Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Opioid Analgesia

Codeine Phosphate

Brand names: Codeine Linctus, Codeine Phosphate Tablets

Codeine phosphate is an oral opioid analgesic and prodrug of morphine, used for moderate pain in gynaecology and the postnatal period when simple analgesics are insufficient.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It is metabolised by CYP2D6 to morphine, which acts on central mu-opioid receptors to reduce pain perception; metabolic conversion varies widely between individuals.

Prescribing in practice

  • Codeine is contraindicated in breastfeeding because ultra-rapid metabolisers can produce high morphine levels in breast milk, risking serious neonatal sedation and respiratory depression.
  • Use towards the end of pregnancy and during labour can cause neonatal respiratory depression and, with prolonged use, neonatal withdrawal.
  • Avoid in known CYP2D6 ultra-rapid metabolisers and use the lowest effective dose for the shortest time.

Monitoring

Monitor for analgesic efficacy, constipation, sedation and signs of dependence, and assess the breastfed infant for drowsiness or feeding difficulty if exposure has occurred.

Counselling the patient

  • Do not breastfeed while taking codeine unless specifically advised by a clinician.
  • Expect constipation and consider preventive measures.
  • Avoid alcohol and do not drive if drowsy.

Evidence & guidelines

The MHRA advises against codeine in breastfeeding and restricts paediatric use following reports of serious harm linked to ultra-rapid CYP2D6 metabolism.

Reference: MHRA Drug Safety Update (2013) Codeine; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators