Opioids · Pain & inflammation
Morphine
Statex® · MS Contin® · MSIR®(brand names vary by market)
The reference opioid, and the one the kidney cannot forgive.
Also: modified release, oral liquid, injection, infusion
Mechanism
Mu opioid receptor agonist in the dorsal horn, brainstem and limbic system: reduced ascending pain transmission, reduced affective response to pain, and reduced respiratory drive.
Indications
- Moderate to severe acute pain
- Cancer pain
- Breathlessness in palliative care
- Acute pulmonary oedema, historically
Formulations
Dosing concepts
Renal impairment
Morphine-6-glucuronide is active and renally cleared. In kidney failure it accumulates and produces sedation, myoclonus and respiratory depression days after a stable dose.
Breakthrough dosing
A breakthrough dose is a fraction of the total daily dose, so it scales with the background rather than being a fixed number.
Route conversion
Oral to parenteral conversions are not one to one, and getting the ratio wrong in either direction causes harm.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- ~30% oral, with high first-pass metabolism
- Half-life
- 2 to 4 h; active metabolites much longer in renal impairment
- Elimination
- hepatic: Glucuronidation to M3G and the active M6G, both renally cleared
- Protein binding
- ~35%
Adverse effects
- ConstipationcommonUniversal and permanent; no tolerance develops.
- Nausea and vomitingcommonUsually settles within days, unlike the constipation.
- Sedationcommon & seriousThe early warning sign of respiratory depression.
- Respiratory depressionserious
- Myoclonus and delirium in renal impairmentserious
- PrurituscommonHistamine-mediated and not an allergy.
- Tolerance, dependence and use disorderserious
Contraindications & precautions
Contraindications
- Respiratory depression
- Paralytic ileus
- Acute severe asthma without airway support
Precautions
- Renal impairment
- Older adults
- Concurrent benzodiazepines or other sedatives
- Head injury
- Obstructive sleep apnoea
Interactions
No curated interaction entries yet for this agent.
Monitoring
Sedation score
It precedes respiratory depression and is the earliest actionable sign · With every dose in the acute setting
Respiratory rate
Later than sedation, but decisive
Bowel function
From the first dose, not from the first complaint
Pain score AND function
Pain alone is a poor guide to whether opioid therapy is helping
Counselling points
- You will also need a laxative, from the start and for as long as you take this.
- Nausea usually settles after a few days.
- Do not drink alcohol or take sleeping tablets with it.
- Do not drive while the dose is changing.
- Keep it locked away; store and dispose of it safely.
Clinical pearls
- In a patient with poor kidney function, the drug can look fine for two days and then produce profound sedation as M6G accumulates. Hydromorphone is the usual substitute.
- Sedation always comes before respiratory depression. A drowsy patient on opioids needs attention now, not at the next observation round.
- Itch and flushing after morphine are usually histamine release, not allergy, and they do not preclude opioid therapy.
References & review
- Morphine product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.