Tryptophan

amino acid

What is it

Tryptophan is an essential amino acid the body cannot make and must obtain from food. It is the precursor to serotonin, melatonin, and niacin (vitamin B3), and a building block of body proteins. The naturally occurring biological form is L-tryptophan; supplements use this form.

How it works

Most dietary tryptophan goes into protein synthesis. The smaller fraction that doesn't enters two metabolic pathways. The serotonin pathway converts tryptophan to 5-HTP and then serotonin. The kynurenine pathway, which handles most non-protein tryptophan, produces niacin and immune-modulating metabolites. Brain tryptophan availability is gated by a transporter at the blood-brain barrier that also moves other large neutral amino acids (leucine, valine, isoleucine, phenylalanine, tyrosine). They compete with each other, which is why a high-protein meal can actually lower brain tryptophan even though it raises blood tryptophan: it raises everything else more. Carbohydrate-rich meals trigger insulin, which clears the competitor amino acids into muscle but leaves tryptophan free, raising its proportional share. This is one mechanism behind post-carb-meal sleepiness.

Evidence for 5 uses

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

Sleep onset latency

Grade C

Moderate evidence

Multiple older trials and a more recent 2022 meta-analysis suggest 1 gram or more of tryptophan before bed reduces sleep onset latency in adults with mild sleep complaints. Effects are modest and less pronounced than prescription sleep aids.

Depression

Grade C

Moderate evidence

A 2002 Cochrane Review of tryptophan and 5-HTP for depression concluded both were better than placebo, but evidence quality was limited and study designs varied. Not standard first-line treatment.

Premenstrual symptoms

Grade C

Moderate evidence

Tryptophan at 6 g/day during the late luteal phase has reduced PMS-related mood symptoms in some trials. Side effect burden at this dose is significant.

Pain perception

Grade D

Mixed evidence

Some studies suggest tryptophan supplementation modestly raises pain thresholds in chronic pain conditions, possibly through serotonergic modulation. Evidence base is small.

Aggression and irritability

Grade D

Mixed evidence

Acute tryptophan depletion experiments suggest serotonin modulates aggression, and some small trials have explored supplementation for reducing irritability and impulsive aggression. Effects are inconsistent.

2 commercial forms

L-tryptophan (free form)

Well absorbed orally; brain uptake influenced by competing large neutral amino acids.

Standard supplemental form. Capsules and powders both common. Buy from manufacturers with strong quality control.

Tryptophan + B6/B3 cofactor blends

B-vitamins support enzymatic conversion to serotonin and niacin.

Marketed as optimizing the serotonin pathway. Independent comparative evidence is limited but the cofactor logic is sound.

Dosage

The US RDA for adults is 4 mg per kilogram body weight per day, generally met by typical diets. Supplemental doses are 500 mg to 2 grams before bed for sleep, 1 to 3 grams per day in divided doses for mood support, and higher doses (up to 6 grams) in research protocols for PMDD. Start at lower doses and titrate.

When and how to take it

For sleep, take 500 mg to 2 grams 30 to 60 minutes before bed, preferably on an empty stomach or with a small carbohydrate snack. The carb-plus-tryptophan combination takes advantage of insulin-driven removal of competing amino acids, increasing tryptophan's share of the blood-brain barrier transporter. For mood, split daily doses across two or three administrations with light snacks rather than full protein-rich meals. Avoid taking with a large protein meal because the leucine, valine, isoleucine, and tyrosine in protein compete with tryptophan for brain uptake.

Food sources

Food	Amount	%DV
Turkey breast (3 oz)	~280 mg	—
Chicken breast (3 oz)	~290 mg	—
Salmon (3 oz)	~245 mg	—
Eggs (1 large)	~75 mg	—
Pumpkin seeds (1 oz)	~160 mg	—
Soybeans (1 cup cooked)	~600 mg	—
Milk (1 cup)	~115 mg	—
Tofu (1/2 cup)	~135 mg	—

Safety

Tryptophan is well tolerated at typical doses. Side effects include drowsiness, dry mouth, nausea, headache, and dizziness. The most notable historical safety concern is eosinophilia-myalgia syndrome (EMS), traced to a 1989 outbreak from contaminated batches by a single manufacturer; pharmaceutical-grade tryptophan re-entered the US market in 2001 with stricter manufacturing standards and has not been clearly associated with new EMS cases. Serotonin syndrome is the major acute risk when tryptophan is combined with serotonergic medications. No formal Tolerable Upper Intake Level has been established for supplemental tryptophan.

Who should be cautious

Avoid combining with serotonergic prescription medications without psychiatric guidance. Pregnant and breastfeeding women should rely on dietary intake. People with liver disease, autoimmune connective tissue conditions, or a history of eosinophilia should consult a clinician. Not generally recommended for children and adolescents without specialist input.

Interactions

Serotonin syndrome can occur when tryptophan is combined with SSRIs, SNRIs, MAOIs, tricyclic antidepressants, tramadol, triptans, lithium, or St. John's wort. Sedating effects may add to alcohol and benzodiazepines. Carbidopa and other dopaminergic medications can interact. Tryptophan may potentiate the sedative effect of antihistamines.

Frequently asked questions

Is L-tryptophan different from tryptophan?⌄

L-tryptophan is the naturally occurring biological form of tryptophan, and it is what supplements contain. D-tryptophan is the mirror-image isomer and is not biologically active in humans. When labels say 'tryptophan' they almost always mean L-tryptophan.

How much tryptophan should I take for sleep?⌄

Common doses are 500 mg to 2 g, taken 30 to 60 minutes before bed. Start at 500 mg and adjust. Pair with a small carbohydrate snack to favor brain uptake.

Can I combine tryptophan with melatonin?⌄

Yes, no known harmful interaction. Tryptophan is the upstream precursor to melatonin, so combining them is biochemically redundant but not unsafe. Many find one or the other sufficient.

Why is tryptophan more available after carbs?⌄

Carbs trigger insulin release, which clears the other large neutral amino acids (leucine, valine, isoleucine, tyrosine, phenylalanine) out of blood into muscle. Tryptophan is bound to albumin and is spared, so its share of the blood-brain barrier transporter rises after a carb-heavy meal.

Will tryptophan show up on a drug test?⌄

No. Tryptophan is a standard amino acid and does not produce metabolites detected on typical employment or sports drug screens.

References

Wikidata: Tryptophan — Wikidata link

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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.