Morphine (Oral)

How it works

It is a full agonist at mu-opioid receptors in the central nervous system and periphery, reducing the perception of and emotional response to pain and depressing the brainstem respiratory centre.

Prescribing in practice

• Respiratory depression is the most serious risk and is potentiated by other CNS depressants such as benzodiazepines, gabapentinoids and alcohol, so co-prescribe with caution.
• Do not confuse or interchange immediate-release and modified-release preparations, and reduce doses in renal impairment and the elderly because the active metabolite accumulates.
• Anticipate and treat constipation, nausea and sedation, and counsel on the risks of tolerance and dependence with prolonged use.

Monitoring

Monitor pain control, sedation level, respiratory rate and bowel function, reviewing the dose regularly and tapering rather than stopping abruptly after prolonged use.

Counselling the patient

• This medicine can cause drowsiness, so do not drive or operate machinery until you know how it affects you.
• Take a regular laxative, as constipation is very common.
• Do not drink alcohol, and never take more than prescribed.

Evidence & guidelines

Oral morphine is recommended as a first-line strong opioid for cancer pain in NICE and WHO analgesic ladder guidance.