy/adenoidectomy for OSA; breastfeeding women; known CYP2D6 ultra-rapid metabolisers

Side effects

Drowsiness, dizziness, headache; nausea, vomiting, constipation, dry mouth
Postural hypotension, facial flushing; tachycardia, palpitations, bradycardia
Respiratory depression (large doses); dyspnoea
Urinary retention, difficulty with micturition; miosis; blurred/double vision
Addiction and tolerance with regular prolonged use; drug withdrawal syndrome

Interactions

Monoamine oxidase inhibitors (MAOIs) — administration of pethidine and possibly other opioid analgesics to patients taking a MAOI has been associated with reactions
CYP2D6 metabolism — deficiency reduces analgesic effect; ultra-rapid/extensive metabolisers at increased risk of opioid toxicity
Other CNS depressants — caution (opioid class effect)

Clinical monograph

How it works

Codeine is a prodrug metabolised by CYP2D6 to morphine, which acts as a mu-opioid receptor agonist to produce analgesia; some direct opioid effect also contributes.

Prescribing in practice

Ultra-rapid CYP2D6 metabolisers convert codeine to morphine excessively; it is contraindicated in breastfeeding mothers and in children under twelve, and is not recommended after tonsillectomy/adenoidectomy in under-18s with obstructive sleep apnoea, owing to fatal respiratory depression.
It carries the usual opioid risks of respiratory depression, dependence, tolerance and constipation, with additive sedation alongside other CNS depressants.
Efficacy is unpredictable as CYP2D6 poor metabolisers gain little analgesia while CYP2D6 inhibitors reduce conversion to morphine.

Monitoring

Monitor pain control, sedation, respiratory status and bowel function, and review for signs of dependence with prolonged use.

Counselling the patient

Do not exceed the prescribed dose and avoid combining with alcohol or other sedating medicines.
Take a laxative or increase fibre and fluids if constipation occurs.
Breastfeeding mothers should not use it; seek advice about excessive drowsiness in the infant.

Evidence & guidelines

The MHRA has restricted codeine use in children and breastfeeding women because of the risk of morphine toxicity in ultra-rapid metabolisers.

Reference: MHRA Drug Safety Update Nov 2013; WHO Pain Ladder; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

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