NutriDex

The Supplement Research Compendium
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L-Tryptophan

Essential amino acid and serotonin precursor used for sleep and mood.

Moderate evidence 🌙Sleep & Mood

✚ Updated · How we grade evidence

Evidence tier
Moderate
Research weight
Citations
7 verified / 7
Classification
Sleep & Mood
❝
What the evidence says. Graded moderate: a meta-analysis shows ≥1 g shortens wake-after-sleep-onset, and one good RCT helps premenstrual mood, but most sleep trials are small and other components (sleep latency, total time) are unchanged. Depression evidence is too thin to recommend, and a contamination-linked outbreak that killed dozens looms over its safety record. (Moderate evidence: Several controlled trials; effects real but modest or context-dependent.)

What is L-Tryptophan?

L-Tryptophan is a sleep and mood supplement used for reduce night-time waking. NutriDex grades the human evidence as Moderate. L-Tryptophan is an essential amino acid the body converts to 5-HTP and then serotonin and melatonin, which underlies its use for sleep and mood. A 2022 meta-analysis of randomized trials found doses of at least 1 g before bed shortened wake-after-sleep-onset by roughly 30 minutes, but did not reliably change how fast people fell asleep, total sleep time, or sleep efficiency. For mood, the strongest single trial showed 6 g/day eased premenstrual dysphoria (a 34.5% drop in mood scores vs 10.4% on placebo). Depletion studies confirm that removing tryptophan lowers serotonin and worsens mood in vulnerable people, supporting the mechanism. However, a 2002 meta-analysis of depression found only 2 of 108 trials were admissible, so antidepressant claims are unproven. Effects overall are modest and narrow, and a 1989 contamination outbreak that caused over 1,500 cases of eosinophilia-myalgia syndrome and 37+ deaths shadows its history.

Purported Benefits

✓Reduce night-time waking
✓Modest sleep-quality gains
✓Ease premenstrual mood symptoms
✓Supports serotonin synthesis

Evidence by outcome

The same supplement can be well-proven for one use and unproven for another — here is the human evidence graded outcome by outcome.

OutcomeEvidenceEffectStudies
Night-time waking (wake after sleep onset)Meta-analysis: >=1 g/night shortened WASO ~30 min; effect specific to staying asleep. Moderate ↑ benefit · moderate 1
Sleep latency / total sleep timeMeta-analysis found no reliable change in latency/total time; an older small trial showed reduced latency at 1 g. Mixed ↔ mixed · small 2
Premenstrual mood symptomsSingle RCT (n=71): 6 g/day cut premenstrual mood scores 34.5% vs 10.4% placebo; not replicated. Preliminary ↑ benefit · moderate 1
Depression treatmentOf 108 depression trials only 2 were admissible; authors judged evidence too weak to recommend. No Evidence ↔ mixed 1
Mood via serotonin precursor mechanismDepletion studies and a diet RCT confirm tryptophan affects mood, mainly in vulnerable individuals. Moderate ↑ benefit · small 2

Dosing & Compounds

Typical Dose
1–3 g taken 30–60 min before bed for sleep; mood trials used up to 6 g/day. Take away from high-protein meals, which block brain uptake.
Active Compounds
L-Tryptophan5-HTP (metabolite)Serotonin (downstream)

Safety & Cautions

Common effects are drowsiness, nausea, headache and dizziness; high doses can cause GI upset. The serious risk is serotonin syndrome when combined with SSRIs/SNRIs, MAO inhibitors, triptans, tramadol, or 5-HTP/St John's Wort, so avoid these combinations. It adds to sedatives, benzodiazepines and alcohol. Critically, a 1989 outbreak of eosinophilia-myalgia syndrome (1,500+ cases, 37+ deaths) was linked to contaminated batches, and rare post-ban cases persist, so use only pharmaceutical-grade product. Avoid in pregnancy, breastfeeding, and liver or kidney disease without medical advice. Educational only — always check with your doctor or pharmacist before combining L-Tryptophan with any medicine.

L-Tryptophan drug interactions

Known or theoretical interactions between L-Tryptophan and common medications — educational, not exhaustive. Always check with your doctor or pharmacist before combining L-Tryptophan with any medicine.

Avoid
SSRIs / SNRIs (sertraline, fluoxetine, venlafaxine)
Can cause serotonin syndrome: agitation, tremor, sweating, rapid heartbeat, high fever; can be life-threatening.
L-tryptophan is the dietary precursor to serotonin; added to SSRI/SNRI reuptake inhibition it drives excess CNS serotonin. MedlinePlus — Serotonin syndrome · NCCIH — Depression & Complementary Health Approaches
Avoid
MAOIs (phenelzine, tranylcypromine)
High risk of serotonin syndrome; combination can be dangerous. Do not combine.
MAOIs block serotonin breakdown while tryptophan supplies extra precursor, producing a dangerous excess of serotonin. MedlinePlus — Serotonin syndrome

Key Studies

Meta-analysis Sutanto 2022 ✓ Full text
Meta-analysis: Trp ≥1 g/night shortened wake-after-sleep-onset (~30 min) and improved subjective sleep quality; sleep latency and total time unchanged.
Meta-analysis Shaw 2002 ✓ PubMed
Of 108 depression trials, only 2 met quality criteria; pooled they beat placebo (OR 4.1) but authors deemed the evidence too weak to recommend.
RCT Lindseth 2015 ✓ PubMed
Crossover RCT (n=25): a high-tryptophan diet produced more positive affect and significantly less depression, irritability and anxiety than a low-tryptophan diet.
RCT Steinberg 1999 ✓ PubMed
RCT (n=71): L-tryptophan 6 g/day during the luteal phase cut premenstrual mood scores 34.5% vs 10.4% on placebo across 3 cycles.
RCT Hartmann 1979 ✓ PubMed
Controlled trial (n=15 mild insomniacs): 1 g L-tryptophan significantly cut sleep latency; lower doses trended the same way, within normal dietary intake.
Safety Allen 2011 ✓ PubMed
Case of L-tryptophan-induced eosinophilia-myalgia syndrome after the FDA lifted its ban; notes the 1989 epidemic traced to a single contaminated source.
Review Young 2013 ✓ PubMed
Review: lowering plasma tryptophan ~60%+ depresses mood mainly in those vulnerable to depression; supports serotonin precursor mechanism but not as sole cause.
7 sources cited · 7 verified Search all studies on PubMed ↗

Common questions about L-Tryptophan

What is L-Tryptophan used for?

L-Tryptophan is most often taken for Reduce night-time waking, Modest sleep-quality gains, Ease premenstrual mood symptoms, Supports serotonin synthesis. Essential amino acid and serotonin precursor used for sleep and mood.

Does L-Tryptophan work — what does the evidence say?

Moderate evidence. Several controlled trials; effects real but modest or context-dependent. L-Tryptophan is an essential amino acid the body converts to 5-HTP and then serotonin and melatonin, which underlies its use for sleep and mood. A 2022 meta-analysis of randomized trials found doses of at least 1 g before bed shortened wake-after-sleep-onset by roughly 30 minutes, but did not reliably change how fast people fell asleep, total sleep time, or sleep efficiency. For mood, the strongest single trial showed 6 g/day eased premenstrual dysphoria (a 34.5% drop in mood scores vs 10.4% on placebo). Depletion studies confirm that removing tryptophan lowers serotonin and worsens mood in vulnerable people, supporting the mechanism. However, a 2002 meta-analysis of depression found only 2 of 108 trials were admissible, so antidepressant claims are unproven. Effects overall are modest and narrow, and a 1989 contamination outbreak that caused over 1,500 cases of eosinophilia-myalgia syndrome and 37+ deaths shadows its history.

What is the typical dose of L-Tryptophan?

1–3 g taken 30–60 min before bed for sleep; mood trials used up to 6 g/day. Take away from high-protein meals, which block brain uptake.

Is L-Tryptophan safe? Any cautions or side effects?

Common effects are drowsiness, nausea, headache and dizziness; high doses can cause GI upset. The serious risk is serotonin syndrome when combined with SSRIs/SNRIs, MAO inhibitors, triptans, tramadol, or 5-HTP/St John's Wort, so avoid these combinations. It adds to sedatives, benzodiazepines and alcohol. Critically, a 1989 outbreak of eosinophilia-myalgia syndrome (1,500+ cases, 37+ deaths) was linked to contaminated batches, and rare post-ban cases persist, so use only pharmaceutical-grade product. Avoid in pregnancy, breastfeeding, and liver or kidney disease without medical advice.

How many studies support L-Tryptophan?

NutriDex cites 7 sources for L-Tryptophan, graded "Moderate".

Does L-Tryptophan interact with any medications?

Yes — known or theoretical interactions include: Antidepressants (SSRIs / SNRIs) (avoid), MAOI antidepressants (avoid). This is educational and not exhaustive; always check with your doctor or pharmacist before combining L-Tryptophan with any medicine.

Cite this page
APA

Peh, D. (2026). L-Tryptophan: Benefits, Dosage, Side Effects & Evidence. NutriDex — The Supplement Research Compendium. Retrieved 26 Jun 2026, from https://nutridex.info/s/l-tryptophan

BibTeX
@misc{nutridex_l_tryptophan,
  author       = {Peh, Daryl},
  title        = {L-Tryptophan: Benefits, Dosage, Side Effects \& Evidence},
  year         = {2026},
  howpublished = {NutriDex --- The Supplement Research Compendium},
  url          = {https://nutridex.info/s/l-tryptophan},
  note         = {Reviewed by Dr Daryl Peh, MBBS Singapore, MMed FM. Accessed 2026-06-26}
}

For medical claims, citing the underlying primary studies linked above is preferred. NutriDex is an educational reference, not medical advice.

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