L-Tyrosine for Cognitive Function
L-tyrosine is not a general brain booster: it only restores working memory and mental flexibility that have been blunted by acute, catecholamine-depleting stressors such as sleep loss, cold, or heavy multitasking, and it does nothing for cognition in rested, unstressed people.
Why this grade7-layer evidence engine
This earns a B (Preliminary Evidence), published with a warning, because the human data are real but narrow and weak. Two systematic reviews anchor the case: Jongkees et al. 2015 (PMID 25797188) found tyrosine loading acutely counteracts drops in working memory and information processing under demanding conditions, with no benefit when conditions are easy, and a 2015 rapid evidence assessment (PMID 26126245) reported that every included study showed a positive effect for cognitive stress mitigation, but only enough to support a weak recommendation.
The evidence base is thin and conditional, which caps the grade. Studies are mostly small, acute, single-dose trials, and the response is not uniform: an RCT (PMID 27403851) showed benefits to working memory and inhibitory control depended on DRD2 genotype, while a small anorexia RCT (PMID 29735813, n=19) improved reaction time only in an already depleted clinical group. There is no long-term or large-population data.
Authorities reinforce the caution. EFSA accepts tyrosine as a precursor for catecholamine and dopamine synthesis but specifically rejected 'increased attention' claims, and the UK NHS says it cannot recommend supplementation given inadequate efficacy and safety data. No major clinic (Mayo, Cleveland, Harvard) endorses it for cognition. A drug-interaction warning also applies, notably with MAO inhibitors and levodopa.
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 = 0.58
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高階證據未達主導 (0 positive vs 1 negative)，由 raw_score 決定
- 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