Green Tea
TheaceaeCamellia sinensis
Also known as: Cha, Lu Cha, Matcha (powdered)
clinical_notes Clinical Summary
Green tea (Camellia sinensis) is a widely consumed beverage and concentrated-extract phytomedicine rich in polyphenolic catechins, especially EGCG, with robust evidence for cardiovascular, metabolic, and chemopreventive benefits.
While traditional brewed tea has an excellent safety profile, high-dose green tea extracts (>800 mg EGCG/day) have been linked to idiosyncratic hepatotoxicity, particularly in HLA-B*35:01 carriers.
Clinicians should differentiate between beverage use (safe) and concentrated supplement use (requires liver enzyme monitoring and drug-interaction screening, especially with β-blockers and warfarin).
Pregnancy Safety
Moderate caffeine intake (≤200 mg/day total) generally considered acceptable; higher intake linked to low birth weight and increased miscarriage risk. High-dose EGCG extracts should be avoided during pregnancy due to potential folate metabolism interference.
Lactation Safety
Caffeine transfers to breast milk; moderate tea consumption compatible with breastfeeding, but excessive intake may cause infant irritability and poor sleep. Avoid concentrated extracts.
warning Contraindications
- Concurrent use with high-dose green tea extract supplements (>800 mg/day EGCG) (avoid)Clinically Proven
- Iron-deficiency anemia (caution)Clinically Proven
- Warfarin therapy (caution)Clinically Proven
- Anxiety disorders / arrhythmia (caffeine sensitivity) (caution)Clinically Proven
- Nadolol therapy (and other β-blockers) (avoid)Clinically Proven
vital_signs Clinical Profile
Primary Indications
- check_circle Cardiovascular disease prevention
- check_circle Hyperlipidemia
- check_circle Metabolic syndrome
- check_circle Obesity
- check_circle Cognitive decline
- check_circle Type 2 diabetes
- check_circle Cancer chemoprevention (prostate, breast, colon)
- check_circle Dental caries prevention
- check_circle Fatigue
Therapeutic Actions
System Affinities
- check_circle Cardiovascular
- check_circle Nervous system
- check_circle Metabolic
- check_circle Hepatic
- check_circle Immune
labs Active Constituents
Catechins
Caffeine
L-theanine
Theaflavins
Thearubigins
Flavonols
Theobromine
Theophylline
Gallic acid
Tannins
history_edu Traditional Use
Traditional Chinese Medicine (TCM)
綠茶 (Lü Chá)
Nature: cool
- Clears Heat
- Promotes urination
- Resolves phlegm
- Sobers the mind (alleviates fatigue and drowsiness)
- Generates fluids
- Aids digestion (food stagnation)
Tea is one of the oldest documented medicinal plants in TCM. Classical texts attribute to tea the ability to 'lighten the body and sharpen the mind'. Traditionally used to counter greasy foods and to alleviate heat-related headaches.
Traditional Uses Across Healing Systems
While many herbs lack controlled clinical trials, centuries of traditional practice across cultures provide valuable insight into their therapeutic applications.
Clears Heat, resolves phlegm, aids digestion of greasy foods, alleviates fatigue and mental heaviness
Lu Yu's Cha Jing is considered the world's first monograph on tea.
Used for headache relief and to balance heating herbs; incorporated into dietary therapy
Matcha (powdered green tea) is central to Japanese tea ceremony (chanoyu).
Adopted as a mild stimulant and digestive (secondary to native herbs)
Used in Indian Assam and Darjeeling tea cultivation; widely consumed as a daily beverage.
Adopted as a cardiovascular tonic, antioxidant, and weight-management support
Green tea was introduced to the West via trade routes; 20th century research popularized catechins.
spa Parts Used
leaf
- Cardiovascular disease prevention
- Hyperlipidemia
- Weight management
- Cancer chemoprevention
- Cognitive function
Young leaves are steamed (Japanese sencha) or pan-fired (Chinese lu cha) immediately after picking to prevent oxidation, preserving catechins. Water temperature of 70-80°C (not boiling) yields optimal polyphenol extraction without excessive bitterness.
shield Safety
Contraindications — Evidence Basis
Concurrent use with high-dose green tea extract supplements (>800 mg/day EGCG)
Cumulative EGCG intake >800 mg/day from supplements has been associated with idiosyncratic hepatotoxicity; strongly linked to HLA-B*35:01 allele.
Iron-deficiency anemia
Tannins and catechins inhibit non-heme iron absorption; separate tea consumption from iron-rich meals or iron supplements by at least 1-2 hours.
Warfarin therapy
Green tea contains vitamin K and large volumes may antagonize warfarin; documented case report of reduced INR.
Anxiety disorders / arrhythmia (caffeine sensitivity)
Caffeine content (20-45 mg per cup) may exacerbate anxiety, insomnia, palpitations.
Nadolol therapy (and other β-blockers)
Green tea catechins markedly decrease nadolol plasma concentrations and blunt antihypertensive effect via OATP1A2 inhibition.
Monitoring Parameters
Monitor during use, especially with prolonged or high-dose therapy.
Liver enzymes (ALT, AST, ALP, bilirubin)
Baseline and at 3, 6, and 12 months when using EGCG extracts ≥400 mg/dayMonitor for idiosyncratic hepatotoxicity which has been reported at EGCG doses as low as 140 mg/day; most cases involve HLA-B*35:01 genotype.
flagThreshold: ALT >3× upper limit of normal: discontinue extract and investigate.
INR (in patients on warfarin)
Check within 1-2 weeks of starting or stopping high green tea intakeVitamin K content may antagonize warfarin; documented case of INR reduction.
flagThreshold: INR outside therapeutic range: adjust warfarin dose and counsel on consistent tea intake.
Ferritin and hemoglobin (iron status)
Baseline and every 6 months in at-risk individuals (menstruating women, vegetarians)Tannins substantially reduce non-heme iron absorption with chronic high intake.
flagThreshold: Ferritin <30 ng/mL: recommend separating tea from iron sources by 1-2 hours.
Toxicity
EGCG hepatotoxicity reported from cumulative doses as low as 140 mg/day with substantial interindividual variability; most cases involved supplements containing ≥800 mg/day EGCG.
Acute hepatitis (jaundice, elevated transaminases, fatigue, nausea); in severe cases, acute liver failure requiring transplantation. Caffeine overdose: tachycardia, tremor, insomnia, agitation.
Immediate discontinuation of green tea extract; supportive care with N-acetylcysteine in acute liver injury; liver function monitoring. Evaluate for HLA-B*35:01 genotype in idiosyncratic DILI cases.
Adverse Effects
CYP Metabolism
EGCG inhibits CYP3A4, CYP2B6, CYP1A2 in vitro at high concentrations; generally minimal clinical impact from beverage consumption. Green tea catechins inhibit OATP1A2 and OATP2B1 transporters, reducing oral bioavailability of nadolol, rosuvastatin, and fexofenadine. Caffeine metabolized by CYP1A2.
swap_horiz Interactions
Warfarin
Class: Anticoagulant (vitamin K antagonist)
Dried green tea leaves contain substantial vitamin K1 (phylloquinone); chronic high-volume consumption provides enough dietary vitamin K to antagonize warfarin, reducing INR. A case report described a 44-year-old man whose INR dropped from 3.79 to 1.14 after consuming 0.5-1 gallon/day of green tea; INR normalized after cessation.
Patients on warfarin should maintain consistent green tea intake (small, stable amounts acceptable); avoid sudden increases to large volumes. Monitor INR within 1 week of dietary changes. Concentrated green tea extracts contain minimal vitamin K and are less problematic for anticoagulation.
Nadolol
Class: Beta-blocker / antihypertensive
Green tea catechins (EGCG, ECG) inhibit intestinal organic anion transporting polypeptides OATP1A2 and OATP2B1, blocking nadolol uptake. Clinical study demonstrated up to 85% reduction in nadolol plasma exposure with concomitant green tea, with attenuation of BP-lowering effect.
Avoid green tea within 4 hours of nadolol dose. Prefer alternative beta-blocker (metoprolol, atenolol) if patient consumes green tea regularly. Monitor BP and heart rate to confirm therapeutic effect.
Rosuvastatin
Class: HMG-CoA reductase inhibitor (statin)
Green tea catechins inhibit intestinal OATP1A2/2B1 transporters, reducing rosuvastatin absorption. Clinical pharmacokinetic study showed a ~20% reduction in rosuvastatin AUC with single-dose green tea extract, potentially attenuating LDL-lowering.
Separate rosuvastatin administration from green tea by at least 4 hours. Monitor LDL-C response; consider atorvastatin as alternative if response is suboptimal.
Lisinopril
Class: ACE inhibitor / antihypertensive
Green tea catechin ingestion reduced lisinopril bioavailability by approximately two-thirds (66%) in healthy volunteers, likely via OATP1A2 inhibition and interference with intestinal absorption.
Advise separation of lisinopril from green tea by >4 hours, or consider an alternative ACE inhibitor administered on empty stomach. Monitor BP response.
Tacrolimus
Class: Calcineurin inhibitor / immunosuppressant
Green tea catechins inhibit both CYP3A and P-glycoprotein, reducing tacrolimus first-pass metabolism and efflux. Case reports describe elevated tacrolimus trough concentrations with concurrent green tea consumption — potentially causing nephrotoxicity and neurotoxicity given narrow therapeutic index.
Advise transplant patients to avoid green tea extracts and limit beverage consumption to small, consistent amounts. Monitor tacrolimus troughs more frequently with dietary changes.
Iron salts (ferrous sulfate, ferrous gluconate)
Class: Iron supplement
Tannins in green tea form insoluble complexes with non-heme iron in the gut, reducing iron absorption by up to 60%. Clinically relevant in iron-deficiency anemia treatment.
Separate iron supplement administration from green tea by at least 2 hours (preferably 4 hours). Warn anemia patients to avoid drinking tea with iron-rich meals. Vitamin C co-administration can partly counteract the effect.
Bortezomib
Class: Proteasome inhibitor / antineoplastic
EGCG directly binds to the boronic acid pharmacophore of bortezomib, forming a covalent adduct that inactivates the drug. In vitro and animal studies show complete abrogation of bortezomib's anticancer activity by EGCG.
Patients receiving bortezomib or carfilzomib should strictly avoid green tea, matcha, and EGCG-containing supplements throughout treatment. Counsel explicitly at chemotherapy initiation.
Fexofenadine
Class: Antihistamine (H1-receptor antagonist)
Green tea catechins inhibit OATP1A2-mediated intestinal uptake of fexofenadine, reducing plasma exposure by approximately 70% in healthy volunteers. Clinically manifests as reduced antihistaminic efficacy.
Take fexofenadine with water, avoiding green tea for at least 4 hours around dosing. Consider alternative antihistamines (cetirizine, loratadine) for regular green tea consumers.
Stimulants (amphetamines, methylphenidate, pseudoephedrine)
Class: CNS stimulant / sympathomimetic
Caffeine in green tea (25-50 mg/cup) has additive sympathomimetic and CNS-stimulating effects with prescription stimulants and sympathomimetics, causing increased heart rate, BP, anxiety, and insomnia.
Limit green tea to 1-2 cups/day in patients on stimulant therapy. Consider decaffeinated green tea for antioxidant benefits without caffeine load.
hub Combinations
Synergistic pairings can enhance therapeutic outcomes, while knowing suitable substitutes helps when specific herbs are unavailable or contraindicated.
Synergistic Combinations
4Black Pepper
Limited EvidencePiperine enhances EGCG bioavailability by inhibiting glucuronidation and increasing intestinal absorption.
Preclinical pharmacokinetic studies show piperine increases EGCG plasma AUC.
L-theanine
Moderate EvidenceL-theanine (naturally present in green tea) counterbalances caffeine's jitteriness while enhancing focus; 'calm alertness' effect.
RCTs show improved attention and reduced mental fatigue with caffeine + L-theanine vs either alone.
Rhodiola
Limited EvidenceBoth support energy and cognitive performance; Rhodiola adds adaptogenic anti-fatigue activity while green tea provides alertness.
No direct RCTs of the combination, but mechanistic rationale supported.
Turmeric
Limited EvidenceEGCG and curcumin synergistically inhibit NF-κB and COX-2; combined chemopreventive effects in preclinical models.
Preclinical evidence of synergy in breast and prostate cancer cell lines.
Traditional Pairings
1Ginger
Traditional UseTraditional Asian tea blends combine green tea with ginger for digestive warmth and anti-nausea effects, balancing green tea's cool nature.
Traditional use; limited clinical data on the combination.
science Studies
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 Randomized Controlled Trials
Meta-AnalysisThis systematic review and meta-analysis synthesized 50 RCTs examining the effects of tea (Camellia sinensis), l-theanine, or l-theanine plus caffeine on cognition, mood, and sleep in healthy adults, searching Cochrane, Embase, and Ovid Medline through August 2023. Fifteen studies contributed to at least one meta-analysis; l-theanine combined with caffeine significantly improved simple reaction time in the first and second hours post-intake compared to placebo. L-theanine alone improved relaxation and mood outcomes across multiple studies. The review concludes that Camellia sinensis bioactive compounds produce clinically meaningful cognitive and mood benefits with a favorable safety profile, supporting green tea use for brain fog and mental performance.
The effect of green tea (Camellia sinensis) on lipid profiles and renal function in people with type 2 diabetes and nephropathy: a randomized controlled clinical trial
RCTThis randomized controlled clinical trial examined the effect of green tea (Camellia sinensis) supplementation on lipid profiles and renal function markers in patients with type 2 diabetes mellitus (T2DM) and diabetic nephropathy. Participants in the intervention group received green tea supplementation over the study period, with outcomes including serum lipid levels (total cholesterol, LDL, HDL, triglycerides) and kidney function markers compared to a control group. The study provides direct clinical evidence on the cardiometabolic and nephroprotective potential of green tea in a high-risk diabetic population. The results contribute to understanding green tea's therapeutic role as a complementary intervention in T2DM management.
medication Dosing
tea
1-2 g dried leaf per 150 mL water (brewed at 70-80°C for 3-5 min)
3-5 cups daily
Avoid brewing with boiling water; steep shorter for milder taste. Each cup provides ~50-100 mg catechins and 20-45 mg caffeine.
capsule
250-500 mg standardized extract (50-90% polyphenols, ≥40% EGCG)
1-2x/day with food
Total EGCG should not exceed 800 mg/day. Take with food to reduce hepatotoxicity risk; avoid fasting-state dosing.
tincture
2-4 mL (1:5 in 40% ethanol)
2-3x/day
Less common preparation; beverage or standardized extract preferred.
powder
1-2 g matcha powder whisked in 70°C water
1-2x/day
Matcha provides whole-leaf catechins plus higher L-theanine; contains ~60-80 mg caffeine per 2 g serving.
Disclaimer: This information is largely AI-generated and reviewed by human experts at Evara Health. It is intended for educational and clinical reference purposes only and should not replace professional medical advice.
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