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L-Tryptophan

precursor to serotonin and melatonin

amino-acid
Human trial evidenceTraditional useInteraction riskNeeds more research

Essential amino acid precursor to serotonin and melatonin.

L-Tryptophan is an essential amino acid, meaning it cannot be produced by the body and must be obtained through diet. It serves as a precursor for several important molecules, including serotonin, a neurotransmitter involved in mood regulation, sleep, and appetite. It is also a precursor for melatonin, a hormone that regulates sleep-wake cycles, and niacin (vitamin B3). Due to its role in serotonin and melatonin synthesis, L-Tryptophan has been explored for its potential effects on sleep, mood, and other neurological functions. It is naturally found in many protein-rich foods.

Quick answer

What it is: L-Tryptophan is an essential amino acid, meaning it cannot be produced by the body and must be obtained through diet.

May support:Seasonal Affective Disorder, Fibromyalgia

Evidence Summary

The current understanding of L-Tryptophan's biological roles is based on established biochemical pathways and observational studies. However, specific clinical efficacy for various conditions requires more robust, controlled human trials.

Last reviewed · Jun 2026

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Commonly Combined With

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Why It Works

Crosses BBB; converted to 5-HTP then serotonin.

How it works in more detail

Upon absorption, L-Tryptophan crosses the blood-brain barrier and is hydroxylated by tryptophan hydroxylase to form 5-hydroxytryptophan (5-HTP). This is the rate-limiting step in serotonin synthesis. 5-HTP is then decarboxylated by L-amino acid decarboxylase to produce serotonin (5-hydroxytryptamine, 5-HT). Serotonin acts as a neurotransmitter in the central nervous system, influencing mood, sleep, appetite, and cognition. In the pineal gland, serotonin is acetylated and then methylated to form melatonin, a hormone critical for regulating circadian rhythms and sleep.

How to use

Always consult a qualified clinician.

Editorial guidance

Suggested dosage
500–2000 mg before bed
Research dosage range
Research studies have used a wide range of L-Tryptophan dosages, often between 1 gram and 6 grams per day, depending on the condition being investigated.
Typical onset
Effects related to sleep or mood may be noticed within 30 minutes to a few hours after ingestion, though consistent benefits may require several days or weeks of regular use.
Typical forms
capsule, powder
Quality markers
When purchasing L-Tryptophan, look for products from reputable manufacturers that provide third-party testing for purity and absence of contaminants. Ensure the product is free from unnecessary fillers and artificial ingredients.
Medication interactions
  • SSRIs (Selective Serotonin Reuptake Inhibitors)
  • MAOIs (Monoamine Oxidase Inhibitors)
  • Tricyclic antidepressants
  • Sedatives
  • Triptans
  • Dextromethorphan (cough medicine)
Avoid if
  • Pregnant or breastfeeding (lack of sufficient safety data)
  • History of Eosinophilia-Myalgia Syndrome (EMS)
  • Liver disease
  • Kidney disease

Community tips

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Suggested dosage

500–2000 mg before bed

General guidance — discuss specifics with a clinician.

Active medicinal compounds

L-Tryptophan is the primary active compound.

Traditional use

As an isolated amino acid, L-Tryptophan does not have a history of traditional use in herbal medicine systems. However, foods rich in L-Tryptophan have been consumed for centuries and are an integral part of human diets.

Safety

Safety warnings

Serotonin syndrome risk with SSRIs.

Avoid if

  • Pregnant or breastfeeding (lack of sufficient safety data)
  • History of Eosinophilia-Myalgia Syndrome (EMS)
  • Liver disease
  • Kidney disease

Medication interactions

  • SSRIs (Selective Serotonin Reuptake Inhibitors)
  • MAOIs (Monoamine Oxidase Inhibitors)
  • Tricyclic antidepressants
  • Sedatives
  • Triptans
  • Dextromethorphan (cough medicine)

Reported side effects

  • Nausea
  • Dizziness
  • Drowsiness
  • Headache
  • Dry mouth
  • Stomach upset

General guidance — discuss specifics with a clinician.

Evidence ecosystem

Scientific literature, clinical guidance, government sources, ongoing research, traditional use, and lived experience — grouped by source type and quality.

Overall grade

The current understanding of L-Tryptophan's biological roles is based on established biochemical pathways and observational studies. However, specific clinical efficacy for various conditions requires more robust, controlled human trials.

Filter by source type

Randomized Human Trials(1)

Controlled human studies with random assignment.

High Quality

  • Regression of gastroesophageal reflux disease symptoms using dietary supplementation with melatonin, vitamins and aminoacids: comparison with omeprazole.

    Pereira Rde S · Journal of pineal research · 2006 · n=176

    The prevalence of gastroesophageal reflux disease (GERD) is increasing. GERD is a chronic disease and its treatment is problematic. It may present with various symptoms including heartburn, regurgitation, dysphagia, coughing, hoarseness or chest pain. The aim of this study was to investigate if a dietary supplementation containing: melatonin, l-tryptophan, vitamin B6, folic acid, vitamin B12, methionine and betaine would help patients with GERD, and to compare the preparation with 20 mg omeprazole. Melatonin has known inhibitory activities on gastric acid secretion and nitric oxide biosynthesis. Nitric oxide has an important role in the transient lower esophageal sphincter relaxation (TLESR), which is a major mechanism of reflux in patients with GERD. Others biocompounds of the formula display anti-inflammatory and analgesic effects. A single blind randomized study was performed in which 176 patients underwent treatment using the supplement cited above (group A) and 175 received treatm

    Randomized TrialPubMedHigh Quality

Clinical Trial Registries(1)

Registered ongoing or completed trials (ClinicalTrials.gov).

Moderate Quality

Limitations: There is a lack of recent, high-quality, randomized controlled trials specifically on L-Tryptophan supplementation for many of its proposed uses. Much of the existing research may be older, have small sample sizes, or lack rigorous methodology. The direct clinical benefits and optimal dosages are not yet definitively established through comprehensive evidence.

This page is educational. Statements use phrases like "may support" and "has been studied for"because no remedy here is approved to cure, treat, or reverse any condition. Discussion happens on the ailment pages — community statistics here are derived from those reports. Always consult a qualified clinician.

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