L-TheanineNew

Reviewed Sep 29, 2026

As of September 2026, L-theanine — a non-protein amino acid from green tea (Camellia sinensis) — has one of the larger recent evidence bases among calming nootropics. A 2026 systematic review and meta-analysis of 31 randomized controlled trials (1,168 participants; Molecular Psychiatry) found that a single 200 mg dose taken 30–60 minutes before testing significantly improved choice reaction time (standardized mean difference [SMD] 0.51; 95% CI 0.25–0.77), indicating enhanced attention; acute perceived stress was modestly reduced (SMD 0.31), and an exploratory single-dose signal for lower depressive symptoms in healthy adults (SMD 0.69; 95% CI 0.13–1.25) was reported but warrants confirmation. For sleep, a 2025 meta-analysis of 19 trials (897 participants; Sleep Medicine Reviews) found small but statistically significant improvements in subjective sleep quality (SMD 0.43), daytime functioning (SMD 0.33) and sleep-onset latency (SMD 0.15), with little change in total sleep time — consistent with relaxation rather than sedation. A 2025 review of 50 RCTs (Nutrition Reviews) and a 2026 mini-review (Frontiers in Nutrition) converge on 100–400 mg supporting attention (especially combined with caffeine) and 200–450 mg/day supporting sleep. Across trials L-theanine has been well tolerated with no serious adverse events. These are small-to-moderate, population-level pooled effects that do not guarantee individual results. L-theanine is a dietary supplement, not a drug, and is not intended to diagnose, treat, cure or prevent any disease — discuss use with your physician, particularly if you take medication for blood pressure, mood or sleep.