The Facts On Green Tea!

Can green tea help you lose weight, improve performance, lower cholesterol, treat diarrhea, and more? Find out if it is right for you!

Also Known As: Chinese Tea

Scientific Names: Camellia sinensis

Uses (evidence-based)

  • Supports weight loss and the maintenance of a healthy weight (using green tea extract standardized to 25% EGCG).1
  • May improve cognitive performance.2
  • Supports healthy cholesterol levels.3
  • Associated with a lower risk of breast, bladder, esophageal and pancreatic cancers.4,5
  • Reduces the duration and severity of diarrhea.6
  • Associated with a lower risk of Parkinson's disease.7
Caffeine in green tea may prevent adenosine's inhibition of dopaminergic transmission. Thus allowing for more dopamine, which plays a role in the clinical symptoms of Parkinson's disease.
"Caffeine in green tea may prevent adenosine's inhibition of dopaminergic transmission. Thus allowing for more dopamine, which plays a role in the clinical symptoms of Parkinson's disease."

Mechanism Of Action

Green tea extracts rich in EGCG (epigallocatechin gallate) are thought to increase calorie and fat metabolism.8 Antioxidant polyphenols (epigallocatechin gallate or EGCG, epigallocatechin or EGC, epicatechin gallate or ECG) are thought to be associated with a reduced risk of atherosclerosis and heart disease.9

EGCG is thought to be responsible for reducing risk of cancer. The possible mechanism is the prevention of new blood vessel growth in tumors (so essentially you starve the tumor).10

Research shows that polyphenols in green tea can produce antidiarrheal effects.6

Caffeine in green tea may prevent adenosine's inhibition of dopaminergic transmission, thus allowing for more dopamine, which plays a role in the clinical symptoms of Parkinson's disease.7

Side Effects

Common side effects with very large doses of green tea (exceeding 5 cups of green tea per day):

Green tea
  • Stomach upset
  • Constipation
  • Headache
  • Sweating
  • Anxiety
  • Nervousness
  • Insomnia
  • Restlessness
  • Agitation
  • Tremor
  • Irritability
  • Heart arrhythmias
  • Palpitations
  • Heartburn
  • Loss of appetite
  • Nausea
  • Vomiting
  • Diarrhea
  • Dizziness
  • Ringing in the ears
  • Elevated blood sugar
  • Elevated cholesterol
  • Liver toxicity
  • Convulsions

Note: Adverse effects of caffeine from green tea tend to be more severe in children than adults!

Site Guides Green Tea
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Interactions With Medications

  • Adenosine (used for irregular heart rhythm): Green tea inhibits action of adenosine.

  • Anticoagulant, antiplatelet agents (examples include Coumadin and aspirin): Green tea contains vitamin K and can make Coumadin (warfarin) ineffective or less effective.

    Aspirin: Green tea should not be taken if you are on aspirin, because they both prevent platelets from clotting. The use of green tea and aspirin together may increase your risk of bleeding.

  • Beta-lactam antibiotics (examples include cephalosporins and penicillins): Green tea may increase the effectiveness of beta-lactam antibiotics by reducing bacterial resistance to treatment.

  • Benzodiazepines (used for anxiety; examples include Valium and Ativan): Caffeine reduces the sedative effects of benzodiazepines.

  • Beta-blockers (examples include propranolol and metoprolol): Caffeine can increase blood pressure in people taking beta blockers.

  • Clozapine (used as an antipsychotic medication): Green tea can reduce the effectiveness of clozapine if green tea is taken less than 40 minutes before taking clozapine.

  • Ephedrine (used as bronchodilator, vasopressor, decongestant): Green tea and ephedrine together will increase the incidence of agitation, tremors, insomnia, and weight loss.

  • Lithium (for treatment of mania and depression): Green tea can reduce blood levels of lithium (a medication used to treat manic/depression).

  • Monoamine oxidase inhibitors (MAOIs) (used for treating depression; examples include phenelzine and tranylcypromine): Green tea and MAOIs taken together may cause hypertensive crisis (severe increase in blood pressure).

  • Oral contraceptives: Oral contraceptives and green tea may increase the effects of caffeine.

Dosages Used in The Research

  • 1 cup of tea per day was associated with cognitive performance.2
  • 10 cups or more were associated with lowered cholesterol levels.3
  • 3 or more cups per day were associated with a reduced risk of certain cancers.4
  • 5-33 cups of green tea daily were associated with a reduced risk of Parkinson's disease.7
  1. Chantre P, Lairon D. Recent findings of green tea extract AR25 (exolise) and its activity for the treatment of obesity. Phytomedicine 2002:9:3-8.
  2. Durlach PJ. The effects of a low dose caffeine on cognitive performance. Psychopharmacol 1998;140(1):116-9.
  3. Imai K. Nakachi K. Cross-sectional study of effects of drinking green tea on cardiovascular and liver diseases. BMJ 1995;310:693-696.
  4. Inoue M, Tajima K, Mizutani M, et al. Regular consumption of green tea and the risk of breast cancer recurrence: follow-up study from the Hospital-based Epidemiologic Research Program at Aichi Cancer Center (HERPACC), Japan. Cancer Lett 2001;167:175-82.
  5. Bushman JL. Green and cancer in human: a review of the literature. Nutr Cancer 1998;31(3):151-9.
  6. Schulz V, Hansel R, Tyler VE. Rational Phytotherapy: A Physician's Guide to Herbal Medicine. Terry C. Telger, trans. 3 rd ed. Berlin , GER:Springer, 1998.
  7. Ross GW, Abbott RD, Petrovitch H, et al. Association of coffee and caffeine intake with the risk of Parkinson disease. JAMA 2000;283:2674-9.
  8. Nemecz G. Green tea. US Pharmacist 2000;May:67-70.
  9. Graham HN, Green tea composition, consumption, and polyphenol chemistry. Prev Med 1992;21:334-50.
  10. Cao Y, Cao R. Angiogenesis inhibited by drinking tea. Nature 1999;398:381.

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