L-Tryptophan

Tryptophan

Snapshot

Indications	Contraindications
Sleep quality¹ Waking after sleep onset¹ Mood in healthy adults² Anxiety in healthy adults² Mood in healthy adults^{2, 3}	Prescription antidepressant use⁴ Pregnancy or breastfeeding⁴

L-tryptophan is an essential amino acid and the dietary precursor of serotonin and melatonin; ingesting it raises brain serotonin synthesis. That effect drives its use for sleep disturbance, for mood and anxiety in healthy adults, and for depressed mood, where trials are few².

A meta-analysis found tryptophan shortened wake after sleep onset without changing other sleep components. Evidence for L-tryptophan alone in depression is sparse⁵. In a 2021 uncontrolled study of cancer patients with hot flushes, fatigue, and insomnia, supplementation was well tolerated and symptom scores improved; no controlled trial has tested it. Products list L-tryptophan mostly as capsules and powders; see Form comparison.

The most consequential caution is serotonergic, since tryptophan raises serotonin production⁶. Health Canada lists asking a practitioner before use in people taking antidepressants⁷ and in pregnancy⁷. The 1989 eosinophilia-myalgia outbreak was traced to contaminants in one manufacturer's product.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

68 sources, 49 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources