Tryptophan

Also known as l-tryptophan, tryptophane.

Last reviewed October 9, 2026 · Jump to references

What is Tryptophan?

In plain words

Tryptophan is a building block of protein found in foods, and the body cannot make it on its own. The body uses it to build proteins and make substances involved in mood, sleep, and energy processing. Researchers study tryptophan supplements for sleep and mood, but evidence of benefit is limited and mixed. Supplements can interact with medicines that raise serotonin, a chemical that helps nerve cells communicate.

Technical definition

L-tryptophan is an essential aromatic α-amino acid with an indole side chain that humans must obtain from dietary sources. It is incorporated into proteins and metabolized through pathways that produce serotonin, melatonin, and kynurenine metabolites, including precursors for NAD⁺ synthesis; it acts primarily as a metabolic substrate rather than a selective receptor agonist. It is sold as a dietary supplement in the United States, where supplements are not FDA-approved for safety or effectiveness before marketing.

Educational information only. This page does not provide medical advice or determine whether a supplement is appropriate for you. Review supplements with a qualified healthcare professional, especially if you take medication, are pregnant, have surgery scheduled, or have a chronic medical condition.

Important cautions

Serotonin syndrome riskhigh concern
Tryptophan increases serotonin production. Combined with SSRIs, SNRIs, MAOIs, triptans, tramadol, linezolid or St. John's wort it can cause serotonin syndrome, which needs emergency care.
Historical contaminationhigh concern
Contaminated tryptophan products were linked to an outbreak of eosinophilia-myalgia syndrome, a serious and sometimes fatal condition. Product quality and independent testing matter.
Drowsinessmoderate concern
Can cause daytime sleepiness and adds to sedatives and alcohol; avoid driving until effects are known.

Discuss with a clinician if any of these apply

Pregnancy or breastfeeding

Evidence by use

Each use is rated on its own. There is no single overall effectiveness score.