Morphine conversion and pharmacology
The prototypic opioid analgesic; the standard against which others are compared. Used for moderate to severe pain.
Equianalgesic estimate
10mg Parenteral ≈ 30mg Oral
Published equianalgesic ratios vary between references and with clinical context. Read how to interpret conversion results before applying an estimate.
Mechanism of action
Full agonist, primarily at the mu-opioid receptor (MOR) in the CNS and PNS. Also has affinity for delta (DOR) and kappa (KOR) receptors.
Brand names: MS Contin, Kadian, Roxanol, Duramorph
Pharmacokinetics
- Protein binding
- 20-35%
- Volume of distribution
- 1-6 L/kg
- Half-life
- 2-4 hours (IV/IR)
| Route | Form | Bioavailability | Onset | Peak | Duration |
|---|---|---|---|---|---|
| Oral | IR | 20-40% | 20-30 min | 60 min | 3-7 hours |
| Oral | ER | — | — | — | 12-24 hours |
| Parenteral | IV | 100% | 5-10 min | 20 min | 3-5 hours |
| Parenteral | IM/SC | — | 10-30 min | 30-60 min | 3-5 hours |
Metabolism
- Glucuronidation (primarily UGT2B7)
Metabolites
- Morphine-6-glucuronide (M6G) Active analgesic, more potent than morphine.
- Morphine-3-glucuronide (M3G) No analgesic activity; associated with neuroexcitatory effects (e.g., myoclonus, hyperalgesia).
Significant first-pass metabolism leads to low oral bioavailability. Metabolites are renally excreted. Interactions primarily with other CNS depressants.
Renal and hepatic impairment
Renal
Avoid or use extreme caution (especially GFR <30 mL/min). Accumulation of M6G (risk of respiratory depression) and M3G (risk of neurotoxicity) occurs.
Hepatic
Clearance is reduced; requires significant dose reduction and increased dosing interval.
Clinical cautions
- Hydrophilic compared to fentanyl.
- Histamine release may cause pruritus and hypotension.
For qualified healthcare professionals. This page is an educational reference, not prescribing advice. Check medicine information and conversion factors against a current clinical source and local guidance.
Other opioids in this reference
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Last updated 30 August 2026. Read how to interpret conversion results and the Terms of Service.