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L-Tryptophan
Sole dietary precursor to serotonin and melatonin, studied for sleep onset and as an add-on to antidepressants.
What the evidence says
Tryptophan appears to help in 3 of 3 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 1970–2026 with a typical study size of 210 participants.
Based on 137 studies · 11 meta-analyses · 102 RCTs · 23,483 total participants
Confidence
High confidenceWhat the studies found
By outcome
Moderate 5.5 reflects a meta-analysis showing tryptophan ≥1g shortens night waking, a review of 40 controlled studies on sleep onset and add-on antidepressant evidence, tempered by mostly indirect depletion/kynurenine evidence rather than direct supplementation RCTs.
44 trials ongoing or recruiting · 99 completed on ClinicalTrials.gov
22 of the completed trials have posted results
Registered trials show research momentum for Tryptophan, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Tryptophan meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Not authorised by EFSA
“Tryptophan Helps to a normal sleep Helps to get a restful sleep Contributes to maintain nervous balance”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
L-Tryptophan is an essential amino acid that the body cannot produce, requiring dietary intake. It's the sole precursor to serotonin (the 'feel-good' neurotransmitter) and subsequently melatonin (the sleep hormone). Unlike 5-HTP, tryptophan is one step earlier in the synthesis pathway.
Converts to serotonin, supporting mood and well-being
Serotonin is further converted to melatonin for sleep
Can also be converted to niacin (vitamin B3)
How Tryptophan works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Consult healthcare provider; limited data
Start with lower doses; may be more sensitive to sedation
Risk of serotonin syndrome, do not combine without the prescriber. SSRI labels list tryptophan among the serotonergic drugs that raise it, and the phenelzine (MAOI) label lists L-tryptophan as a contraindication after reports of toxic reactions
May enhance sedative effects
Serotonergic opioid — combining with tryptophan raises serotonin syndrome risk
Serotonergic migraine drugs (e.g. sumatriptan) — additive serotonin effect raises serotonin syndrome risk
Raised risk of serotonin syndrome: the fluvoxamine label lists tryptophan among the drugs that increase it, and severe vomiting has been reported with the combination
Tip: Take only before bed; reduce dose if excessive
Tip: Take with a small amount of food
Tryptophan has an evidence score of 5.5/10 — moderate evidence based on 137 indexed studies, including 8 meta-analyses. Sole dietary precursor to serotonin and melatonin, studied for sleep onset and as an add-on to antidepressants. Representative study: PMID 40314175.
The commonly studied dose of Tryptophan is 500-1000 mg before bed. The cited sleep meta-analysis found the benefit mainly at 1 g a day or more. Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Tryptophan is before bed. It can be taken on an empty stomach. L-Tryptophan is the rarest essential amino acid and the sole precursor to serotonin and melatonin.
Tryptophan has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. The most commonly reported side effects are drowsiness, nausea. Use caution if any of these apply to you: Taking SSRIs, SNRIs, or MAOIs (serotonin syndrome risk); Eosinophilia-myalgia syndrome history.
5-HTP
Too few graded studiesDirect serotonin precursor that may support mood, sleep, and appetite control, but requires caution with certain medications.
Magnesium
Mixed evidenceSupports 300+ enzymatic reactions — critical for sleep, stress response, muscle function, and cognitive health.
L-Theanine
Too few graded studiesTea-derived amino acid that boosts alpha brain waves for calm, focused alertness — synergizes with caffeine to reduce jitteriness.
GABA
Too few graded studiesInhibitory neurotransmitter that calms neural activity — may work through the gut-brain axis for acute anxiety and sleep support.
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Reviewed by Dr. Baher Al Hakim · Last reviewed May 2026 · evidence from 137 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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