Moderate evidence supports anxiety or acute stress response, sleep quality, and pediatric attention effects. Cognition, caffeine-combination effects, and immune-focused claims look more mixed or thinner under the current grading system than older summaries suggested. The branded Suntheanine form still has no convincing head-to-head edge over generic L-theanine.
Each row is a different health effect. A means the support looks strongest, B likely helpful, C mixed or modest, and — not enough human evidence yet.
Papers are individual studies. Research reviews summarize evidence from multiple studies, such as systematic reviews and meta-analyses.
Dose, form and timing based on trials in the database.
Products that pass third-party quality testing.
Product quality data coming soon
Product recommendations are being built from USP Verified, NSF Certified, and Labdoor test data. Products will only appear here after the supplement itself clears the evidence bar above — and only if the product passes third-party purity testing.
Grades come from 32 unique research papers indexed from PubMed — including 3 meta-analyses, 2 systematic reviews, and 15 randomized trials. Forty-seven of 64 health-effect records were rated low-confidence, primarily because L-theanine has many acute-dose trials and bundled-product abstracts (caffeine combinations and sleep/stress nutraceuticals) where the standalone L-theanine effect cannot always be cleanly attributed. Each supplement is graded by health effect using a certainty × effect matrix applied across PubMed evidence per health effect. Cochrane reviews and high-quality systematic reviews carry the most weight. From abstract-only data, "high certainty" is rare — most A grades come from moderate certainty plus consistent meaningful-positive evidence. See Methodology for full detail.
Read the full methodology → · Download all 32 citations (PDF)