L-Tryptophan

amino acidL-tryptophan

What is it

L-tryptophan is an essential amino acid the body cannot synthesize, obtained from dietary protein. It serves as the precursor to serotonin, melatonin, and niacin, and is a building block of many proteins.

How it works

Of the tryptophan you eat, the majority is used for protein synthesis. A smaller fraction enters two key metabolic pathways. The serotonin pathway converts tryptophan to 5-HTP and then to serotonin, primarily in the brain (small amounts) and gut (the majority of body serotonin). Serotonin in turn is converted to melatonin in the pineal gland at night. The kynurenine pathway, which handles most non-protein tryptophan, produces niacin (vitamin B3) and a variety of neuroactive metabolites including some involved in immune signaling. Brain tryptophan availability depends on competition with other large neutral amino acids for the same blood-brain barrier transporter. Eating carbohydrates raises insulin, which pulls other amino acids into peripheral tissues but spares tryptophan because it is bound to albumin. This is the mechanism behind the post-pasta sleepiness that some people associate with carb-heavy meals. Pure tryptophan supplements bypass the competition by raising tryptophan disproportionately.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Sleep onset and quality

Grade C

Moderate evidence

Older trials showed 1 to 2 grams of L-tryptophan before bed reduced sleep latency and improved subjective sleep quality. The evidence base is older but reasonably consistent for mild to moderate sleep complaints. Less effective for severe insomnia than prescription options.

Depression and mood disorders

Grade C

Moderate evidence

A 2002 Cochrane Review of 108 studies concluded tryptophan and 5-HTP were better than placebo at alleviating depression, but evidence quality was limited. Not a first-line treatment for moderate or severe depression but may be considered as adjunct under clinician supervision.

Premenstrual dysphoric disorder

Grade C

Moderate evidence

Trials of 6 grams per day during the late luteal phase have shown reductions in mood symptoms, irritability, and tension compared to placebo. Effective doses are high and side effect burden is significant.

Seasonal affective disorder

Grade D

Mixed evidence

Some small trials suggest tryptophan combined with light therapy may improve symptoms of seasonal affective disorder. Evidence is limited and serotonergic medication is the standard pharmacological treatment.

Smoking cessation

Grade D

Mixed evidence

Small trials have examined tryptophan as an adjunct to smoking cessation programs, with mixed results. Not part of standard cessation protocols.

2 commercial forms

L-tryptophan (pharmaceutical grade)

Well absorbed orally; brain delivery depends on coingestion of carbs vs other proteins.

Standard form, available as capsules or powder. Quality and purity vary; choose reputable manufacturers given the historical EMS contamination concern.

L-tryptophan with vitamin B6 and B3

B-vitamin cofactors support the conversion to serotonin and may reduce side effects.

Combinations are marketed to optimize the serotonin synthesis pathway. Independent evidence of clinical advantage over plain tryptophan is limited.

Dosage

The US RDA for adults is 4 mg per kilogram body weight per day, easily met by typical diets (an adult eating 70 grams of protein gets roughly 700 to 1,100 mg of tryptophan daily). Supplemental doses for sleep are 500 mg to 2 grams before bed; for mood, 1 to 3 grams per day in divided doses; for premenstrual dysphoric disorder, around 6 grams per day in research. Start low to assess tolerance.

When and how to take it

For sleep, take 500 mg to 2 grams of L-tryptophan 30 to 60 minutes before bed on an empty stomach, or 1 to 2 hours after a small carbohydrate snack to take advantage of insulin-driven competition that helps tryptophan cross into the brain. For mood support, split doses across the day with meals. Avoid high-protein meals at the same time as the dose, because other large neutral amino acids compete with tryptophan for the same blood-brain barrier transporter. Pair with a small carb like a banana or crackers to maximize central availability.

Food sources

Food	Amount	%DV
Turkey (3 oz)	~250 to 350 mg	—
Chicken (3 oz)	~290 mg	—
Salmon (3 oz)	~250 mg	—
Eggs (1 large)	~75 mg	—
Cheddar cheese (1 oz)	~90 mg	—
Pumpkin seeds (1 oz)	~160 mg	—
Soybeans (1 cup cooked)	~600 mg	—
Oats (1 cup cooked)	~150 mg	—

Safety

L-tryptophan is generally well tolerated at typical doses, with mild drowsiness, nausea, headache, dry mouth, or dizziness as the most common side effects. The historical concern is eosinophilia-myalgia syndrome (EMS), a serious connective tissue disorder that caused dozens of deaths in 1989 and was traced to contaminated batches from a single Japanese manufacturer. L-tryptophan was pulled from the US market and only returned in 2001 after manufacturing standards were tightened. Modern pharmaceutical-grade tryptophan has not been linked to new EMS outbreaks, but the historical episode shapes ongoing regulatory caution. Serotonin syndrome is the major acute risk, particularly when combined with serotonergic medications. No formal Tolerable Upper Intake Level has been established. Doses above 3 to 4 grams per day in a single sitting can cause notable sedation and GI upset.

Who should be cautious

Avoid combining with serotonergic prescription medications without psychiatric oversight. Pregnant and breastfeeding women should rely on dietary tryptophan rather than supplements. People with liver disease, eosinophilia, scleroderma, or autoimmune connective tissue disorders should consult a clinician given the historical EMS link. Children and adolescents should generally avoid supplementation without specialist guidance.

Interactions

L-tryptophan can cause serotonin syndrome when combined with SSRIs, SNRIs, MAOIs, tricyclic antidepressants, tramadol, triptans, lithium, and St. John's wort. Sedating effects may add to alcohol, benzodiazepines, and other CNS depressants. Combination with carbidopa (used in Parkinson's) requires caution. May potentiate effects of antiparkinsonian medications.

Frequently asked questions

Does turkey really make you sleepy?⌄

Turkey has roughly the same tryptophan content as chicken or beef. The Thanksgiving sleepiness story is more about post-meal carbohydrate-driven insulin spikes (which favor tryptophan crossing into the brain) and the volume of food consumed than turkey itself.

Is tryptophan still legal in the US?⌄

Yes. After the 1989 EMS outbreak traced to a contaminated supply, tryptophan was effectively pulled and returned to the US market in 2001 with stricter manufacturing standards. Pharmaceutical-grade tryptophan has not been linked to new EMS cases.

Should I take tryptophan or 5-HTP?⌄

5-HTP bypasses the rate-limiting enzyme that converts tryptophan to 5-HTP, so it's more potent per milligram and reaches serotonin more directly. Tryptophan has more uses (protein synthesis, niacin) and a milder GI profile for many people. For sleep or mood, either can work.

Can I take tryptophan with my antidepressant?⌄

Not without psychiatric supervision. Combining tryptophan with SSRIs, SNRIs, MAOIs, or other serotonergic medications can cause serotonin syndrome, a potentially dangerous overload of serotonergic activity.

Why take tryptophan with carbs?⌄

A small carbohydrate snack raises insulin, which pulls other amino acids (the ones competing with tryptophan for the blood-brain barrier transporter) into peripheral tissue. That leaves tryptophan with less competition for brain uptake, increasing central serotonin synthesis.

References

Wikidata: L-Tryptophan — Wikidata link

Track L-Tryptophan with Pilora

Set up dose reminders, check interactions, and join the community in the Pilora iPhone app.

Coming to App Store

Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.