Drug interactions
Methylene blue + Morphine
Severity: Major
Methylene blue 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
Methylene blue is a potent MAO-A inhibitor and has been linked to serotonin syndrome with serotonergic drugs. Morphine has weak serotonergic activity so risk is lower than for agents such as meperidine or methadone, but regulators still warn about opioids.
What this interaction means in plain words
Methylene blue 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.
Why it happens
MAO-A inhibition by methylene blue increases serotonin, adding to weak serotonergic effects of morphine.
What to do
Avoid if possible; if methylene blue is essential, stop or minimize morphine and monitor for agitation, hyperthermia, clonus and autonomic instability. Consider a non-serotonergic analgesic alternative.
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
Frequently asked questions
Can I take Methylene blue with Morphine?
MediHelp rates the interaction as major. Methylene blue 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. Methylene blue is a potent MAO-A inhibitor and has been linked to serotonin syndrome with serotonergic drugs. Morphine has weak serotonergic activity so risk is lower than for agents such as meperidine or methadone, but regulators still warn about opioids.
How serious is the interaction between Methylene blue 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 if possible; if methylene blue is essential, stop or minimize morphine and monitor for agitation, hyperthermia, clonus and autonomic instability. Consider a non-serotonergic analgesic alternative.
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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