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L-Tryptophan Side Effects & Safety

Evidence:Moderate
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This content is for informational purposes only and does not constitute medical advice. Statements about dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary — consult your healthcare provider before starting any supplement. Full disclaimer

Safety Profile

Overall safety rating: Safe with Caution

Potential Side Effects

  • Drowsiness — expected effect when used for sleep
  • Nausea or GI discomfort at higher doses
  • Headache or lightheadedness in some individuals
  • Dry mouth reported occasionally

Drug & Supplement Interactions

  • SSRIs and MAOIs — risk of serotonin syndrome when combined with serotonergic drugs; contraindicated with MAOIs
  • 5-HTP — avoid combining; both raise serotonin and can cause serotonin excess
  • Sedative medications — additive drowsiness
  • Carbidopa — may enhance tryptophan's conversion to serotonin peripherally

Maximum Dose

Do not exceed: 6 g/day has been used in clinical research; doses above 3 g may cause GI upset and drowsiness

Full L-Tryptophan Guide

References

  1. ReviewSilber BY, Schmitt JA. (2010). Effects of tryptophan loading on human cognition, mood, and sleep. Neuroscience & Biobehavioral Reviews. DOI PubMed
  2. RCTMurphy SE, Longhitano C, Ayres RE, et al. (2006). Tryptophan supplementation induces a positive bias in the processing of emotional material in healthy female volunteers. Psychopharmacology. DOI PubMed
  3. Meta-analysisOgawa S, Fujii T, Koga N, Hori H, et al. (2014). Plasma L-tryptophan concentration in major depressive disorder: new data and meta-analysis.. The Journal of clinical psychiatry. DOI PubMed
  4. Meta-analysisKikuchi AM, Tanabe A, Iwahori Y (2021). A systematic review of the effect of L-tryptophan supplementation on mood and emotional functioning.. Journal of dietary supplements. DOI PubMed
  5. ReviewCarneiro IBC, Toscano AE, Lacerda DC, da Cunha MSB, et al. (2018). L-tryptophan administration and increase in cerebral serotonin levels: Systematic review.. European journal of pharmacology. DOI PubMed
  6. Getirana-Mota M, Aidar FJ, de Souza RF, Brito CJ, et al. (2026). The Effect of L-Tryptophan Intake on Dynamic Strength in Paralympic Powerlifting.. International journal of tryptophan research : IJTR. DOI PubMed
  7. Khan S, Iqbal MZ, Solangi F, Azeem S, et al. (2025). Impact of amino acid supplementation on hydroponic lettuce (Lactuca sativa L.) growth and nutrient content.. Scientific reports. DOI PubMed
Show 3 more references
  1. Rueda GH, Causada-Calo N, Borojevic R, Nardelli A, et al. (2024). Oral tryptophan activates duodenal aryl hydrocarbon receptor in healthy subjects: a crossover randomized controlled trial.. American journal of physiology. Gastrointestinal and liver physiology. DOI PubMed
  2. Jiang L, Wang J, Xu L, Cai J, et al. (2022). Lactobacillus casei modulates inflammatory cytokines and metabolites during tuberculosis treatment: A post hoc randomized controlled trial.. Asia Pacific journal of clinical nutrition. DOI PubMed
  3. Ferguson C, Aisbett B, Lastella M, Roberts S, et al. (2022). Evening Whey Protein Intake, Rich in Tryptophan, and Sleep in Elite Male Australian Rules Football Players on Training and Nontraining Days.. International journal of sport nutrition and exercise metabolism. DOI PubMed