What kind of interaction is it?

Caution: an interaction that may reduce efficacy or raise side-effect risk and warrants monitoring.

Is this interaction backed by published research?

Yes. NutriStack lists 1 citation row for the Isoniazid + L-Tryptophan pair, each linking to PubMed by PMID where available. Full sourcing methodology at https://nutristackapp.com/methodology/interactions.

Supplement × Prescription·a caution·Emerging evidence

Isoniazid + L-Tryptophan

Q: Can I take Isoniazid and L-Tryptophan together?

Possibly, but with caution. Isoniazid and L-Tryptophan have a documented caution-tier interaction. Isoniazid is a weak, reversible inhibitor of monoamine oxidase. Combining it with high doses of L-tryptophan, a precursor to serotonin, can increase serotonergic activity and theoretically contribute to serotonin excess, particularly when other serotonergic agents are also present.

Q: How does this affect a NutriStack Stack Score?

-5 to your Stack Score per scored caution row.

Caution Emerging evidence

Isoniazid is a weak, reversible inhibitor of monoamine oxidase. Combining it with high doses of L-tryptophan, a precursor to serotonin, can increase serotonergic activity and theoretically contribute to serotonin excess, particularly when other serotonergic agents are also present.

Supplement × Prescription

Open the interaction checker → Read the methodology

From the database

What the row says.

Every entry follows the same shape: what is happening, the mechanism, and the recommendation.

Substances

Isoniazid and L-Tryptophan

Pair type

Caution

Evidence

Emerging

Source citations

Scope

Supplement × Prescription

Last verified

June 4, 2026

CautionEmerging evidence

What is happening. Isoniazid is a weak, reversible inhibitor of monoamine oxidase. Combining it with high doses of L-tryptophan, a precursor to serotonin, can increase serotonergic activity and theoretically contribute to serotonin excess, particularly when other serotonergic agents are also present.

Mechanism. Isoniazid inhibits monoamine oxidase, reducing breakdown of monoamine neurotransmitters. Increased serotonin precursor load from L-tryptophan combined with reduced monoamine metabolism can raise central serotonin levels.

Recommendation. Use caution when combining L-tryptophan with isoniazid, particularly at higher tryptophan doses or alongside other serotonergic medications. Watch for agitation, tremor, sweating, rapid heartbeat, or confusion and seek care if these occur. Discuss use with a clinician before starting.

Stack Score

How it moves the number.

Effect on the composite score

If both Isoniazid and L-Tryptophan are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).

The full algorithm, the clamping rules, and four worked stacks are at /methodology/stack-score.

Sources

Sources, by evidence tier.

Every claim on this page is cited. PMIDs link straight to PubMed.

Reference material

1Boyer EW, Shannon M. The serotonin syndrome. New England Journal of Medicine. 2005.Needs sourceNo link

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