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Green Tea Safety and Side Effects

Green tea is safe for most adults. Green tea extract seems to be safe for most people for short-term use. In some people, green tea can cause stomach upset and constipation. Green tea extracts have been reported to cause liver problems.

Too much green tea, such as more than five cups per day, can cause side effects because of the caffeine. These side effects can range from mild to serious and include headache, nervousness, sleep problems, vomiting, diarrhea, irritability, irregular heartbeat, tremor, heartburn, dizziness, ringing in the ears, convulsions, and confusion. Green tea seems to reduce the absorption of iron from food.

If you are pregnant or breastfeeding, green tea in small amounts is probably not harmful. Do not drink more than 2 cups a day of green tea. This amount of tea provides about 200 mg of caffeine. Consuming more than this amount has been linked to an increased risk of miscarriage and other negative effects...

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What other names is Green Tea known by?

Benifuuki, Camellia sinensis, Camellia thea, Camellia theifera, Constituant Polyphénolique de Thé Vert, CPTV, EGCG, Epigallo Catechin Gallate, Épigallo-Catéchine Gallate, Epigallocatechin Gallate, Extrait de Camellia Sinensis, Extrait de Thé, Extrait de Thé Vert, Extrait de Thea Sinensis, Green Sencha Tea, Green Tea Extract, Green Tea Polyphenolic Fraction, GTP, GTPF, Japanese Sencha Green Tea, Japanese Tea, Kunecatechins, Poly E, Polyphenon E, PTV, Té Verde, Tea, Tea Extract, Tea Green, Thé, Thé de Camillia, Thé Japonais, Thé Vert, Thé Vert de Yame, Thé Vert Sensha, Thea bohea, Thea sinensis, Thea viridis, Yame Green Tea, Yabukita, Yame Tea.

What is Green Tea?

Green tea is made from the Camellia sinensis plant. The dried leaves and leaf buds of Camellia sinensis are used to produce various types of teas. Green tea is prepared by steaming and pan-frying these leaves and then drying them. Other teas such as black tea and oolong tea involve processes in which the leaves are fermented (black tea) or partially fermented (oolong tea).

Green tea is taken by mouth to improve mental alertness and thinking.

It is also taken by mouth for depression, non-alcoholic fatty liver disease (NAFLD), inflammatory bowel disease (ulcerative colitis or Crohn's disease), weight loss and to treat stomach disorders, vomiting, diarrhea, headaches, and bone loss (osteoporosis).

Some people take green tea by mouth to prevent various cancers, including breast cancer, prostate cancer, colon cancer, gastric cancer, lung cancer, liver cancer, solid tumor cancers, leukemia, and skin cancer related to exposure to sunlight. Some women use green tea to fight human papilloma virus (HPV), which can cause genital warts, the growth of abnormal cells in the cervix (cervical dysplasia), and cervical cancer.

Green tea is also taken by mouth for Parkinson's disease, diseases of the heart and blood vessels, diabetes, low blood pressure, chronic fatigue syndrome (CFS), dental cavities (caries), kidney stones, and skin damage.

Instead of drinking green tea, some people apply green tea bags to their skin to soothe sunburn and prevent skin cancer due to sun exposure. Green tea bags are also used to decrease puffiness under the eyes, as a compress for tired eyes or headache, and to stop gums from bleeding after a tooth is pulled. A green tea footbath is used for athlete's foot.

Some people gargle with green tea to prevent colds and flu. Green tea extract is also used in mouthwash to reduce pain after tooth removal. Green tea in candy is used for gum disease.

Green tea is used in an ointment for genital warts.

In food, people drink green tea as a beverage

Is Green Tea effective?

There is some scientific evidence that drinking green tea can improve thinking skills, and might help lower cholesterol and other fats called triglycerides. Green tea consumption might also prevent or delay Parkinson's disease and possibly help to prevent cancer of the bladder, esophagus, and pancreas. But green tea does not seem to help prevent stomach cancer.

There isn't enough information to know if green tea is effective for the other conditions people use it for including: kidney disease, heart disease, kidney stones, tooth decay, and others.

Likely Effective for...

  • Genital warts. A specific green tea extract ointment (Veregen, Bradley Pharmaceuticals; Polyphenon E ointment 15%, MediGene AG) is FDA-approved for treating genital warts. Applying the ointment for 10-16 weeks seems to clear these types of warts in 24% to 60% of patients.
  • High cholesterol. People to consume higher amounts of green tea seem to have lower levels of cholesterol, low-density lipoprotein (LDL or "bad") cholesterol, and triglycerides, as well as higher levels of high-density lipoprotein (HDL or "good") cholesterol. Consuming green tea or taking green tea extract containing 150 to 2500 mg of green tea catechins, an antioxidant found in green tea, daily for up to 24 weeks reduces total cholesterol and low-density lipoprotein (LDL or "bad") cholesterol in people with high levels of blood fats or cholesterol.

Possibly Effective for...

  • Abnormal development of cells of the cervix (cervical dysplasia). Taking green tea by mouth or applying it to the skin seems to reduce cervical dysplasia caused by human papilloma virus (HPV) infection.
  • Clogged arteries (coronary artery disease). Population studies suggest that drinking green tea is linked to a reduced risk of clogged arteries. The link seems to be stronger in men than women.
  • Endometrial cancer. Population studies suggest that drinking green tea is linked to a reduced risk of developing endometrial cancer.
  • High blood pressure. There is some conflicting evidence about the effects of tea on high blood pressure. Population research in Chinese people shows that drinking 120-599 mL of green tea or oolong tea daily is linked to a lower risk of developing high blood pressure. Drinking more than 600 mL daily is linked to an even lower risk. Also, early clinical research suggests that taking green tea extract daily for 3 months or drinking green tea three times per day for 4 weeks reduces blood pressure in people with high blood pressure. Analysis of clinical research shows that green tea can reduce systolic blood pressure (the top number) by up to 3.2 mmHg and diastolic blood pressure (the bottom number) by up to 3.4 mmHg in people with or without high blood pressure. But several smaller studies show that green and black tea have no effect on blood pressure.
  • Low blood pressure. Drinking green tea might help increase blood pressure in elderly people who have low blood pressure after eating.
  • Thick, white patches on the gums (oral leukoplakia). Drinking green tea seems to decrease the size of white patches in people with oral leukoplakia.
  • Osteoporosis. A population study suggests that drinking green tea for 10 years is linked to increased bone mineral density. Also, early research suggests that taking a green tea compound containing 500 mg of catechins, an antioxidant in green tea, twice daily for 24 weeks improves bone strength in post-menopausal women with low bone density.
  • Ovarian cancer. Women who regularly drink tea, including green or black tea, appear to have a lower risk of developing ovarian cancer. But green tea does not seem to prevent ovarian cancer from recurring in people with a history of ovarian cancer.
  • Parkinson's disease. Drinking one to four cups of green tea daily seems to provide the most protection against developing Parkinson's disease.

Insufficient Evidence to Rate Effectiveness for...

  • Acne. Early research suggests that applying a solution containing a certain chemical found in green tea to the skin for 8 weeks reduces acne.
  • Abnormal protein buildup in the organs (Amyloidosis). Early research suggests that drinking green tea (Green Darjeeling, FTGFOP1, Teekampagne Projektwerkstatt GmbH, Berlin, Germany) or taking green tea capsules (Praevent-loges, Dr. Loges + Co. GmbH, Winsen/Luhe, Germany) containing green tea extracts for 12 months protects against an increase in heart mass in people with amyloidosis affecting the heart.
  • Athletic performance. There is conflicting evidence about the effects of green tea on athletic performance. Some early research suggests that taking green tea extract as a beverage does not improve breathing or performance in people undergoing endurance training. However, other early research suggests that taking specific pills (Teavigo, Healthy Origins, Pittsburgh, PA) three times daily with meals for a total dose of seven pills, improves some breathing tests during exercise in healthy adults.
  • Bladder cancer. Some population evidence suggests that drinking green tea is linked to a lower risk of bladder cancer. However, some conflicting research suggests that green tea might not reduce the risk of developing bladder cancer.
  • Breast cancer. Population research suggests that drinking green tea is not linked to a reduced risk of breast cancer in Asian people. However, there is some evidence that it might be linked with a reduced risk of breast cancer development in Asian-Americans. Green tea might have different protective effects in people depending on their genotype. In people with early-stage but not late-stage breast cancer, drinking green tea seems to be linked with a reduced risk of breast cancer recurring.
  • Heart disease. Population studies suggest that drinking three or more cups of green tea daily is linked to a decreased risk of death from heart disease or any cause.
  • Cervical cancer. Research suggests that taking a specific type of green tea extract (Polyphenon E) daily for 4 months does not affect cervical cancer risk in women with HPV infection.
  • Colds and flu. Early research suggests that taking a combination of green tea extract (THEA-FLAN 90S, Ito-en Co, Tokyo, Japan) plus theanine (Suntheanine, Taiyo Kagaku Co, Mie, Japan) daily for 5 months lowers the risk of developing the flu. Other early research suggests that taking a specific combination product containing green tea and other ingredients (ImmuneGuard, Nutraceutical Holdings LLC, Orlando, FL) reduces cold and flu symptoms and the duration of illness. But other early research suggests that gargling with green tea (Kakegawa Tea Merchants Association) at least three times daily for 90 days does not prevent the flu in high school students.
  • Colon and rectal cancer. Most evidence suggests that drinking green tea is not linked with a reduced risk of colon or rectal cancer. However, some research suggests that consuming a high amount is linked to a reduce risk, particularly in women. Also taking green tea extract daily for 12 months seems to reduce the redevelopment of colon and rectal tumors (metachronous adenomas) in people who previously underwent surgery to treat colon and rectal tumors.
  • Depression. Population research suggests that Japanese adults who drink four or more cups of green tea daily have a 44% to 51% lower risk for depression than those who drink one cup or less.
  • Diabetes. Population research suggests that Japanese adults, particularly women, who drink 6 or more cups of green tea daily, have a lower risk of developing diabetes. Also, population research suggests that drinking at least one cup of green tea per week is linked with a lower risk of developing impaired fasting blood sugar in Chinese people. Impaired fasting blood sugar is a risk factor for developing type 2 diabetes. However, some research shows that drinking green tea three times per day does not help control blood sugar in people with prediabetes. Also, taking green tea extract does not seem to help control sugar or insulin levels in people who already have diabetes. Overall, some evidence suggests that drinking green tea might help prevent diabetes from developing. But most research suggests that drinking green tea or taking green tea extract does not help control blood sugar in people who already have diabetes.
  • Esophageal cancer. Some population research suggests that drinking green tea is linked to a reduced risk of esophageal cancer. But there is some conflicting research. Some research suggests that drinking green tea is linked to a reduced risk of esophageal cancer in only women, but not men. Also, some population research suggests that drinking green tea that is very hot is linked to an increased risk of esophageal cancer. Drinking decaffeinated green tea does not seem to benefit people already diagnosed with esophageal cancer.
  • Stomach cancer. There is conflicting evidence about the effects of green tea on stomach cancer risk. Some population research suggests that drinking at least 5 cups of green tea daily is not linked with a reduced risk of stomach cancer. But other population research suggests that drinking at least 10 cups of green tea daily is linked with a reduced risk of stomach cancer.
  • Fertility problems. Early research suggests that taking a specific product containing a mixture of Vitex agnus-castus extract, green tea extract, and L-arginine, as well as some vitamins and minerals (FertilityBlend, The Daily Wellness Company, Mountain View, CA) increases pregnancy rates in women who have trouble conceiving.
  • Allergy to Japanese cedar (pollinosis). Early research suggests that drinking a type of green tea called "Benifuuki" daily for 6-10 weeks before being exposed to Japanese cedar pollen can reduce allergy symptoms, including throat pain, nose blowing, and tears.
  • Leukemia. Population research suggests that Taiwanese people who drink higher amounts of green tea have a lower risk of developing leukemia. Other population research shows that Chinese people who drink at least one cup of green tea for at least 20 years have a lower risk of developing leukemia.
  • Liver cancer. Population research suggests that drinking green tea is not linked to a reduced risk of liver cancer.
  • Lung cancer. There is conflicting evidence about the effects of green tea on lung cancer risk. One population study suggests that drinking at least 5 cups of green tea daily is not linked with a reduced risk of death related to lung cancer. However, men who consume high amounts of phytoestrogens, chemicals found in green tea, have a lower risk of developing lung cancer. Also, some population research suggests that increasing green tea intake by two cups daily or drinking 7-10 cups of green tea daily is linked with a reduced risk of lung cancer.
  • Mental alertness. Green tea contains caffeine. Drinking beverages that contain caffeine seems to help people maintain mental alertness throughout the day. Combining caffeine with sugar as an "energy drink" seems to improve mental performance more than caffeine or sugar alone. However, there is conflicting evidence regarding green tea on mental alertness. Some research shows that taking a combination of green tea extract and L-theanine (LGNC-07, LG Household & Health Care, Ltd, Korea) improves memory and attention in people with mild mental problems. However, taking a single dose of a certain chemical in green tea called epigallocathechin-3-gallate (EGCG) does not seem to improve move or mental performance in healthy adults.
  • Metabolic syndrome. Early research suggests that taking 1000 mg of green tea extract daily or drinking four cups of green tea daily for 8 weeks does not improve blood pressure, cholesterol levels, or blood sugar in obese people with metabolic syndrome.
  • Nonalcoholic fatty liver disease (NAFLD). Research suggests that drinking green tea daily for 12 weeks does not affect body weight or body mass but does reduce body fat percentage and fatty liver disease severity in people with NAFLD.
  • Obesity. There is conflicting evidence about the effects of green tea in obese people. Some early research shows that certain specific green tea extracts (AR25, Exolise, Arkopharma, Carros, France; Sunphenon 90LB, Taiyo Kagaku Ltd, Yokkaichi, Japan; Herbal One Green Tea Extract, Herbal One Co., Ltd., Nakornprathom, Thailand) reduce weight in obese people. Other early research suggests that drinking green tea or green tea-containing beverages can reduce body weight and body mass index (BMI) in obese adults or children. Also, multi-ingredient products containing green tea might increase weight loss in obese or overweight adults. The effect of green tea on weight loss seems to be linked with the amount of catechins or caffeine contained in the beverage or supplement. However, some research suggests that taking green tea extracts or drinking green tea does not reduce body weight or BMI. Overall, research suggests that taking green tea extract along with caffeine seems to slightly reduce BMI, body weight and waist circumference compared to caffeine alone. But, taking green tea extract without caffeine does not seem to reduce weight.
  • Mouth cancer. Population research suggests that drinking green tea is linked with a reduced risk of developing mouth cancer. Also, early research suggests that taking green tea extract three times daily after meals for 12 weeks increases healing responses in people with mouth cancer.
  • Pancreatic cancer. Population research suggests that drinking green tea is linked to a reduced risk of pancreatic cancer.
  • Gum disease (periodontal disease). Chewing candy that contains green tea extract seems to control plaque build-up on the teeth and reduce gum swelling. Also population research suggests that drinking green tea is linked with a reduced risk of gum disease. Also, applying a gel containing green tea extract improves symptoms in people with long-term gum disease.
  • Pneumonia. Population research suggests that Japanese women who drink green tea have a lower risk of death from pneumonia compared to those who don't drink green tea.
  • Pain after surgery. Research suggests that using a mouthwash containing green tea extract twice daily beginning the day after tooth removal surgery reduces pain and the need to use painkillers.
  • Prostate cancer. Some research suggests that men who drink more green tea or who take products containing green tea antioxidants seem to have a lower risk of developing prostate cancer. But conflicting research exists. Green tea or green tea extracts do not seem to slow the progression of prostate cancer that has already been diagnosed.
  • Stress. Early research suggests that taking a specific brand of green tea extract (Teavigo, DSM, Netherlands) by mouth for 7 days reduces stress and increases calmness in healthy people.
  • Stroke. According to one study in Japan, drinking 3 cups of green tea daily seems to be linked with a lower risk of having a stroke compared to drinking one cup or no tea.
  • Athlete's foot. Research suggests that using a footbath containing green tea extract (Sunphenon BG-3,Taiyo Kagaku Co. Ltd., Yokkaichi, Mie, Japan) for 15 minutes once daily for 12 weeks does not improve symptoms of athletes foot, but does improve skin condition.
  • Inflammatory bowel disease (ulcerative colitis). Early research suggests that taking a specific green tea product (Polyphenon E, Mitsui-Norin, Fujieda, Japan) twice daily for 8 weeks might improve inflammatory bowel disease and help people with this condition achieve remission.
  • Upper respiratory tract infection. Early research suggests that gargling and swallowing green tea (Morgentau, Ronnefeld KG, Germany) over 4 days is less effective than labdanum lozenges (CYSTUS052, Dr Pandalis Urheimische Medizin GmbH & Co. KG, Germany) for reducing symptoms of upper respiratory tract infections.
  • Wrinkled skin. Some early research suggests that taking green tea antioxidants twice daily for 2 years does not reduce the signs of sun damage to the face in women. Also, applying a green tea cream and taking green tea by mouth daily seems to improve some aspects of skin aging in women, but overall appearance of skin does not seem to improve. However, some early research shows that drinking a beverage containing green tea antioxidants improves skin roughness, hydration, and elasticity in middle-aged women.
  • Other conditions.
More evidence is needed to rate green tea for these uses.

Natural Medicines Comprehensive Database rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, and Insufficient Evidence to Rate (detailed description of each of the ratings).


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