Tryptophan
| Evidence Level: L5 | Predicted Indications: 8 |
Table of Contents
Tryptophan: From an Unspecified Original Indication to Insomnia
One-Sentence Summary
Tryptophan is an essential amino acid and precursor of serotonin and melatonin. The data compiled for this report do not list an approved original indication for it. The TxGNN model ranks restless legs syndrome as its top prediction, but the best-supported candidate is Insomnia, which has no registered clinical trials and 19 publications, mostly older small studies, reviews and preclinical work. Restless legs syndrome, the top-ranked prediction, has no registered clinical trials and 6 publications, only two of them older small clinical studies.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | Not available (the one US license on record has no indication text) |
| Predicted New Indication | Restless legs syndrome (rank 1 prediction); insomnia is the best-supported candidate (rank 4) |
| TxGNN Prediction Score | 99.72% (restless legs syndrome); 99.47% (insomnia) |
| Evidence Level | L3 (restless legs syndrome and insomnia); L4–L5 for the other candidates |
| US Market Status | Cancelled only |
| Number of NDAs | 1 (cancelled) |
| Recommended Decision | Hold |
Other predicted indications (all with TxGNN scores of 99.0–99.6%):
| Rank | Predicted Indication | Evidence Level | Decision |
|---|---|---|---|
| 2 | Primary hereditary glaucoma | L5 | Hold |
| 3 | Open-angle glaucoma | L4 | Hold |
| 5 | Methemoglobinemia | L5 | Hold |
| 6 | Methemoglobinemia, alpha type | L5 | Hold |
| 7 | Methemoglobin reductase deficiency | L5 | Hold |
| 8 | Congenital prothrombin deficiency | L5 | Hold |
Why is This Prediction Reasonable?
Detailed mechanism of action data is not available for this drug. Tryptophan is nonetheless well known as the dietary precursor of serotonin and melatonin, two molecules that regulate the sleep-wake cycle, mood and motor control. It also interacts with dopaminergic and iron-related pathways implicated in restless legs syndrome.
Restless legs syndrome: Two small studies from 1986–1987 examined L-tryptophan in restless legs syndrome and periodic leg movements. They have not been confirmed by modern randomized trials. Pharmacovigilance data show that serotonergic antidepressants can worsen restless legs syndrome, so the serotonin system appears to modulate symptoms in a complex, possibly bidirectional way.
Insomnia: The mechanistic rationale is strong because serotonin and melatonin regulate sleep. Older clinical studies (1983, 1987) tested L-tryptophan in chronic insomnia against placebo and hypnotics. A 2025 mouse study tested a tryptophan–fructooligosaccharide combination. The supplied data do not show that the American Academy of Sleep Medicine guideline recommends tryptophan.
Glaucoma: Literature reports altered tryptophan metabolism and serotonin levels in glaucoma patients, but these are associative biomarker findings and do not show that supplementation helps.
Methemoglobinemia and congenital prothrombin deficiency: These are computational predictions without supporting literature or a plausible mechanism in the supplied data.
Clinical Trial Evidence
Currently no related clinical trials are registered for any of the predicted indications.
Literature Evidence
Restless legs syndrome (top-ranked prediction)
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 3953904 | 1986 | Clinical study | Am J Psychiatry | L-tryptophan in the treatment of restless legs syndrome |
| 3659737 | 1987 | Clinical study | Sleep | Periodic leg movements with L-dopa, 5-hydroxytryptophan and L-tryptophan |
| 33836477 | 2021 | Systematic review/meta-analysis | Sleep Med Rev | Restless legs syndrome in chronic liver disease; elevated tryptophan is among the proposed contributors |
| 1305630 | 1992 | Review | Int J Neurosci | L-tryptophan in neuropsychiatric disorders |
| 36897462 | 2023 | Case series | Neurol Sci | Restless legs syndrome in DNAJC12 deficiency (hyperphenylalaninemia with deficient dopamine and serotonin signalling) |
| 32546134 | 2020 | Pharmacovigilance study | BMC Psychiatry | Antidepressants and movement disorders |
Insomnia (best-supported candidate)
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 6410442 | 1983 | Controlled clinical trial | Psychopharmacology | L-tryptophan (1 g) vs flurazepam, secobarbital and placebo in 96 serious insomniacs over 7 nights |
| 3432358 | 1987 | Clinical study | Pharmacopsychiatry | L-tryptophan 2 g plus varying sleeping times in 25 patients; 76% markedly improved after 4 weeks, but some relapsed afterwards |
| 27998379 | 2017 | Guideline | J Clin Sleep Med | AASM guideline on pharmacologic treatment of chronic insomnia (the supplied data do not show a tryptophan recommendation) |
| 33475068 | 2021 | Review | Comb Chem High Throughput Screen | Nutraceuticals for sleep disorders |
| 40681828 | 2025 | Review | Mol Neurobiol | Tryptophan metabolites and the kynurenine pathway in insomnia |
| 40772548 | 2025 | Preclinical (mouse) | Food Funct | Tryptophan–fructooligosaccharide combination improved sleep through anti-inflammation and gut microbiota modulation |
| 39779759 | 2025 | Bioinformatics | Sci Rep | Tryptophan metabolism gene CYP1B1 as a shared biomarker for Parkinson’s disease and insomnia |
Open-angle glaucoma
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 33963197 | 2021 | Metabolomic/observational | Sci Rep | Altered tryptophan metabolism and microglial inflammation in primary open-angle glaucoma |
| 19052654 | 2008 | Observational | Mol Vis | Serotonin levels in aqueous humor of glaucoma patients |
| 4069571 | 1985 | Observational | Ophthalmic Res | Amino acids, including tryptophan, were higher in aqueous humor of glaucoma patients than in cataract patients |
These glaucoma findings are associative only. Primary hereditary glaucoma and the three methemoglobinemia-related predictions have no supporting literature, apart from one indirect 1995 rat toxicology study (PMID 8533035) on methemoglobinemia, and congenital prothrombin deficiency has none.
US Market Information
| Authorization Number | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| Not available (cancelled) | Tryptophan (BioActive Nutritional, Inc.) | Liquid (also listed as solution/drops and spray) | Not available |
Safety Considerations
- Disease contraindication signals (knowledge graph, not label text): autoimmune disease, systemic lupus erythematosus (including pediatric), anxiety disorder, neurotic disorder, dysthymic disorder, schizophrenia, phenylketonuria and other disorders of phenylalanine metabolism, and eosinophilia-myalgia syndrome (including the form associated with tryptophan).
- Historical concern: Eosinophilia-myalgia syndrome was linked in 1989 to contaminated L-tryptophan products, and the literature describes the contamination as arising in production. This history, together with the cancelled US market status, warrants caution.
- Drug interactions: 17 interactions were identified.
- Major (9): lorcaserin, dolasetron, palonosetron, ondansetron, fenfluramine, granisetron, sibutramine, methylene blue, doxepin (oral and topical), procarbazine. Most of these involve additive serotonergic effects.
- Moderate (6): morphine, codeine, hydrocodone, cyproheptadine, ozanimod, ifosfamide.
Please refer to the package insert for label warnings and contraindications; these were not available for this report.
Conclusion and Next Steps
Decision: Hold
Rationale: The top prediction, restless legs syndrome, rests on two small studies from the 1980s with no modern RCTs or registered trials. Insomnia has the strongest rationale and some older controlled data, but the evidence is dated, no trials are registered, the US market status is cancelled only, and L-tryptophan carries a historical safety concern (eosinophilia-myalgia syndrome). The other predictions are model outputs without credible supporting evidence. Insomnia and restless legs syndrome may be framed as research questions at best.
To proceed, the following is needed:
- FDA package insert warnings and contraindications (a blocking gap for safety screening)
- Mechanism of action data
- A systematic review of the 1980s tryptophan trials in insomnia and restless legs syndrome
- A modern, adequately powered randomized trial with pharmaceutical-grade tryptophan
- A safety plan covering eosinophilia-myalgia syndrome, product purity and serotonergic drug interactions
- Clarification of the regulatory pathway, given that the only US license is cancelled
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.