L-Theanine for Anxiety
L-theanine shows modest, short-term promise for calming everyday stress and subclinical tension in healthy adults, but the evidence is weak and it has not been shown to treat diagnosed anxiety disorders. It is not a substitute for standard anxiety care.
Why this grade7-layer evidence engine
This earns a Weak (Tier C) grade because the supportive evidence sits almost entirely in healthy or moderately stressed people, not in people with diagnosed anxiety. Small short-term RCTs found that 200-400 mg/day, or even a single 200 mg dose, lowered perceived stress, state/trait anxiety scores, and salivary cortisol (PMID 38758503, PMID 34562208, PMID 31623400), and two systematic reviews leaned positive for stress and anxiety symptoms (PMID 39633316, PMID 31758301).
The crucial caveat is the gap between feeling stressed and a clinical diagnosis. The single trial in DSM-5 generalized anxiety disorder added L-theanine to antidepressants and did not beat placebo on the main HAM-A anxiety measure (PMID 30580081, p=0.73). Trials are also small (largest n=46), doses range widely with no clear dose-response, no review pooled a quantitative effect, and several positive trials were industry-funded, which is why the engine flags weak, mixed evidence.
Authorities reinforce caution rather than endorsement. The US FDA treats L-theanine as generally recognized as safe but backs safety only, not any anxiety claim, while the EU's EFSA concluded a cause-and-effect relationship has not been established for its proposed mental-health benefits. The Cleveland Clinic says it may promote relaxation without drowsiness yet should not replace standard treatment, and major bodies like the NIH, Mayo Clinic, and Harvard offer no dedicated endorsement.
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 = 0.455
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (2 篇 > 0 negative)
- tier_strict_requirement_check — Tier 條件達標，未降階
- detect_disputes — 偵測到 0 個 hard + 1 個 soft dispute
- decide_status — 依 tier + dispute 結果決定 status