L-Tryptophan for Depression
L-tryptophan supplements have only weak, outdated support for treating depression, and they are not an established therapy. The small positive signal comes from a handful of old, low-quality trials, while regulators and clinics stop short of endorsing it for mood.
Why this grade7-layer evidence engine
This earns a Weak (C) grade because the entire human evidence base is small and aged. The Shaw systematic review and meta-analysis (PMID 11687048, PMID 12169147) located 108 trials but found only 2 (64 patients total) of acceptable quality. Those pooled to a Peto odds ratio of 4.1, yet the confidence interval was very wide (95% CI 1.3-13.2) and the authors themselves judged the evidence insufficient due to tiny samples and likely publication bias.
Supporting data are thin and indirect. The only randomized trial here added tryptophan to fluoxetine in just 30 people and reported no p-values (PMID 11022398). A depletion review (PMID 11331552) shows that lowering tryptophan can worsen mood in already-treated patients, supporting a serotonergic mechanism, but it is not a treatment trial. No modern, high-quality RCTs exist; the evidence has essentially not been updated in over two decades.
Authorities reinforce the caution. The US FDA lists L-tryptophan only as a nutrient supplement, with a notable safety history (the 1989 eosinophilia-myalgia syndrome outbreak), and EFSA rejected mood-enhancement health claims for lack of a cause-and-effect relationship. The Cleveland Clinic notes only that low serotonin is associated with depression, without endorsing tryptophan as a treatment. There is also a real serotonin-syndrome risk when combined with antidepressants.
Scoring transparency
All scores computed by a 7-layer evidence engine — fully auditable▸View the full decision path (audit trail)
- compute_raw_score — 加權公式: L2×0.30 + L3×0.25 + L5×0.25 + L11×0.10 + L1×0.10 = 0.522
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 無高階證據可裁決
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 0 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status