Tryptophan
Essential amino acid and serotonin precursor, taken for mood and sleep support.
Pharmacology
Contents
WHAT IS TRYPTOPHAN?
Detailed overview
Tryptophan is an essential, proteinogenic amino acid and the dietary precursor of serotonin and, downstream, melatonin. After crossing the blood-brain barrier via the large neutral amino acid transporter, it is converted by tryptophan hydroxylase to 5-hydroxytryptophan and then to serotonin, so its availability partly gates central serotonin synthesis. A 2002 Cochrane review found tryptophan and 5-HTP appeared better than placebo for depression, though it cautioned that trial quality was limited, and a 2022 meta-analysis reported improvements in sleep quality with supplementation. Because it competes with other large neutral amino acids for brain uptake, a light carbohydrate can raise its central availability by prompting insulin to clear competitors from the blood.
Mechanism
Serotonin precursor (via 5-HTP)
Evidence
Moderate (Cochrane review, sleep meta-analysis)
Legal status
Dietary supplement; Rx antidepressant adjunct in some countries
Receptor profile
- Tryptophan hydroxylase / serotonin synthesisStrong
- Melatonin synthesisModerate
- Large neutral amino acid transporter (LAT1)Moderate
- Kynurenine pathwayWeak
Safety
Side effects, stop signs, contraindications
Side effects · 5
- Drowsiness and sedation, especially at higher evening doses
- Nausea, stomach upset, occasionally diarrhea
- Dizziness, headache, dry mouth
- Risk of serotonin syndrome when combined with other serotonergic drugs (SSRIs, MAO inhibitors, triptans)
- Historical caution: the 1989 eosinophilia-myalgia syndrome (EMS) outbreak was traced to a contaminated manufacturing batch, not tryptophan itself
Contraindications · 4
- Concurrent SSRIs, SNRIs, MAO inhibitors or other serotonergic drugs: serotonin syndrome risk
- Pregnancy and breastfeeding: safety as a supplement is not well established, avoid
- Carcinoid syndrome or other conditions with serotonin overproduction
- Avoid before driving or operating machinery due to possible sedation
Related Nootropics
Same therapeutic category
Studies
Related research and clinical findings
Tryptophan and 5-hydroxytryptophan for depression
Shaw K, Turner J, Del Mar C
The impact of tryptophan supplementation on sleep quality: a systematic review, meta-analysis, and meta-regression
Sutanto CN, Loh WW, Kim JE
Can tryptophan supplement intake at breakfast enhance melatonin secretion at night?
Nagashima S, Yamashita M, Tojo C, Kondo M, Morita T, Wakamura T
A Perspective on the Safety of Supplemental Tryptophan Based on Its Metabolic Fates
Fernstrom JD
Effects and side effects associated with the non-nutritional use of tryptophan by humans
Fernstrom JD
Tryptophan supplementation and serotonin function: genetic variations in behavioural effects
Gibson EL
FAQ
FAQ
Essential amino acid and serotonin precursor, taken for mood and sleep support.
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Structure & chemistry
The information here is strictly for educational and scientific purposes. It does not replace medical advice or clinical consultation, and it does not encourage illegal substance or pharmaceutical use. Data is sourced. When in doubt, consult your doctor.