Categories & Effectiveness

Cognition

Attention & Focus

7/10

Strong evidence of effectiveness

Neuroprotection & Plasticity

7/10

Strong evidence of effectiveness

Working & Long-term Memory

4/10

Moderate evidence of effectiveness

Energy

Metabolism Boost (Thermogenesis, Glucose Stability)

4/10

Moderate evidence of effectiveness

Mitochondrial ATP Production

4/10

Moderate evidence of effectiveness

Mood

Anxiety / Stress Reduction

4/10

Moderate evidence of effectiveness

Dosage & Side Effects

Recommended Dosage

Typical effective doses often involve consuming 200-400 mg of L-theanine daily, or specific amounts like 2 grams of matcha powder daily, as seen in studies. While optimal doses vary, exceeding safe limits, particularly for concentrated extracts like EGCG (suggested safe adult intake below 338 mg/day), can increase risks. Caution is advised for pregnant or breastfeeding individuals, children, the elderly, and those with pre-existing health conditions, who should consult a healthcare provider.

Potential Side Effects

Common side effects can include gastrointestinal discomfort, especially when green tea or its extracts are taken on an empty stomach. High doses or prolonged use of concentrated green tea extracts, particularly EGCG, have been linked to potential liver toxicity (hepatotoxicity). Individuals taking medications, especially those with a narrow therapeutic index, should be cautious due to potential interactions; consult your doctor before combining green tea extracts with other drugs.

Bioavailability & Half-Life

The absorption and utilization (bioavailability) of green tea's beneficial polyphenols, like EGCG, can be variable and present challenges, impacting how much effectively reaches the bloodstream and brain after consumption. Factors like individual metabolism and consumption patterns influence how quickly these compounds peak in the body and how long their effects last, though specific half-life details vary between components like L-theanine and EGCG. Research continues to explore ways to improve the bioavailability of these valuable green tea constituents.

Interactions & Stacks

Green tea components L-theanine and caffeine are often stacked together synergistically, as studies show their combination offers greater cognitive benefits than either substance alone. Caution should be exercised when combining green tea extracts with drugs that have a narrow therapeutic index or those metabolized by similar liver pathways, due to potential interactions. User reports and systematic reviews consistently highlight the L-theanine/caffeine combination for enhancing attention and cognitive performance.

Benefits by Use Case

Enhance Focus & Attention

Improves attention and reduces reaction time, particularly noted with L-theanine or the combination of L-theanine and caffeine. Effects may be most noticeable during demanding cognitive tasks.

Reduce Stress & Anxiety

L-theanine supplementation (200-400mg/day) may help reduce stress and anxiety responses in stressful situations. Consistent intake might be needed for sustained benefits.

Support Memory

Shows potential benefits for working memory and attention, which can indirectly support overall memory function. Effects on long-term memory consolidation are less consistently demonstrated.

Promote Brain Health

Offers neuroprotective effects through antioxidant and anti-inflammatory actions, potentially aiding against age-related decline and amyloid stress. Long-term, consistent consumption is likely key for these benefits.

Improve Mood & Social Acuity

May improve mood and the ability to perceive facial emotions (social acuity), contributing to better social interaction. Some studies also note a trend towards improved sleep quality.

Mechanism of Action

Green tea exerts its effects through multiple bioactive compounds, primarily polyphenols like EGCG and the amino acid L-theanine. EGCG acts as a potent antioxidant and anti-inflammatory agent, protecting cells from damage, inhibiting amyloid stress linked to neurodegeneration, and potentially modulating cell cycles and protein structure. L-theanine influences brain function by promoting relaxation without drowsiness, potentially by affecting neurotransmitter systems involved in mood and stress response, and synergizes with caffeine to enhance attention and working memory. Together, these components contribute to neuroprotection, support mitochondrial energy production, promote axonal growth, and modulate brain activity patterns associated with cognition.

Frequently Asked Questions

Is green tea good for focus?

Can green tea help with stress and anxiety?

Is green tea safe to take daily?

When is the best time to take green tea?

Does green tea interact with medications?

Can green tea improve memory?

What is EGCG?

What is L-theanine?

Summary & Expert Opinion

Green tea is a well-researched beverage with established benefits for cognitive function, mood, and overall brain health, largely attributed to its key components like L-theanine and EGCG. Its strengths lie in the synergistic effects of its compounds, particularly L-theanine and caffeine for attention, and the antioxidant and neuroprotective properties of EGCG. However, the bioavailability of some components can be limited, and high doses of extracts carry potential risks, mainly liver toxicity. Green tea or its components may be beneficial for individuals seeking gentle support for focus, stress reduction, and long-term brain health. Those sensitive to caffeine, pregnant or breastfeeding individuals, or those taking certain medications should exercise caution or consult a healthcare professional before using concentrated green tea supplements.

Research Studies

Showing 5 of 13 studies

Green Tea (Camellia sinensis): A Review of Its Phytochemistry, Pharmacology, and Toxicology (2022)

anticancer antioxidant metabolic effects +2 more

Authors:

Chao Li, Shuai Wang, Tiantian Zhao, Xinqiang Song

Findings:

This review systematically summarizes green tea's phytochemistry (polyphenols like EGCG, alkaloids, amino acids, polysaccharides, etc.) and pharmacology. Key findings indicate diverse activities including antioxidant, anticancer, hypoglycemic, antibacterial, antiviral, and neuroprotective effects, suggesting potential roles in managing conditions like diabetes, Alzheimer's disease, and cancer. However, high doses, particularly of extracts/EGCG, raise concerns about hepatotoxicity and DNA damage.

Participants:

Review covers studies using various models: in vitro (human cell lines like HeLa, HT-29, NCI-N87, SHSY-5Y; pig ovarian cells; bovine DNA), in vivo (mice, rats, dogs), and discusses human relevance (e.g., diabetes, AD, cancer patients; cautions for pregnancy, children, elderly). Specific strains/conditions mentioned (e.g., BALB/c, ICR, aging, diabetic, PD models).

Dosage:

Review cites numerous dose-dependent effects from various studies (in vitro/in vivo) using extracts, polyphenols, or specific compounds like EGCG. Examples range widely (e.g., µg/mL to mg/mL in vitro; mg/kg to g/kg in vivo). A No Observed Adverse Effect Level (NOAEL) of 2000 mg/kg/day for green tea catechins in rats and a suggested safe adult intake below 338 mg EGCG/day are mentioned. High doses (e.g., 1500 mg/kg EGCG in mice) linked to hepatotoxicity.

Study Quality Assessment:

This is a systematic review citing numerous experimental (in vitro, in vivo) studies and other reviews. Methods for literature search (PubMed, Google Scholar, Web of Science, CNKI) and inclusion/exclusion criteria are stated. Specific assays mentioned (DPPH, TOSC, flow cytometry, EIA, Ames test). Limitations acknowledged include research primarily being preclinical, challenges in clinical translation, limited toxicological data, and bioavailability issues with polyphenols. Funding sources for the review are disclosed (National Natural Science Foundation of China, Henan Province projects, Xinyang Normal University).

All Effects:

anticancer antioxidant metabolic effects neuroprotection toxicity

Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study (2021)

attention executive functions reaction time +1 more

Authors:

Shun Inagaki, Yoshitake Baba

Findings:

A single dose of l-theanine reduced reaction time in attention tasks (Stroop test) and improved working memory performance (increased correct answers, decreased omission errors in 4-Part CPT). The study suggests l-theanine may improve attention, working memory, and executive functions.

Participants:

Japanese men and women aged 50-69 years with Mini Mental State Examination-Japanese version score of 24 or higher.

Dosage:

Evaluations performed after a single dose and after 12 weeks of regular intake (specific mg dosage not mentioned).

Study Quality Assessment:

Double-blind, randomized, placebo-controlled study. Cognitive function assessed using Cognitrax test battery. Evaluations performed before intervention, after a single dose, and after 12 weeks of intake. Clinical Trial No.: UMIN000033812. Conflict of interest statement provided: Sponsor (ITO EN, Ltd.) covered testing costs and provided test food; specific roles of CRO and statistical analysis company mentioned.

All Effects:

attention executive functions reaction time working memory

The Cognitive-Enhancing Outcomes of Caffeine and L-theanine: A Systematic Review (2021)

Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis

Effects of Heat-Treated Green Tea Extract on Memory Function and ...

Green Tea ( Camellia sinensis ): A Review of Its Phytochemistry ...

Green tea catechin, epigallocatechin-3-gallate (EGCG)

EGCG potency catechins polyphenols

Green tea effects on cognition, mood and human brain function: A systematic review

anxiety reduction attention brain function +2 more

Findings:

Reviewed studies showed evidence that green tea influences psychopathological symptoms (e.g., anxiety reduction), cognition (e.g., benefits in memory and attention), and brain function (e.g., activation of working memory via fMRI). Beneficial cognitive effects were observed with the combined influence of caffeine and l-theanine, with lesser impact from separate administration.

Participants:

Humans

Study Quality Assessment:

Systematic review of 21 studies (4 randomised controlled trials, 12 cross-over studies, 4 cross-sectional studies, 1 cohort study). Quality assessed using adapted DELPHI-list (average score 8.06/9) and adapted Newcastle-Ottawa assessment scale (average score 6.7/9). Structured according to PRISMA statement. MeSH terms include 'Randomized Controlled Trials as Topic'.

All Effects:

anxiety reduction attention brain function cognition memory

Matcha Green Tea on Cognitive Functions: A Systematic Review ...

cognitive function emotional perception sleep quality +1 more

Findings:

Daily consumption of 2g matcha for 12 months led to significant improvements in social acuity score (perception of facial emotions). Primary cognitive outcomes (Montreal Cognitive Assessment, Alzheimer's Disease Cooperative Study Activity of Daily Living scores) showed no significant changes. A trend toward improvement in sleep quality (Pittsburgh Sleep Quality Index scores) was observed. Regular matcha consumption could improve emotional perception and sleep quality in older adults with mild cognitive decline.

Participants:

Ninety-nine older adults (N=99), including 64 with subjective cognitive decline and 35 with mild cognitive impairment.

Dosage:

2 g of matcha daily for 12 months.

Study Quality Assessment:

Randomized controlled trial (RCT), double-blind, placebo-controlled, N=99, duration 12 months. Participants stratified by age at baseline and APOE genotype. Analysis using mixed-effects model. Specific cognitive tests (perception of facial emotions, Montreal Cognitive Assessment, Alzheimer's Disease Cooperative Study Activity of Daily Living) and sleep quality measure (Pittsburgh Sleep Quality Index) used. Competing interests disclosed (authors employed by MCBI Inc. and ITO EN, LTD.). Stated 'no external funding'.

All Effects:

cognitive function emotional perception sleep quality social acuity

Synergistic effects of epigallocatechin gallate and l-theanine in nerve repair and regeneration by anti-amyloid damage, promoting metabolism, and nourishing nerve cells

anti-amyloid anti-inflammatory axonal growth +2 more

Findings:

The combination of EGCG and L-theanine demonstrated synergistic effects in protecting differentiated PC12 nerve cells against Aβ25–35-induced damage. This synergy involved inhibiting amyloid stress and inflammation, promoting metabolism (including mitochondrial activity and energy production), regulating the cell cycle towards quiescence (increased G0/G1 phase, decreased cyclins), promoting axonal growth (increased GAP43), and maintaining protein structural fidelity. These findings suggest EGCG + L-theanine promotes nerve cell repair and regeneration.

Participants:

In vitro study using an Alzheimer's Disease (AD) model established with Aβ25–35-induced differentiated neural cell line PC12 cells (Rat pheochromocytoma cell line). RNA sequencing data compared against Rattus norvegicus reference.

Dosage:

Cell experiments used final concentrations of 50 μM Aβ25–35 alone or co-incubated with 50 μM EGCG, 50 μM L-theanine, or both 50 μM EGCG + 50 μM L-theanine. Preliminary tests showed EGCG cytotoxicity at 100 μM and L-theanine growth promotion up to 100 μM.

Study Quality Assessment:

Original Research article published in Front. Nutr. Methods mentioned: MTT assay, ThT fluorescence detection, Transmission Electron Microscopy (TEM), Flow cytometry (cell cycle, apoptosis), Fourier Transform Infrared Spectroscopy (FTIR), JC-1 staining (mitochondrial membrane potential), DAPI staining, LDH cytotoxicity assay, ATP detection, Western blotting, Enzyme-linked immunosorbent assay (ELISA), BODIPY fluorescent staining, RNA sequencing (RNA-seq). Statistical analysis: one-way ANOVA with Turkey’s multiple comparison test (p < 0.05, p < 0.01). Funding sources listed. Conflict of interest statement included. Data availability mentioned (NCBI BioSample database, accession SAMN29216840).

All Effects:

anti-amyloid anti-inflammatory axonal growth cell cycle regulation neuroprotection

The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review

anxiety reduction cognition mood +1 more

Findings:

The review suggests that L-theanine (L-THE) supplementation may assist in reducing stress and anxiety in people exposed to stressful conditions. However, longer-term and larger studies are needed to clinically justify its use as a therapeutic agent.

Participants:

People exposed to stressful conditions (from human trials reviewed)

Dosage:

200-400 mg/day

Study Quality Assessment:

Systematic review following PRISMA checklist, based on 9 peer-reviewed human randomised controlled trials where L-THE supplement was compared to a control. Acknowledges need for longer-term and larger cohort studies.

All Effects:

anxiety reduction cognition mood stress reduction

The effects of tea (Camellia sinensis) or its bioactive compounds L-theanine or L-theanine plus caffeine on cognition, sleep, and mood in healthy participants: a systematic review and meta-analysis of rand

Toxicological effects of Camellia sinensis (green tea): A review

gastrointestinal disorders hepatotoxicity side effects

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Categories & Effectiveness

Cognition

Attention & Focus

Neuroprotection & Plasticity

Working & Long-term Memory

Energy

Metabolism Boost (Thermogenesis, Glucose Stability)

Mitochondrial ATP Production

Mood

Anxiety / Stress Reduction

Dosage & Side Effects

Recommended Dosage

Potential Side Effects

Bioavailability & Half-Life

Interactions & Stacks

Benefits by Use Case

Enhance Focus & Attention

Reduce Stress & Anxiety

Support Memory

Promote Brain Health

Improve Mood & Social Acuity

Mechanism of Action

Frequently Asked Questions

Summary & Expert Opinion

Research Studies

Green Tea (Camellia sinensis): A Review of Its Phytochemistry, Pharmacology, and Toxicology (2022)

Authors:

Findings:

Participants:

Dosage:

Study Quality Assessment:

All Effects:

Effects of l-Theanine on Cognitive Function in Middle-Aged and Older Subjects: A Randomized Placebo-Controlled Study (2021)

Authors:

Findings:

Participants:

Dosage:

Study Quality Assessment:

All Effects:

The Cognitive-Enhancing Outcomes of Caffeine and L-theanine: A Systematic Review (2021)

Authors:

Study Quality Assessment:

Acute effects of tea constituents L-theanine, caffeine, and epigallocatechin gallate on cognitive function and mood: a systematic review and meta-analysis

Participants:

Study Quality Assessment:

Effects of Heat-Treated Green Tea Extract on Memory Function and ...

Green Tea ( Camellia sinensis ): A Review of Its Phytochemistry ...

Green tea catechin, epigallocatechin-3-gallate (EGCG)

Findings:

Green tea effects on cognition, mood and human brain function: A systematic review

Findings:

Participants:

Study Quality Assessment:

All Effects:

Matcha Green Tea on Cognitive Functions: A Systematic Review ...

Findings:

Participants:

Dosage:

Study Quality Assessment:

All Effects:

Synergistic effects of epigallocatechin gallate and l-theanine in nerve repair and regeneration by anti-amyloid damage, promoting metabolism, and nourishing nerve cells

Findings:

Participants:

Dosage:

Study Quality Assessment:

All Effects:

The Effects of Green Tea Amino Acid L-Theanine Consumption on the Ability to Manage Stress and Anxiety Levels: a Systematic Review

Findings:

Participants:

Dosage:

Study Quality Assessment:

All Effects:

The effects of tea (Camellia sinensis) or its bioactive compounds L-theanine or L-theanine plus caffeine on cognition, sleep, and mood in healthy participants: a systematic review and meta-analysis of rand

Participants:

Study Quality Assessment:

Toxicological effects of Camellia sinensis (green tea): A review

Findings:

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