L-Theanine
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, an 11-study meta-analysis (Camfield 2014) found moderate effects versus placebo on alertness and attention-switching accuracy; Kahathuduwa 2016 found additive effects with no interaction, and Foxe 2012 found no added benefit over either compound alone. The one alpha-wave (MEG) trial found higher alpha activity at 2 hours, and only in people with higher trait anxiety.
Evidence reviewed:
Mechanism of action
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 improved attention measures versus placebo in several trials, though Foxe 2012 found no added benefit over either compound alone.
Clinical evidence summary
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, an 11-study meta-analysis (Camfield 2014) found moderate effects versus placebo on alertness and attention-switching accuracy; Kahathuduwa 2016 found additive effects with no interaction, and Foxe 2012 found no added benefit over either compound alone. The one alpha-wave (MEG) trial found higher alpha activity at 2 hours, and only in people with higher trait anxiety.
Human effect matrix
Based on human clinical trials only. Animal and in-vitro data excluded.
| Effect | Evidence | Magnitude | Studies |
|---|---|---|---|
| Calm Focus (Alpha Waves) | preliminary | Small | 1 |
| Anxiety & Stress | mixed | Small | 2 |
| Sleep Quality | moderate | Small | 1 |
| With Caffeine | moderate | Moderate | 4 |
Evidence key: Strong = multiple consistent RCTs · Moderate = smaller/fewer RCTs · Preliminary = early trials or small n · Mixed = conflicting results
Documented benefits
- Faster reaction time after a single 200mg dose
- Better attention with caffeine than with placebo in several trials
- Small improvements in subjective sleep quality
Side effects & cautions
- Extremely well tolerated — no serious adverse events across a 31-RCT meta-analysis
- Possible mild sedation at high doses
- Generally considered very safe
How to take
Stacking recommendations
Ingredients that pair well with L-Theanine and why.
The trials we cite used 50–250mg theanine with 40–250mg caffeine. Versus placebo, the combination improved attention measures in several trials, though Foxe 2012 found no added benefit over either compound alone; in a controlled trial (Rogers 2008) theanine did not significantly reduce caffeine jitteriness.
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.
Both target stress through distinct pathways (GABA modulation for theanine; HPA axis for ashwagandha). Good daytime anxiety stack without sedation.
Frequently asked questions
What is the ideal ratio of L-Theanine to caffeine?
No trial has established an ideal ratio. The positive combination trials used 97–250mg theanine with 40–160mg caffeine — for example 100mg theanine with 50mg caffeine (Owen 2008), 250mg with 150mg (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
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
- Mind Lab Pro7.5/10No FFC notification found (checked 2026-10-06)Local price: ≈ $69/month
- NooCube7/10No FFC notification found (checked 2026-10-06)Local price: ≈ $64.99/month
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.
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. Consult a qualified healthcare professional before starting any supplement.
Sources (11)expand
- PMID 42410082Cognitive and affective effects of L-Theanine: a systematic review and meta-analysis of 31 randomized trials (2026)
- PMID 24946991Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis (2014)
- PMID 18006208The effects of L-theanine, caffeine and their combination on cognition and mood (2007)
- PMID 26869148Acute effects of theanine, caffeine and theanine-caffeine combination on attention (2016)
- PMID 26797633Anti-Stress, Behavioural and Magnetoencephalography Effects of an L-Theanine-Based Nutrient Drink: A Randomised, Double-Blind, Placebo-Controlled, Crossover Trial (2016)
- PMID 40056718The effects of L-theanine consumption on sleep outcomes: A systematic review and meta-analysis (2025)
- PMID 17891480Time for tea: mood, blood pressure and cognitive performance effects of caffeine and theanine administered alone and together. (2008)
- PMID 18681988The combined effects of L-theanine and caffeine on cognitive performance and mood. (2008)
- PMID 21040626The combination of L-theanine and caffeine improves cognitive performance and increases subjective alertness. (2010)
- PMID 22326943Assessing the effects of caffeine and theanine on the maintenance of vigilance during a sustained attention task. (2012)
- PMID 25761837A double-blind, placebo-controlled study evaluating the effects of caffeine and L-theanine both alone and in combination on cerebral blood flow, cognition and mood. (2015)