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Strong Opioid Analgesic — Step 3 WHO Ladder Pregnancy: Use only if benefit outweighs risk — neonatal opioid withdrawal syndrome; respiratory depression in neonate if used near delivery. Opioids used in labour (pethidine, remifentanil) under obstetric guidance.

Morphine (Oral)

Brand names: Oramorph (oral solution), Sevredol (immediate-release tablet), MST Continus (modified-release), MXL (modified-release)

Adult dose

Dose: Immediate-release (Oramorph/Sevredol): 5–10mg every 4 hours (titrate to pain; usual range 5–30mg every 4h). Modified-release (MST Continus): total 24h IR dose divided into BD dosing — e.g. 30mg/day IR = MST 15mg BD. Breakthrough dose: 1/6 of total daily MR dose as IR morphine every 1–2h as needed.
Route: Oral
Frequency: Every 4 hours (IR); twice daily (MR)
Max: No ceiling dose in cancer pain — titrate to effect. In non-cancer pain: lowest effective dose; review regularly.
First-line strong opioid for moderate-to-severe pain. Titrate IR morphine to establish 24h requirement, then convert to MR formulation. MR formulations must not be crushed. Opioid rotation may be needed if intolerable side effects. Schedule 2 Controlled Drug.

Paediatric dose

Dose: 0.2 mg/kg
Route: Oral
Frequency: Every 4 hours
Max: 0.2mg/kg per dose (max 10mg per dose in most children)
BNFc: 1–12 months: 80–200 micrograms/kg every 4h. 1–5 years: 2.5–5mg every 4h. 6–11 years: 5–10mg every 4h. 12–17 years: 5–20mg every 4h. Modified-release available for children ≥1 year. Seek specialist paediatric pain team opinion.

Dose adjustments

Renal

eGFR 10–50: reduce dose by 25%, increase dosing interval to every 6h. eGFR <10: avoid or use with extreme caution — active metabolite morphine-6-glucuronide (M6G) accumulates; causes profound sedation and respiratory depression.

Hepatic

Severe hepatic impairment: reduce dose and frequency; accumulation risk. Use with caution — monitor closely.

Paediatric weight-based calculator

BNFc: 1–12 months: 80–200 micrograms/kg every 4h. 1–5 years: 2.5–5mg every 4h. 6–11 years: 5–10mg every 4h. 12–17 years: 5–20mg every 4h. Modified-release available for children ≥1 year. Seek specialist paediatric pain team opinion.

Clinical pearls

  • Always prescribe a laxative (macrogol or senna + docusate) with regular morphine — opioid-induced constipation is universal and does not develop tolerance; antiemetics (metoclopramide, cyclizine) for first 1–2 weeks at initiation
  • Antidote for opioid toxicity: naloxone 400 micrograms IV/IM — titrate in 100-microgram increments to avoid precipitating acute withdrawal; repeat every 2–3 minutes; infusion may be needed (naloxone half-life shorter than morphine)
  • M6G accumulation in renal failure: morphine is dangerous in CKD — consider oxycodone (shorter active metabolite accumulation), hydromorphone, or alfentanil as alternatives
  • Breakthrough pain rule: 1/6 of total daily MR dose given as IR for breakthrough — review rescue medication use over 24h to guide MR dose increase

Contraindications

  • Acute respiratory depression
  • Comatose patients
  • Head injury with raised ICP (relative)
  • Acute abdomen (relative)
  • Paralytic ileus
  • MAOIs within 14 days
  • Hypersensitivity to morphine

Side effects

  • Constipation (universal — always prescribe laxative prophylactically)
  • Nausea and vomiting (common at initiation — usually resolves)
  • Sedation
  • Respiratory depression (dose-dependent)
  • Pruritus
  • Urinary retention
  • Miosis
  • Confusion / delirium (particularly elderly)
  • Tolerance and dependence
  • Hyperalgesia (paradoxical — at high doses)

Interactions

  • MAOIs — avoid (serotonin syndrome, CNS excitation)
  • CNS depressants, benzodiazepines, alcohol — additive respiratory depression (MHRA warning)
  • Gabapentinoids (pregabalin, gabapentin) — additive respiratory depression — monitor closely

Monitoring

  • Pain score (NRS 0–10)
  • Sedation score
  • Respiratory rate (>8/min)
  • Bowel function (constipation)
  • Breakthrough analgesia use (guide dose titration)
  • Opioid dependence risk (non-cancer pain)

Reference: BNFc; BNF 90; NICE NG31 (Cancer Pain); WHO Analgesic Ladder; Palliative Care Formulary (PCF6). Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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