Tier C

L-Tryptophan

Also known as: Tryptophan · L-Trp · TRP

2 PMID anchor · CNS · METABOLISM · Last reviewed 2026-06-08

Read full dossier → JSON (tryptophan.json)

Mechanism of action

De novo NAD+ via kynurenine pathway (60 mg Trp -> 1 mg niacin equivalent)
Serotonin precursor
Melatonin precursor

Molecular + tissue targets

NAD+ pool (kynurenine route)
Serotonin synthesis
Melatonin synthesis
TDO/IDO enzymes

Dosage range

5 mg/kg/day RDA · 500-2000 mg/day mood/sleep (caution SSRI interaction · Tier C · Arnone 2018 PMID 29940237 kynurenine pathway mood SR+MA)

Safety notes

Drug interaction with SSRI/MAOI (serotonin syndrome risk) · pregnancy generally safe at RDA · 1989 EMS outbreak associated with contaminated supplement (not pure tryptophan)

Cross-market regulatory status

🇺🇸 FDA

GRAS (amino acid food ingredient · post-1995 reinstatement)

🇪🇺 EFSA

Reg 432/2012 rejected mood claims 2010 · no authorized health claim

🇧🇷 ANVISA

RDC 243/2018 dietary supplement framework · IN 28/2018 no Anexo V claim

Evidence anchors (PubMed) · 2

PMID 29940237 Meta-analysis review

Arnone D (2018) Neurosci Biobehav Rev

Role of Kynurenine Pathway and its Metabolites in Mood Disorders: A Systematic Review and Meta-Analysis of Clinical Studies

SR+MA kynurenine pathway dysregulation in mood disorders (not tryptophan supplementation directly · documents pathway alterations in depression) · verified 2026-06-07 · PMCID PMC6686193
PMID 32853625 Meta-analysis review

Hunt C (2020) Neurosci Biobehav Rev

Effect of immune activation on the kynurenine pathway and depression symptoms - A systematic review and meta-analysis

SR+MA immune activation kynurenine pathway depression symptoms (not direct tryptophan intervention) · verified 2026-06-07 · PMCID PMC8087452

Common use cases

mood support (educational · evidence mixed)
sleep support
NAD+ alternate precursor

Cross-reference

Health goals: cognitive support

Lifestyles: high stress

Full dossier: /ingredients/tryptophan/

Machine-readable JSON: /api/nc/tryptophan.json