Drug interactions
Codeine + Morphine
Severity: Major
Codeine and Morphine: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Both are opioid agonists, and codeine is partly converted to morphine, so combining them duplicates therapy and increases the risk of sedation, respiratory depression and constipation. There is generally no rationale for using them together.
What this interaction means in plain words
Codeine and Morphine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Codeine belongs to Musculoskeletal; Morphine belongs to Musculoskeletal.
Why it happens
Additive opioid receptor agonism, with codeine being partly metabolized to morphine.
What to do
Avoid therapeutic duplication; use a single opioid at a time and adjust the dose by response. If rotation is needed, apply equianalgesic conversion with reduction for incomplete cross-tolerance.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Morphine
- Alvimopan + Morphine Contraindicated
- Isocarboxazid + Morphine Contraindicated
- Morphine + Olanzapine / samidorphan Contraindicated
- Morphine + Phenelzine Contraindicated
- Morphine + Tranylcypromine Contraindicated
- Alfentanil + Morphine Major
Other interactions of Codeine
- Alvimopan + Codeine Contraindicated
- Codeine + Isocarboxazid Contraindicated
- Codeine + Olanzapine / samidorphan Contraindicated
- Codeine + Phenelzine Contraindicated
- Codeine + Tranylcypromine Contraindicated
- Alfentanil + Codeine Major
Frequently asked questions
Can I take Codeine with Morphine?
MediHelp rates the interaction as major. Codeine and Morphine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Both are opioid agonists, and codeine is partly converted to morphine, so combining them duplicates therapy and increases the risk of sedation, respiratory depression and constipation. There is generally no rationale for using them together.
How serious is the interaction between Codeine and Morphine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid therapeutic duplication; use a single opioid at a time and adjust the dose by response. If rotation is needed, apply equianalgesic conversion with reduction for incomplete cross-tolerance.
What other medicines interact with Morphine?
MediHelp also lists interactions of Morphine with, for example, Alvimopan, Isocarboxazid, Olanzapine / samidorphan. The full list is on the Morphine page.
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