Tryptophan
| Evidence Level: L3 | Predicted Indications: 8 |
Table of Contents
- Tryptophan
Tryptophan: From Nutritional/Supplement Use to Restless Legs Syndrome
One-Sentence Summary
Tryptophan is an essential amino acid and the precursor of serotonin and melatonin. It is marketed in Canada as single-ingredient products and as a component of parenteral nutrition amino acid solutions. The TxGNN model predicts it may be effective for restless legs syndrome, but there are no registered clinical trials and only 6 publications. Most are indirect, and the two direct clinical reports date from 1986 and 1987.
Quick Overview
| Item | Content |
|---|---|
| Original Indication | No approved indication text is available in the Canadian licence records |
| Predicted New Indication | Restless legs syndrome |
| TxGNN Prediction Score | 0.9972 |
| Evidence Level | L3 |
| Canada Market Status | Marketed (marketed DINs on record: at least 19; cancelled: 1) |
| Number of DINs | at least 20 |
| Recommended Decision | Hold |
Why is This Prediction Reasonable?
Currently, detailed mechanism of action data is not available from the data compiled for this report. Based on known biology, tryptophan is the precursor of serotonin and melatonin. Both are involved in sleep-wake regulation and motor control, so it may be mechanistically applicable to restless legs syndrome (RLS).
RLS is thought to involve dopaminergic dysfunction and iron dysregulation, with possible serotonergic modulation of motor and sleep circuits. Two older clinical studies (1986 and 1987) examined L-tryptophan in RLS and periodic leg movements. A review of tryptophan in neuropsychiatric disorders also discusses serotonin’s role in movement disorders.
The direction of effect is uncertain. Serotonergic antidepressants have been linked to RLS and movement-disorder reports in a pharmacovigilance study. Increasing serotonin precursor availability could therefore help or worsen symptoms. The evidence is old, small, and not confirmed by modern trials.
Clinical Trial Evidence
Currently no related clinical trials registered.
Literature Evidence
| PMID | Year | Type | Journal | Key Findings |
|---|---|---|---|---|
| 3953904 | 1986 | Clinical study (small, uncontrolled or early-phase) | Am J Psychiatry | L-tryptophan examined as a treatment for restless legs syndrome |
| 3659737 | 1987 | Clinical study | Sleep | Periodic leg movements studied with L-dopa, 5-hydroxytryptophan and L-tryptophan |
| 1305630 | 1992 | Review | Int J Neurosci | Review of serotonin’s role in neuropsychiatric conditions, including movement disorders such as akathisia |
| 33836477 | 2021 | Systematic review/meta-analysis | Sleep Med Rev | RLS in chronic liver disease; elevated tryptophan, histamine and dopamine turnover and iron disturbances are discussed as contributing factors (indirect) |
| 36897462 | 2023 | Case series/genetic | Neurol Sci | RLS in DNAJC12 deficiency, which impairs dopamine and serotonin neurotransmission (indirect monoamine link) |
| 32546134 | 2020 | Pharmacovigilance study | BMC Psychiatry | Antidepressant-associated movement disorders; indirect and possibly in the opposite direction |
Canada Market Information
The records do not include dosage form or approved indication text. The main authorizations are:
| DIN | Product Name | Dosage Form | Approved Indication |
|---|---|---|---|
| 00654531 | TRYPTAN | Not listed | Not listed |
| 02239327 | TRYPTAN | Not listed | Not listed |
| 02458721 | APO-TRYPTOPHAN | Not listed | Not listed |
| 02240333 | TEVA-TRYPTOPHAN | Not listed | Not listed |
| 02046709 | CLINIMIX | Not listed | Not listed |
Other licences include further TRYPTAN, APO-TRYPTOPHAN, TEVA-TRYPTOPHAN, CLINIMIX and TRAVASOL products.
Safety Considerations
- Drug Interactions: 17 interactions were identified.
- Major: lorcaserin, dolasetron, palonosetron, ondansetron, fenfluramine, granisetron, sibutramine, methylene blue, doxepin (including topical), procarbazine. Most of these involve serotonergic mechanisms, so serotonin syndrome is a key concern.
- Moderate: morphine, codeine, hydrocodone, cyproheptadine, ozanimod, ifosfamide.
- Knowledge-graph contraindication signals (these come from a knowledge graph, not from label text): autoimmune disease, systemic lupus erythematosus (including paediatric), 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: The literature compiled for this report mentions eosinophilia-myalgia syndrome, which was linked to contaminated L-tryptophan production in 1989.
Please refer to the package insert for the full label warnings and contraindications.
Conclusion and Next Steps
Decision: Hold
Rationale: The prediction score is very high, but there are no registered trials. The only direct clinical evidence is two small, old studies from 1986 and 1987. The direction of effect is uncertain because serotonergic agents have been linked to RLS in other reports. The 17 interactions, several of them major, and the knowledge-graph contraindication signals also call for caution. Label safety data could not be obtained, which is a blocking gap for safety screening.
To proceed, the following is needed:
- Health Canada package insert warnings and contraindications (blocking gap)
- Detailed mechanism of action data
- Approved indication and dosage form data for the Canadian licences
- A modern, controlled study of tryptophan in RLS, with a review of the original 1986 and 1987 reports
- A safety plan covering serotonergic co-medications and the contraindication signals above
Other Predicted Indications (Brief)
The other predictions are weaker than restless legs syndrome and should stay on Hold.
| Predicted Indication | TxGNN Score | Evidence Level | Comment |
|---|---|---|---|
| Primary hereditary glaucoma | 0.9957 | L5 | No trials, no literature, no mechanistic rationale |
| Open-angle glaucoma | 0.9950 | L4 | Observational metabolomic associations only; direction of effect unknown |
| Insomnia | 0.9947 | L3 | Early studies from 1983 and 1987 (including a controlled comparison against flurazepam, secobarbital and placebo); no modern RCTs. Worth further research |
| Methemoglobinemia | 0.9930 | L5 | One indirect rat toxicology study; no plausible mechanism |
| Methemoglobinemia, alpha type | 0.9918 | L5 | Prediction only |
| Methemoglobin reductase deficiency | 0.9908 | L5 | Prediction only; standard therapy acts through different mechanisms |
| Congenital prothrombin deficiency | 0.9901 | L5 | Prediction only; no plausible mechanism |
Disclaimer
This content is for research purposes only and does not constitute medical advice. Clinical validation is required before any clinical application.