L-Theanine for Sleep Quality
L-theanine appears to produce a small improvement in self-reported sleep quality and time to fall asleep in healthy adults, but the effect is modest, rests largely on subjective ratings, and is not established for diagnosed insomnia.
Why this grade7-layer evidence engine
The preliminary (B) grade reflects evidence that points in a consistent direction but with small effect sizes. A 2025 meta-analysis of 18 trials (PMID 40056718, n=897) found statistically significant gains in subjective sleep quality (SMD 0.43), sleep-onset latency (SMD 0.15), and daytime dysfunction (SMD 0.33), and a 2026 systematic review (PMID 41176609) judged 200-450 mg/day safe and effective for healthy sleepers. These effects are small, with wide confidence intervals and notable heterogeneity.
Two limits keep this from a stronger grade. The benefit shows up on subjective questionnaires more than objective recordings: a matcha trial supplying only about 50 mg of theanine (PMID 39275223) found no change in EEG-measured sleep. Several supportive trials also tested combination products rather than theanine alone, including a casein-peptide blend (PMID 35277011) and a multi-ingredient formula (PMID 36094342), so the isolated effect is hard to separate, and one pooled analysis (PMID 40314930) reported no clear sleep-specific signal.
Authorities remain cautious. The FDA grants only food-safety (GRAS) status with no efficacy claim, and the EU's EFSA concluded that a cause-and-effect relationship has not been established. Mayo Clinic notes there 'aren't enough clinical studies,' while Cleveland Clinic says it 'may help' but calls the human evidence preliminary. With no quality trials in clinical insomnia, this is best seen as a mild sleep-support aid, not a treatment.
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 = 0.621
- tier_from_score — 依分數區間映射至 tier letter
- apply_hec_rules — 高品質 SR/MA 顯示 positive (1 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