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L-Tryptophan

Amino Acid ·Moderate evidence ·Reviewed May 2026

Essential amino acid precursor to serotonin and melatonin.

Evidence tier
Moderate
Indexed sources
17 1987–2025
Interactions
24
Cost / month
$5.40 budget
Read the sources → Compare profiles
What it's good for
  • Sleep support3,5
  • Mood enhancement13,14
  • Serotonin production14,15
What to watch for
  • Drowsiness
  • Nausea
  • Dry mouth
  • SSRIs/MAOIs (serotonin syndrome)15,2
  • Eosinophilia history15

The bottom line

Evidence rating moderate. Most-documented uses: sleep support, mood enhancement, serotonin production. 17 sources indexed (1987–2025), with 24 interaction records on file.

The science

How it works, mechanistically.

Core mechanism

Converted to 5-HTP by tryptophan hydroxylase, then to serotonin by AADC. Serotonin is further converted to melatonin by AANAT and ASMT in the pineal gland.14,15

Class
Essential Amino Acid
Found in food
Turkey, Chicken, Eggs
Low-status signs
Depression, Insomnia
Absorption
Best on an empty stomach
Dosing

Dosing & protocol.

Common range
500-1,000 mg before bed
Recommended form
Free-form L-Tryptophan

Take on empty stomach away from protein (competition for transport)3,5

Dosing protocol

Maintain · 500-2000 mg before bed on empty stomach

Empty stomach away from competing amino acids. Do not combine with SSRIs.15,16

No cycling requiredNo tolerance buildup
Forms

Forms & what to buy.

Ranked by evidence and value.

Free-Form L-Tryptophan Recommended
Rank 1: standard serotonin and melatonin precursor form. Limited direct form-comparison evidence; ranking is based on review or mechanistic data (PMID: 4074600). Take away from protein when possible.
Mid500-1000 mg at bedtime
Sustained-Release Tryptophan
Rank 2: slower-release form. Human comparative evidence is limited.
Premium500-1000 mg at bedtime
Tryptophan-Rich Protein
Rank 3: food-based source. Competes with other amino acids for transport.
BudgetFood based
Cost

What it actually costs.

Real-world pricing across three quality tiers. Assumes Free-Form L-Tryptophan.

BudgetBest value
$5.40 /mo
$0.18 per dose
Mid
$10.50 /mo
$0.35 per dose
Premium
$21.00 /mo
$0.70 per dose

Assumes 500-1,000 mg before bed. Vendor basis: NOW/iHerb, Vitacost, Life Extension, and Amazon marketplace; higher-dose capsules raise daily cost. Updated 2026-05-28.

From food

The same dose, as food.

How much you'd eat to match a supplemental dose.

500-1,000 mg L-tryptophan
About 5-8 ounces turkey or chicken, 4-6 ounces cheese, 4-6 eggs, 1-2 ounces pumpkin seeds, or soy foods can provide this range.

Foods provide tryptophan within protein and may not have the same timing effects as isolated bedtime dosing.

Goals

Goal-based dosing.

Sleep

Dose: 500-1,000 mg nightly3,5

Timing: 30-60 minutes before bed

Clinical dose evidence: PMID 33942088.

Lab work

Markers to track.

What to test, the optimal window inside the conventional range, and how long a response takes.

Plasma Tryptophan Tryptophan

L-tryptophan (500 to 2000 mg) raises plasma tryptophan and increases brain serotonin synthesis when taken away from competing amino acids.14,15

Optimal
50–80 micromol/L
Conventional
40–90 micromol/L
Responds in
Peak plasma at 1 to 2 hours; cleared within 12 hours.

Kynurenine to tryptophan ratio reflects inflammatory shunting of tryptophan away from serotonin. Track in chronic inflammation and depression workups.

Kynurenine/Tryptophan Ratio5-HIAA
Safety

Full safety detail.

Side effects

  • Drowsiness
  • Nausea
  • Dry mouth

Contraindications

  • SSRIs/MAOIs (serotonin syndrome)15,2
  • Eosinophilia history15
Interactions

Interaction records.

DangerousContraindicated

5-HTP

Both 5-HTP and L-Tryptophan increase serotonin synthesis. Combining them creates additive serotonin excess, risking serotonin syndrome.

Recommendation: Do NOT combine. Choose one serotonin precursor, not both.

DangerousContraindicated

St. John's Wort

St. John's Wort inhibits serotonin reuptake while L-Tryptophan increases serotonin synthesis. Risk of serotonin syndrome.

Recommendation: Do NOT combine without medical supervision.

DangerousContraindicated

SSRIs/SNRIs/MAOIs

L-Tryptophan is a serotonin precursor and can combine dangerously with serotonergic antidepressants or MAO inhibitors, increasing serotonin syndrome risk.

Recommendation: Do NOT combine L-tryptophan with SSRIs, SNRIs, MAOIs, or other serotonergic medications unless specifically directed by the prescriber managing the medication.

InfoConflict

L-Tyrosine

Tyrosine and tryptophan compete with each other (and with other large neutral amino acids) for transport across the blood-brain barrier; co-administration blunts the brain entry of each.

Recommendation: Separate by 2 to 3 hours. Tyrosine in morning for catecholamine support; tryptophan or 5-HTP at night for serotonin and sleep.

DangerousContraindicated

MDMA

L-Tryptophan combined with MDMA raises the risk of serotonin syndrome by supplying additional serotonin precursor on top of MDMA's serotonin-releasing effect.

Recommendation: Do not combine. Watch for high fever, agitation, tremor, or muscle rigidity and seek emergency medical care if they appear.

ModerateTiming Sensitive

BCAAs

This is the classic large neutral amino acid transporter competition described in the central fatigue hypothesis. BCAAs are sometimes used deliberately to lower brain serotonin during exercise, which is the opposite of why people supplement L-tryptophan (to raise serotonin for sleep or mood). Taking a large BCAA dose at the same time as L-tryptophan reduces tryptophan's passage into the central nervous system and can therefore reduce its intended benefit. The interaction is dose- and timing-dependent rather than a safety hazard.

Recommendation: Separate the two by at least 2 to 3 hours. Take L-tryptophan on its own, ideally on a relatively empty stomach or with a small carbohydrate source, away from any BCAA or high-protein dose. If L-tryptophan is for sleep, take it in the evening and keep BCAAs to around training earlier in the day. Avoid combining a large BCAA bolus (for example 5 to 10 g) with L-tryptophan in the same serving.

InfoSynergy

Vitamin B3

Tryptophan and niacin are linked through a single biosynthetic pathway. Supplemental tryptophan contributes to niacin/NAD+ status, and conversely, ensuring sufficient niacin reduces the diversion of tryptophan into niacin synthesis, leaving more tryptophan for serotonin production. This shared-pathway relationship is a well-established principle in nutrition science and is the basis for expressing niacin needs as niacin equivalents that include tryptophan.

Recommendation: No avoidance is needed; the relationship is generally complementary. If using L-Tryptophan (commonly 500 mg to 2000 mg, often at night for mood or sleep support), maintaining adequate niacin intake helps preserve tryptophan for serotonin synthesis. Cofactors for the conversion (vitamin B6, vitamin B2) should also be sufficient. They can be taken together; tryptophan is often dosed away from high-protein meals to aid uptake, which is a separate practical consideration.

SeriousCaution

Sertraline

L-Tryptophan is the dietary amino acid precursor to serotonin. Supplemental tryptophan increases serotonin synthesis, and combined with sertraline's reuptake inhibition, can cause excessive serotonergic activity. Cases of serotonin syndrome have been reported with this combination.

Recommendation: Avoid supplemental L-tryptophan while taking sertraline. Dietary tryptophan from food is generally safe. If already taking both, discontinue L-tryptophan and inform your prescriber.

SeriousCaution

Fluoxetine

L-Tryptophan supplementation increases serotonin synthesis, and combined with fluoxetine's potent, long-lasting serotonin reuptake inhibition, can produce excessive serotonergic activity. Early case reports of this combination documented agitation, restlessness, and other serotonin syndrome symptoms.

Recommendation: Avoid supplemental L-tryptophan with fluoxetine. This was one of the first reported SSRI-supplement serotonin syndrome interactions. Dietary tryptophan from food is not a concern.

SeriousCaution

Escitalopram

L-Tryptophan increases serotonin synthesis as its biosynthetic precursor. Combined with escitalopram's selective serotonin reuptake inhibition, the resulting increase in both serotonin production and synaptic retention can trigger serotonin syndrome.

Recommendation: Avoid supplemental L-tryptophan while taking escitalopram. If you wish to support mood through diet, discuss safe options with your prescriber.

DangerousContraindicated

MAOIs

L-Tryptophan feeds serotonin synthesis while MAOIs reduce serotonin breakdown, increasing risk of serotonin syndrome.

Recommendation: Do NOT combine L-tryptophan with MAOIs unless specifically directed and monitored by the prescriber managing the MAOI.

DangerousContraindicated

Phenelzine

L-Tryptophan feeds serotonin synthesis while Phenelzine reduces serotonin breakdown, increasing risk of serotonin syndrome.

Recommendation: Do NOT combine L-tryptophan with Phenelzine unless specifically directed and monitored by the prescriber managing Phenelzine.

Search all 24 interaction records for L-Tryptophan →

Sources

Sources, by evidence tier.

Numbered references. Citations throughout the page link here.

Meta-analyses & systematic reviews

7

Randomized controlled trials

2

Reviews & position papers

7

Reference material

1
Keep exploring

Deep dives & adjacent profiles.

Goal hubSleepGoal hubStress & Anxiety
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