Drug interactions
Morphine + Pentazocine
Severity: Major
Morphine and Pentazocine: 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
Pentazocine is a mixed agonist-antagonist that can reduce morphine analgesia and precipitate withdrawal in opioid-dependent patients. It also adds to sedation and respiratory depression in others.
What this interaction means in plain words
Morphine and Pentazocine 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.
Morphine belongs to Musculoskeletal; Pentazocine belongs to Musculoskeletal.
Why it happens
Pentazocine acts as a kappa agonist and weak mu antagonist or partial agonist, competing with morphine at mu receptors.
What to do
Avoid combining in patients physically dependent on morphine; use a single full agonist for analgesia. If unavoidable, monitor for withdrawal symptoms, pain control and respiratory depression.
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 Pentazocine
- Calcium / magnesium / potassium / sodium oxybates + Pentazocine Contraindicated
- Olanzapine / samidorphan + Pentazocine Contraindicated
- Pentazocine + Phenelzine Contraindicated
- Pentazocine + Tranylcypromine Contraindicated
- Alfentanil + Pentazocine Major
- Alprazolam + Pentazocine Major
Frequently asked questions
Can I take Morphine with Pentazocine?
MediHelp rates the interaction as major. Morphine and Pentazocine 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. Pentazocine is a mixed agonist-antagonist that can reduce morphine analgesia and precipitate withdrawal in opioid-dependent patients. It also adds to sedation and respiratory depression in others.
How serious is the interaction between Morphine and Pentazocine?
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 combining in patients physically dependent on morphine; use a single full agonist for analgesia. If unavoidable, monitor for withdrawal symptoms, pain control and respiratory depression.
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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