Protocol
L-Theanine 200 mg/day
L-theanine is an amino acid from tea.
Grade C: human trials exist, but they are small, mixed or not yet repeated. This is not a finding that it does not work. How to read a grade →
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How this letter has changedLatest: October 2026 · Corrected.
The protocol was named for 200 mg taken 30 to 60 minutes before sleep. Hidese et al. (Nutrients, 2019; PMID PubMed ID: the permanent number the US National Library of Medicine gives a published paper. Each one links to that paper's record on PubMed. 31623400) gave 200 mg a day for four weeks with no stated time, and the Bulman et al. meta-analysis A study that pools the numbers from several trials into one combined estimate. (Sleep Med Rev, 2025; PMID 40056718) pools trials of varied timing, mostly inside combination products. No trial tested the bedtime timing in the name, so the name now states the dose studied, L-Theanine 200 mg/day. Letter unchanged at C. Decided October 2026 by editor adjudication (Arnold Sandlow, D.C.).PMID 31623400 PMID 40056718
The L-theanine 200 mg sleep protocol held a B on Hidese et al. (Nutrients 2019; PMID 31623400), a 30-person crossover A trial design in which each participant receives both the treatment and the comparison, one after the other, and serves as their own control. trial of stress in which sleep quality was a secondary, self-reported outcome, funded by the company that makes the L-theanine tested. The review it cited as confirmation (Gerolymos et al., Mol Psychiatry 2026; PMID 42410082) does not pool sleep outcomes. The sleep meta-analysis (Bulman et al., Sleep Med Rev 2025; PMID 40056718) is positive on self-report only and pools combination products. One small unreplicated trial is C. Editor adjudication, October 2026.PMID 31623400 PMID 42410082 PMID 40056718
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This protocol is L-theanine, an amino acid from tea, at 200 mg a day. In the one study of this dose alone that measured sleep, 30 healthy adults reported better sleep, but sleep was not the main thing studied. The maker of the product paid for it. A review of 19 studies found small gains in reported sleep, mostly from products that mixed several ingredients.
L-theanine is an amino acid from tea. The cited trials gave 200 mg a day; none tested a time of day, so the protocol is named for the dose studied and not for a bedtime timing. The one trial of 200 mg/day alone that measured sleep (Hidese 2019, PMID 31623400, 30 adults, crossover) found better self-reported sleep quality as a secondary outcome; it was funded by the company that makes the L-theanine tested. A 2025 meta-analysis found small effects on self-reported sleep only, pooling trials that mostly tested combination products.
Why this gradeGrade C, small or unreplicated trials. The reasoning, and what the grade does not cover.
Grade C on self-reported sleep. The one trial of 200 mg/day alone that measured sleep, a crossover in 30 healthy adults, found the Pittsburgh Sleep Quality Index improved as a secondary outcome; it was funded by the company that makes the L-theanine tested (Hidese et al., 2019; PMID 31623400). A meta-analysis of 19 trials found small effects on self-reported sleep, mostly from combination products (Bulman et al., 2025; PMID 40056718).
WHAT THIS GRADE DOES NOT COVERobjectively measured sleep, such as sleep studies or actigraphy; any time of day, which no cited trial compared (the protocol was renamed to the dose studied in October 2026); combination products; and stress or anxiety outcomes.
A grade describes the human evidence for a named use. It is not advice, and it is not a judgment on any individual prescription. How the letters are decided →
The evidence, in fullThree papers, each linked to its PubMed record.
Hidese et al. (Nutrients, 2019; PMID 31623400): randomized placebo-controlled crossover, 30 healthy adults, 200 mg/day for 4 weeks; stress-related symptoms improved and the Pittsburgh Sleep Quality Index, a secondary outcome, improved. Funded by the company that makes the L-theanine tested. Bulman et al. (Sleep Med Rev, 2025; PMID 40056718): systematic review A review that searches for every study on a question using a method set in advance, then assesses them together. and meta-analysis of 19 randomized trials, 897 participants; small effects on self-reported sleep onset and quality only, with most trials testing L-theanine inside combination products. Gerolymos et al. (Mol Psychiatry, 2026; PMID 42410082): meta-analysis of 31 randomized trials of cognitive and affective effects; it does not pool sleep outcomes and is context, not sleep evidence.
Sleep onset latency and subjective sleep quality using a daily sleep diary at baseline and 4 weeks. For anxiety applications, use the GAD-7 or STAI at baseline and 4 weeks. L-theanine is often combined with caffeine: if used this way, track both alertness and jitteriness to confirm the intended ratio effect.
Evidence notes: not independently replicated The same finding reproduced by a separate research group. A result seen once can be chance or bias; a replicated one is harder to explain away., randomized trial, meta-analysis
Endpoint The outcome a trial measures to decide whether the treatment worked, such as heart attacks, blood pressure or a symptom score. graded: Self-reported sleep quality (self_report)
Last reviewed: July 2026
Educational use only · Not medical advice · EBL grades published human evidence and does not recommend treatment. Stopping a prescription is a decision for your physician.
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theanine[tiab] AND sleep[tiab] AND (randomized controlled trial[pt] OR meta-analysis[pt])Grades move when new trials publish. A free monthly email lists every grade EBL moved, with the reason and the trial behind it: the sign-up is on the Evidence Log →