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Weak opioid analgesic

Codeine phosphate

Codeine is a weak opioid for mild-to-moderate pain (also used for cough or diarrhoea in some settings), frequently combined with paracetamol.

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.

US labelling (FDA)

Reference — US labelling, may differ from UK

DOSAGE AND ADMINISTRATION Important Dosage and Administration Instructions Acetaminophen and codeine phosphate tablets should be prescribed only by healthcare professionals who are knowledgeable about the use of opioids and how to mitigate the associated risks. Use the lowest effective dosage for the shortest duration of time consistent with individual patient treatment goals [see Warnings]. Because the risk of overdose increases as opioid doses increase, reserve titration to higher doses of Acetaminophen and codeine phosphate tablets for patients in whom lower doses are insufficiently effective and in whom the expected benefits of using a higher dose opioid clearly outweigh the substantial …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2025-12-23. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

Codeine is a prodrug converted by CYP2D6 to morphine, which acts on opioid receptors; analgesic effect therefore varies with metaboliser status.

Prescribing in practice

  • Effect varies with CYP2D6 status — ultra-rapid metabolisers risk toxicity and poor metabolisers gain little benefit.
  • MHRA restrictions: avoid in children under 12, after tonsillectomy/adenoidectomy for obstructive sleep apnoea in under-18s, and in breastfeeding.
  • It is a controlled drug — counsel on constipation, dependence and additive sedation/respiratory depression with other CNS depressants.

Monitoring

Review pain relief, bowel habit and signs of dependence; reassess the ongoing need.

Counselling the patient

  • It commonly causes constipation — a laxative may be needed.
  • Do not combine it with alcohol or other sedatives.
  • Take it only as prescribed; it can be habit-forming.

Evidence & guidelines

A step on the analgesic ladder for mild-to-moderate pain, with MHRA safety restrictions in children and breastfeeding.

Reference: MHRA Drug Safety Update; 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.

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