Drug interactions
Isoniazid + L-tryptophan
Severity: Moderate
Isoniazid and L-tryptophan: moderate interaction.
Last updated
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
Isoniazid has weak monoamine oxidase inhibiting activity, and L-tryptophan is a serotonin precursor. Together they could raise serotonergic activity and, in rare cases, contribute to serotonin syndrome. Clinical reports are sparse.
What this interaction means in plain words
Isoniazid and L-tryptophan can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Additive serotonergic effect from weak MAO inhibition by isoniazid and increased serotonin synthesis from tryptophan.
What to do
Avoid unnecessary tryptophan supplementation during isoniazid therapy. If both are used, monitor for agitation, tremor, hyperreflexia, sweating and hyperthermia, and stop tryptophan if symptoms appear.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Isoniazid
Frequently asked questions
Can I take Isoniazid with L-tryptophan?
MediHelp rates the interaction as moderate. Isoniazid and L-tryptophan can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Isoniazid has weak monoamine oxidase inhibiting activity, and L-tryptophan is a serotonin precursor. Together they could raise serotonergic activity and, in rare cases, contribute to serotonin syndrome. Clinical reports are sparse.
How serious is the interaction between Isoniazid and L-tryptophan?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid unnecessary tryptophan supplementation during isoniazid therapy. If both are used, monitor for agitation, tremor, hyperreflexia, sweating and hyperthermia, and stop tryptophan if symptoms appear.
What other medicines interact with Isoniazid?
MediHelp also lists interactions of Isoniazid with, for example, Bacillus calmette-guerin substrain tice, Benzhydrocodone / acetaminophen, Carbamazepine. The full list is on the Isoniazid page.
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