アミノ酸臨床用量 · 100–200mg/day (trials pairing it with caffeine used roughly 1:1 to 1.7:1 theanine:caffeine)効果発現時間 · 30–60 minutes (acute)

L-Theanine

Name: L-Theanine — Human Clinical Effect Matrix
Creator: The Nootropic Lab
License: https://creativecommons.org/licenses/by/4.0/

A 2026 meta-analysis of 31 RCTs (n=1,168) found a single 200mg dose taken 30–60 minutes before testing improved choice reaction time; its acute stress effect was modest and driven by high-risk-of-bias studies, and anxiety effects were inconsistent. With caffeine, RCTs (Haskell et al., 2007; Kahathuduwa 2016) and an 11-RCT meta-analysis (Camfield 2014) show the combination beats either compound alone on attention and reaction time. The one alpha-wave (MEG) trial found higher alpha activity at 2 hours, and only in people with higher trait anxiety.

By The Nootropic Lab editorial teamUpdated 2026年10月9日8 min read✓ Fact-checked

エビデンス確認日: 2026年9月28日

作用機序

L-theanine is a non-protein amino acid found primarily in green tea. It crosses the blood-brain barrier and has been linked to increased alpha brain wave activity. It also modulates GABA, serotonin, and dopamine levels. Combined with caffeine, it improves attention measures more than either compound alone.

臨床エビデンスの概要

ヒト効果マトリクス

Based on human clinical trials only. Animal and in-vitro data excluded.

効果	エビデンス	効果の大きさ	研究数	備考
Calm Focus (Alpha Waves)	preliminary	小	1	White 2016 (n=34) found higher resting alpha activity 2 hours after dosing — not at 45 minutes — and only in participants with higher trait anxiety; it did not track subjective calm or cortisol.
Anxiety & Stress	mixed	小	2	The 2026 31-RCT meta-analysis found anxiety effects inconsistent and non-significant (except one 400mg/day clinical trial) and a modest acute stress effect driven by high-risk-of-bias studies; White 2016 found lower subjective stress 1 hour post-dose. Rogers 2008 found no acute anxiolytic effect at 200mg.
Sleep Quality	moderate	小	1	A 2025 meta-analysis (18 studies, n=897) found small improvements in subjective sleep latency, daytime dysfunction and sleep quality. No trial has tested it combined with magnesium.
Caffeine Synergy	strong	大	3	Haskell 2007, Kahathuduwa 2016 and an 11-RCT meta-analysis show the combination outperforms either compound alone on attention and reaction time; caffeine dose drove the effect more than theanine dose.

Evidence key: Strong = multiple consistent RCTs · Moderate = smaller/fewer RCTs · Preliminary = early trials or small n · Mixed = conflicting results

実証された効果

Faster reaction time after a single 200mg dose
Better attention with caffeine than caffeine alone
Small improvements in subjective sleep quality

副作用と注意事項

Extremely well tolerated — no serious adverse events across a 31-RCT meta-analysis
Possible mild sedation at high doses
Generally considered very safe

摂取方法

Dosage100–200mg per dose

Timing30 minutes before your cognitive work session or 30 minutes before caffeine

With foodNo significant food interaction. Can be taken on an empty stomach. Absorption is reliable regardless of meal timing.

FormsCapsule or powder. Suntheanine is the most studied branded L-Theanine (from enzymatic synthesis, identical to tea-derived theanine). Bulk L-Theanine powder dissolves in water but is subtly sweet and easy to mix.

スタッキングの推奨

L-Theanineと相性の良い成分とその理由。

Caffeine

The most studied nootropic stack. Trials used 200–250mg theanine with 150–160mg caffeine (roughly 1:1 to 1.7:1). The combination improved attention and reaction time more than either alone; in a controlled trial (Rogers 2008) theanine did not significantly reduce caffeine jitteriness. This pairing is found in virtually every quality pre-work stack.

Bacopa Monnieri

Both have anxiolytic properties working via different mechanisms. L-Theanine provides immediate calm; Bacopa builds sustained stress tolerance over weeks. A gentle, non-sedating anxiety-reduction combination.

Ashwagandha

Both target stress through distinct pathways (GABA modulation for theanine; HPA axis for ashwagandha). Good daytime anxiety stack without sedation.

よくある質問

What is the ideal ratio of L-Theanine to caffeine?

No trial has established an ideal ratio. The positive combination trials used roughly 1:1 to 1.7:1 theanine to caffeine — for example 250mg theanine with 150mg caffeine (Haskell 2007) and 200mg with 160mg (Kahathuduwa 2016). A meta-analysis found the caffeine dose drove the effect more than the theanine dose.

Does L-Theanine work without caffeine?

Partly. On its own, a single 200mg dose improved choice reaction time in a 2026 meta-analysis of 31 RCTs, but anxiety effects were inconsistent and the one alpha-wave trial found an effect only in people with higher trait anxiety. It's not stimulating on its own.

Is it safe to take L-Theanine every day?

Yes. Green tea contains theanine and has been consumed daily for millennia without toxicity concerns. No tolerance develops. Chronic daily use is both safe and effective. No cycling required.

Why take a supplement when I can just drink green tea?

A standard cup of green tea contains ~25–50mg of L-Theanine — well below the 100–200mg therapeutic dose. You would need 4–8 cups of green tea to match a single supplement dose, along with a significant caffeine load. Supplements allow precise dosing without unwanted caffeine.

Can L-Theanine help with sleep if taken at night?

Modestly. A 2025 meta-analysis (18 studies, n=897) found small improvements in subjective sleep onset latency, daytime dysfunction and overall sleep quality. It doesn't cause sedation. Combinations with magnesium are popular but have not been tested in a trial.

Top stacks containing L-Theanine

Mind Lab Pro

9.4/10

Opti-Nutra

Editor's Choice

NooCube

7.6/10

Wolfson Brands

L-Theanine in Japan

L-theanine has an established presence in Japan's Foods with Function Claims system. A Consumer Affairs Agency verification report tags multiple L-theanine notifications 「食添」 in its ingredient-category column, and one such notification, Kyowa Co.'s D295 「ヘルススイッチ睡眠」, carries the CAA-recorded claim wording: "本品はL-テアニンを含みます。L-テアニンは起床時の疲労感や眠気の軽減をサポートすることが報告されています。また、L-テアニンは一過性の作業などによるストレス（精神的負担）を和らげる機能が報告されています。" Multiple other L-theanine notifications with sleep- and stress-related claims appear in the same report, indicating L-theanine has been notified as a functional ingredient more than once in Japan.

L-theanine's FFC notification record

The Consumer Affairs Agency's own FY2019 Foods with Function Claims verification report tags multiple L-theanine notifications 「食添」 in its ingredient-category column, alongside the notified functional ingredient name "L-テアニン". One entry, notification D295 for Kyowa Co.'s 「ヘルススイッチ睡眠」, records the notified claim text verbatim, covering both a morning-fatigue/drowsiness claim and a transient work-stress-relief claim tied to L-theanine intake. The same report lists further L-theanine notifications from multiple manufacturers across the document, showing L-theanine has been notified as a functional ingredient more than once in Japan's Foods with Function Claims system.

Products in Japan

Consumer Affairs Agency (FFC)

Can L-theanine be sold as a food ingredient in Japan?

Yes. The Consumer Affairs Agency's own verification report tags L-theanine notifications 「食添」 and records multiple Foods with Function Claims notifications built around "L-テアニン" as the functional ingredient, including Kyowa Co.'s D295 「ヘルススイッチ睡眠」 notification, which the same report lists across several manufacturers and product formats.

What functional claims has L-theanine carried in Japanese notifications?

Per the CAA-recorded text for notification D295, L-theanine has carried a claim that it supports reducing morning fatigue and drowsiness ("起床時の疲労感や眠気の軽減をサポートする") and eases transient work-related stress — claims specific to that notified product, not a general effect established for the ingredient itself.

Prefecture guides

Sources: CAA — H31年度機能性表示食品検証報告書 (FY2019 Foods with Function Claims verification report) · CAA — H31年度機能性表示食品検証報告書, existing-food-additive tag on L-theanine notifications

Regulatory note

本ページは教育目的の編集コンテンツであり、医学的助言を構成するものではありません。日本国内で販売される機能性表示食品（FFC）および特定保健用食品（FOSHU）は、消費者庁への届出または許可を必要とします。届出のない輸入品については、日本の薬機法（旧薬事法）の下で疾病治療を示唆する表現は規制されます。サプリメントを開始する前に、必ず資格のある医療専門家にご相談ください。This page is editorial and not medical advice. Foods with Function Claims (FFC) and Foods for Specified Health Uses (FOSHU) sold in Japan require notification or approval from the Consumer Affairs Agency. Imported products without notification cannot make disease-treatment claims under the Pharmaceuticals and Medical Devices (PMD) Act. Note: In July 2026, the Consumer Affairs Agency (CAA) opened a public comment period (Notice No. 235080088, closes 30 July 2026) on proposed revisions to permitted claim wording for FFC-notified ingredients including DHA, phosphatidylserine, and NMN; compliant claim language may require updating once the final Cabinet Office Order is published. Consult a qualified healthcare professional before starting any supplement.

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