Green tea

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What is it?

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). People commonly drink green tea as a beverage.

As a prescription, green tea is used for genital warts. As a drink or supplement, it is sometimes used for high levels of cholesterol or other fats (lipids) in the blood (hyperlipidemia) and high blood pressure, to prevent heart disease, and to prevent cancer of the lining of the uterus (endometrial cancer) and ovarian cancer. It is also used for many other conditions, but there is no good scientific evidence to support these other uses.

It is effective?
Natural Medicines rates effectiveness based on scientific evidence according to the following scale: Effective, Likely Effective, Possibly Effective, Possibly Ineffective, Likely Ineffective, Ineffective, and Insufficient Evidence to Rate.

Probably Effective for …

  • Genital warts. A specific green tea extract ointment (Veregen, Bradley Pharmaceuticals; Polyphenon E ointment 15%, MediGene AG) is available as a prescription product for treating genital warts. Applying the ointment for 10-16 weeks seems to clear these types of warts in 24% to 60% of patients.

Possibly Effective for …

  • Heart 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. Also, people who drink at least three cups of green tea daily might have a lower risk of death from heart disease.
  • Cancer of the lining of the uterus (endometrial cancer). Population studies suggest that drinking green tea is linked to a reduced risk of developing endometrial cancer.
  • High levels of cholesterol or other fats (lipids) in the blood (hyperlipidemia). People who consume higher amounts of green tea seem to have lower levels of total cholesterol, low-density lipoprotein (LDL or “bad”) cholesterol, and blood fats called triglycerides. They also seem to have higher levels of high-density lipoprotein (HDL or “good”) cholesterol. Consuming green tea or taking green tea extract daily for up to 24 weeks may reduce total cholesterol and LDL cholesterol. Early research also suggests that green tea extract might reduce damage to vein and artery walls in people with high cholesterol.
  • High blood pressure. Drinking green tea might reduce the risk of developing high blood pressure. It might also slightly lower blood pressure in people with high blood pressure. But not all research agrees.
  • 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 people who have already had ovarian cancer from getting ovarian cancer again.

Insufficient Evidence to Make a Determination for …

  • Acne. Most early research suggests that applying green tea extract to the skin reduces acne.
  • Decline in memory and thinking skills that occurs normally with age. Most early research suggests that taking green tea does not improve memory or thinking skills in older adults.
  • Abnormal protein buildup in the body (amyloidosis). Early research shows that drinking green tea or taking 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 doesn’t improve breathing or performance in people undergoing endurance training. But other early research shows that taking specific pills containing a component of green tea three times daily with meals for a total dose of seven pills, improves some breathing tests during exercise in healthy adults.
  • A blood disorder that reduces levels of protein in the blood called hemoglobin (beta-thalassemia). Patients with beta-thalassemia might develop high iron levels. Early research suggests that taking an iron chelator medication and drinking green tea after meals helps the body to remove more iron than using the iron chelator alone.
  • Bladder cancer. Some population evidence suggests that drinking green tea is linked to a lower risk of bladder cancer. But some conflicting research exists.
  • Breast cancer. Population research suggests that drinking green tea is not linked to a reduced risk of breast cancer. But there is some evidence that it might be linked with a reduced risk of breast cancer development in Asian-Americans but not Asian people. Green tea might have different protective effects in people depending on their genotype or whether they have gone through menopause. 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.
  • Cancer of the cervix. Research suggests that taking a specific green tea extract daily for 4 months does not affect cervical cancer risk in women with HPV infection.
  • Abnormal cells on the surface of the cervix (cervical dysplasia). Early research shows that taking a green tea product by mouth or applying it to the skin might reduce cervical lesions caused by human papilloma virus (HPV) infection.
  • Memory and thinking skills (cognitive function). Early research shows that taking a chemical found in green tea does not seem to improve cognitive function in healthy adults.
  • Decline in memory and thinking skills in older people that is more than what is normal for their age. Drinking green tea at least once per week might reduce the risk of a decline in memory and thinking skills in older people. Also, early research shows that taking green tea extract might help to improve memory by a small amount in older people with a decline in memory and thinking skills.
  • Non-cancerous growths in the large intestine and rectum (colorectal adenoma). Early research shows that taking green tea extract might reduce the risk for new growths in people who have already had these growths removed.
  • Colon cancer, rectal cancer. Some evidence suggests that drinking green tea is linked with a reduced risk of colon or rectal cancer, particularly in women. But not all research agrees.
  • Common cold. Early research shows that taking a specific product containing green tea and other ingredients reduces cold symptoms and duration.
  • Diseases, such as Alzheimer disease, that interfere with thinking (dementia). Drinking green tea at least once per week might reduce the risk of a decline in memory and thinking skills in older people. This might reduce the risk of dementia.
  • Depression. Population research suggests that Japanese adults who drink four or more cups of green tea daily have a lower risk for depression than those who drink one cup or less.
  • Diabetes. Overall, some evidence suggests that drinking green tea might help prevent diabetes from developing. But in people with diabetes, most research suggests that drinking green tea or taking green tea extract does not help control blood sugar. Taking green tea extract might help to improve body weight and levels of blood fats in people with type 2 diabetes.
  • Dry eye. Early research shows that applying green tea extract into the eyes along with using eye drops helps to reduce eye itching, burning, and redness.
  • Menstrual cramps (dysmenorrhea). Some research shows that drinking green tea might reduce the risk for having menstrual cramps.
  • Cancer of the esophagus. 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.
  • Fractures. Early research found that drinking green tea is linked to a reduced risk of fracture when compared with not drinking green tea.
  • Stomach cancer. 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.
  • Low blood pressure. Early research shows that drinking green tea might help increase blood pressure in elderly people who have low blood pressure after eating. This increase in blood pressure is probably due to the caffeine in green tea.
  • Flu (influenza). Early research suggests that taking green tea extract and theanine lowers the risk of getting the flu. Other early research suggests that taking a specific product containing green tea and other ingredients reduces flu symptoms and duration. Gargling with green tea at least three times daily for 90 days doesn’t seem to prevent the flu in high school students.
  • Allergy to Japanese cedar pollen. 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.
  • Kidney stones. Early research suggests that people who drink green tea might be less likely to have kidney stones.
  • Cancer of the white blood cells (leukemia). Some population research suggests that people who drink higher amounts of green tea have a lower risk of developing leukemia. But not all research agrees.
  • Liver cancer. Some early research suggests that drinking green tea is not linked to a reduced risk of liver cancer. But other early research has found that drinking green tea is linked to a lower risk of liver cancer in women but not men.
  • Lung cancer. Some research has found that drinking at least 5 cups of green tea daily is not linked with a reduced risk of death related to lung cancer. But 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. But taking a single dose of a certain chemical in green tea called epigallocathechin-3-gallate (EGCG) doesn’t seem to improve move or mental performance in healthy adults.
  • A grouping of symptoms that increase the risk of diabetes, heart disease, and stroke (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.
  • Cancer of white blood cells called plasma cells (multiple myeloma). Drinking green tea does not seem to reduce the risk for multiple myeloma.
  • Heart attack. Drinking at least one cup of green tea per day has been linked with a lower risk of heart attack compared to drinking less than one cup per day.
  • Cancer of the upper part of the throat behind the nose (nasopharyngeal cancer). Some research shows that drinking more green tea is linked with a reduced risk of having nasopharyngeal cancer.
  • Build up of fat in the liver in people who drink little or no alcohol (nonalcoholic fatty liver disease or NAFLD). Some research shows that drinking green tea daily for 12 weeks doesn’t reduce body weight or body mass in people with NAFLD. But it might improve fatty liver disease severity. Also taking green tea extract might improve markers of liver injury, body mass, and cholesterol in people with NAFLD.
  • Cancer that starts in white blood cells (non-Hodgkin lymphoma). Some research suggests that drinking at least 3.5 cups of green tea daily is not linked to a reduced risk of developing non-Hodgkin lymphoma.
  • Obesity. The best evidence to date suggests that taking green tea that contains caffeine might slightly reduce body weight in people with obesity. It seems to work better than caffeine alone. But the amount of weight loss is small and probably not meaningful. Also, taking decaffeinated green tea might not help.
  • 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.
  • Weak and brittle bones (osteoporosis). Early research found that drinking green tea for 10 years is linked to increased bone mineral density. Early research also shows that taking green tea extract daily for 24 weeks improves biomarkers of bone density in postmenopausal women with low bone density. But taking green tea extract does not seem to improve bone density in postmenopausal women when measured using bone density scanning.
  • Death from any cause. Some research suggests that drinking more green tea daily is linked to a reduced risk of death from any cause.
  • Pancreatic cancer. Although some research disagrees, most research suggests that drinking green tea is not linked to a reduced risk of pancreatic cancer.
  • Parkinson disease. Some research shows that drinking caffeinated beverages can reduce the risk of Parkinson disease. Drinking one to four cups daily seems to provide the most protection against developing Parkinson disease.
  • A serious gum infection (periodontitis). 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 shows that taking products containing green tea antioxidants reduces the risk of prostate cancer in high-risk patients. Also, drinking more green tea is associated with a reduced risk of having prostate cancer. But taking green tea or green tea extracts does not seem to slow the progression of prostate cancer that has already been diagnosed.
  • Diarrhea caused by radiation therapy. Early research shows that taking a green tea tablet during pelvic radiation treatment might reduce how often someone has diarrhea.
  • Nausea and vomiting caused by radiation therapy. Early research shows that taking a green tea tablet during pelvic radiation treatment might not reduce how often someone vomits.
  • Stress. Early research suggests that taking green tea extract by mouth for 7 days reduces stress and increases calmness in healthy people.
  • Stroke. Population research suggests that drinking more green tea daily is linked to a reduced risk of having a stroke.
  • An autoimmune disease that causes widespread swelling (systemic lupus erythematosus or SLE). Early research shows that green tea extract seems to improve symptoms and general health in people with lupus.
  • Athlete’s foot (Tinea pedis). Research suggests that using a footbath containing green tea extract for 15 minutes once daily for 12 weeks doesn’t improve symptoms of athlete’s foot, but does improve skin condition.
  • A type of inflammatory bowel disease (ulcerative colitis). Early research suggests that taking a specific green tea product twice daily for 8 weeks might improve inflammatory bowel disease and help people with this condition achieve remission.
  • Upper airway infection. Early research suggests that gargling and swallowing green tea over 4 days is less effective than labdanum lozenges for reducing symptoms of upper respiratory tract infections.
  • Infections of the kidney, bladder, or urethra (urinary tract infections or UTIs). A small study shows that adding green tea capsules to antibiotic treatment seems to reduce symptoms of UTI more than taking the antibiotic alone.
  • Skin wrinkles from sun damage. 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.
  • Anxiety.
  • Chronic fatigue syndrome.
  • A type of inflammatory bowel disease (Crohn disease).
  • Headache.
  • Inability to become pregnant within a year of trying to conceive (infertility).
  • Skin cancer.
  • White patches inside the mouth that are usually caused by smoking (oral leukoplakia).
  • Other conditions.

More evidence is needed to rate green tea for these uses.

How does it work?
The useful parts of green tea are the leaf bud, leaf, and stem. Green tea is not fermented and is produced by steaming fresh leaves at high temperatures. During this process, it is able to maintain important molecules called polyphenols, which seem to be responsible for many of the benefits of green tea.

Polyphenols might be able to prevent inflammation and swelling, protect cartilage between the bones, and lessen joint degeneration. They also seem to be able to fight human papilloma virus (HPV) infections and reduce the growth of abnormal cells in the cervix (cervical dysplasia). Research cannot yet explain how this works.

Green tea contains 2% to 4% caffeine, which affects thinking and alertness, increases urine output, and may improve the function of brain messengers important in Parkinson’s disease. Caffeine is thought to stimulate the nervous system, heart, and muscles by increasing the release of certain chemicals in the brain called “neurotransmitters.”

Antioxidants and other substances in green tea might help protect the heart and blood vessels.

Is there concern for the safety of its use?
When taken by mouth: Drinking green tea is LIKELY SAFE for most healthy adults when consumed in moderate amounts (about 8 cups per day).

Green tea extract is POSSIBLY SAFE for most people when taken by mouth for up to 2 years or when used as a mouthwash, short-term. In some people, green tea extract can cause stomach upset and constipation. Green tea extracts have been reported to cause liver and kidney problems in rare cases.

Drinking green tea is POSSIBLY UNSAFE when consumed for a long time or in high doses (more than 8 cups per day). Drinking large amounts of green tea might cause side effects due to the caffeine content. 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 also contains a chemical that has been linked with liver injury when used in high doses. In order to reduce the risk for liver injury, take green tea extract with food.

When applied to the skin: Green tea extract is LIKELY SAFE when a specific, FDA-approved ointment (Veregen, Bradley Pharmaceuticals) is applied to the skin, short-term. Green tea is POSSIBLY SAFE when other green tea products are applied to the skin, short-term.

Special Precautions & Warnings:

Children: Green tea is POSSIBLY SAFE for children when taken by mouth in amounts commonly found in foods and beverages, or when used for gargling three times daily for up to 90 days. Not enough is known about safety of green tea extract when taken by mouth in children. However, cases of liver damage have been reported for adults who used green tea extract. Therefore, some experts recommend that children under the age of 18 years old do not take green tea extract.

Pregnancy and breast-feeding: If you are pregnant or breast-feeding, drinking green tea is POSSIBLY SAFE in amounts of 6 cups per day or less. This amount of green tea provides about 300 mg of caffeine. Drinking more than this amount during pregnancy is POSSIBLY UNSAFE and has been linked to an increased risk of miscarriage and other negative effects. Also, green tea might increase the risk of birth defects associated with folic acid deficiency.

In women who are nursing, caffeine passes into breast milk and can affect a nursing infant. Nursing mothers should closely monitor caffeine intake to make sure it is on the low side (2-3 cups per day). High intake of caffeine by nursing mothers can cause sleep problems, irritability, and increased bowel activity in breast-fed infants.

“Tired blood” (anemia): Drinking green tea may make anemia worse.

Anxiety disorders: The caffeine in green tea might make anxiety worse.

Bleeding disorders: Caffeine in green tea might increase the risk of bleeding. Don’t drink green tea if you have a bleeding disorder.

Heart conditions: Caffeine in green tea might cause irregular heartbeat.

Diabetes: Caffeine in green tea might affect blood sugar control. If you drink green tea and have diabetes, monitor your blood sugar carefully.

Diarrhea: Green tea contains caffeine. The caffeine in green tea, especially when taken in large amounts, can worsen diarrhea.

Seizures: Green tea contains caffeine. There is a concern that high doses of caffeine might cause seizures or decrease the effects of drugs used to prevent seizures. If you have ever had a seizure, don’t use high doses of caffeine or caffeine-containing supplements such as green tea.

Glaucoma: Drinking green tea increases pressure inside the eye. The increase occurs within 30 minutes and lasts for at least 90 minutes.

High blood pressure: The caffeine in green tea might increase blood pressure in people with high blood pressure. However, this effect might be less in people who consume caffeine from green tea or other sources regularly.

Irritable bowel syndrome (IBS): Green tea contains caffeine. The caffeine in green tea, especially when taken in large amounts, might worsen the diarrhea some people have with IBS.

Liver disease: Green tea extract supplements have been linked to rare cases of liver damage. Green tea extracts might make liver disease worse. Talk to your doctor before taking a green tea extract. Tell your doctor if you have signs of liver damage such as yellowing skin, dark urine, or abdominal pain. Keep in mind that drinking green tea as a beverage in normal amounts is still probably safe.

Weak bones (osteoporosis): Drinking green tea can increase the amount of calcium that is flushed out in the urine. This might weaken bones. If you have osteoporosis, don’t drink more than 6 cups of green tea per day. Taking calcium supplements may help make up for calcium that is lost. If you are generally healthy and getting enough calcium from your food or supplements, taking up to 400 mg of caffeine (about 8 cups of green tea) per day doesn’t seem to increase the risk of getting osteoporosis.

Are there any drug interactions?

Adenosine (Adenocard)

Interaction Rating=Moderate Be cautious with this combination.

Green tea contains caffeine. The caffeine in green tea might block the affects of adenosine (Adenocard). Adenosine (Adenocard) is often used by doctors to do a test on the heart. This test is called a cardiac stress test. Stop consuming green tea or other caffeine-containing products at least 24 hours before a cardiac stress test.

Alcohol

Interaction Rating=Minor Be watchful with this combination.

The body breaks down the caffeine in green tea to get rid of it. Alcohol can decrease how quickly the body breaks down caffeine. Taking green tea along with alcohol might cause too much caffeine in the bloodstream and caffeine side effects including jitteriness, headache, and fast heartbeat.

Amphetamines

Interaction Rating=Major Do not take this combination.

Stimulant drugs such as amphetamines speed up the nervous system. By speeding up the nervous system, stimulant medications can make you feel jittery and increase your heart rate. The caffeine in green tea might also speed up the nervous system. Taking green tea along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure. Avoid taking stimulant drugs along with caffeine.

Antibiotics (Quinolone antibiotics)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down caffeine to get rid of it. Some antibiotics might decrease how quickly the body breaks down caffeine. Taking these antibiotics along with green tea can increase the risk of side effects including jitteriness, headache, increased heart rate, and other side effects.
Some antibiotics that decrease how quickly the body breaks down caffeine include ciprofloxacin (Cipro), enoxacin (Penetrex), norfloxacin (Chibroxin, Noroxin), sparfloxacin (Zagam), trovafloxacin (Trovan), and grepafloxacin (Raxar).

Birth control pills (Contraceptive drugs)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down the caffeine in green tea to get rid of it. Birth control pills can decrease how quickly the body breaks down caffeine. Taking green tea along with birth control pills can cause jitteriness, headache, fast heartbeat, and other side effects.
Some birth control pills include ethinyl estradiol and levonorgestrel (Triphasil), ethinyl estradiol and norethindrone (Ortho-Novum 1/35, Ortho-Novum 7/7/7), and others.

Cimetidine (Tagamet)

Interaction Rating=Moderate Be cautious with this combination.

Green tea contains caffeine. The body breaks down caffeine to get rid of it. Cimetidine (Tagamet) can decrease how quickly your body breaks down caffeine. Taking cimetidine (Tagamet) along with green tea might increase the chance of caffeine side effects including jitteriness, headache, fast heartbeat, and others.

Clozapine (Clozaril)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down clozapine (Clozaril) to get rid of it. The caffeine in green tea seems to decrease how quickly the body breaks down clozapine (Clozaril). Taking green tea along with clozapine (Clozaril) can increase the effects and side effects of clozapine (Clozaril).

Dipyridamole (Persantine)

Interaction Rating=Moderate Be cautious with this combination.

Green tea contains caffeine. The caffeine in green tea might block the affects of dipyridamole (Persantine). Dipyridamole (Persantine) is often used by doctors to do a test on the heart. This test is called a cardiac stress test. Stop drinking green tea or other caffeine-containing products at least 24 hours before a cardiac stress test.

Disulfiram (Antabuse)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down caffeine to get rid of it. Disulfiram (Antabuse) can decrease how quickly the body gets rid of caffeine. Taking green tea (which contains caffeine) along with disulfiram (Antabuse) might increase the effects and side effects of caffeine including jitteriness, hyperactivity, irritability, and others.

Ephedrine

Interaction Rating=Major Do not take this combination.

Stimulant drugs speed up the nervous system. Caffeine (contained in green tea) and ephedrine are both stimulant drugs. Taking green tea along with ephedrine might cause too much stimulation and sometimes serious side effects and heart problems. Do not take caffeine-containing products and ephedrine at the same time.

Estrogens

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down the caffeine in green tea to get rid of it. Estrogens can decrease how quickly the body breaks down caffeine. Taking estrogen pills and drinking green tea can cause jitteriness, headache, fast heartbeat, and other side effects. If you take estrogen pills limit your caffeine intake.
Some estrogen pills include conjugated equine estrogens (Premarin), ethinyl estradiol, estradiol, and others.

Fluconazole (Diflucan)

Interaction Rating=Minor Be watchful with this combination.

Green tea contains caffeine. The body breaks down caffeine to get rid of it. Fluconazole (Diflucan) might decrease how quickly the body gets rid of caffeine and cause caffeine to stay in the body too long. Taking fluconazole (Diflucan) along with green tea might increase the risk of side effects such as nervousness, anxiety, and insomnia.

Fluvoxamine (Luvox)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down the caffeine in green tea to get rid of it. Fluvoxamine (Luvox) can decrease how quickly the body breaks down caffeine. Taking green tea along with fluvoxamine (Luvox) might cause too much caffeine in the body, and increase the effects and side effects of caffeine.

Lithium

Interaction Rating=Moderate Be cautious with this combination.

Your body naturally gets rid of lithium. The caffeine in green tea can increase how quickly your body gets rid of lithium. If you take products that contain caffeine and you take lithium, stop taking caffeine products slowly. Stopping caffeine too quickly can increase the side effects of lithium.

Medications for depression (MAOIs)

Interaction Rating=Moderate Be cautious with this combination.

The caffeine in green tea can stimulate the body. Some medications used for depression can also stimulate the body. Drinking green tea and taking some medications for depression might cause too much stimulation of the body and serious side effects including fast heartbeat, high blood pressure, nervousness, and others.
Some of these medications used for depression include phenelzine (Nardil), tranylcypromine (Parnate), and others.

Medications for diabetes (Antidiabetes drugs)

Interaction Rating=Minor Be watchful with this combination.

Green tea contains caffeine. Caffeine might increase blood sugar. Diabetes medications are used to lower blood sugar. Taking some medications for diabetes along with caffeine might decrease the effectiveness of diabetes medications. Monitor your blood sugar closely. The dose of your diabetes medication might need to be changed.
Some medications used for diabetes include glimepiride (Amaryl), glyburide (DiaBeta, Glynase PresTab, Micronase), insulin, pioglitazone (Actos), rosiglitazone (Avandia), chlorpropamide (Diabinese), glipizide (Glucotrol), tolbutamide (Orinase), and others.

Medications that can harm the liver (Hepatotoxic drugs)

Interaction Rating=Moderate Be cautious with this combination.

Green tea extracts might harm the liver. Taking green tea extracts along with medication that might also harm the liver can increase the risk of liver damage. Do not take green tea extracts if you are taking a medication that can harm the liver.
Some medications that can harm the liver include acetaminophen (Tylenol and others), amiodarone (Cordarone), carbamazepine (Tegretol), isoniazid (INH), methotrexate (Rheumatrex), methyldopa (Aldomet), fluconazole (Diflucan), itraconazole (Sporanox), erythromycin (Erythrocin, Ilosone, others), phenytoin (Dilantin) , lovastatin (Mevacor), pravastatin (Pravachol), simvastatin (Zocor), and many others.

Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs)

Interaction Rating=Moderate Be cautious with this combination.

Green tea might slow blood clotting. Taking green tea along with medications that also slow clotting might increase the chances of bruising and bleeding.
Some medications that slow blood clotting include aspirin, clopidogrel (Plavix), diclofenac (Voltaren, Cataflam, others), ibuprofen (Advil, Motrin, others), naproxen (Anaprox, Naprosyn, others), dalteparin (Fragmin), enoxaparin (Lovenox), heparin, warfarin (Coumadin), and others.

Mexiletine (Mexitil)

Interaction Rating=Minor Be watchful with this combination.

Green tea contains caffeine. The body breaks down caffeine to get rid of it. Mexiletine (Mexitil) can decrease how quickly the body breaks down caffeine. Taking Mexiletine (Mexitil) along with green tea might increase the caffeine effects and side effects of green tea.

Nicotine

Interaction Rating=Moderate Be cautious with this combination.

Stimulant drugs such as nicotine speed up the nervous system. By speeding up the nervous system, stimulant medications can make you feel jittery and increase your heart rate. The caffeine in green tea might also speed up the nervous system. Taking green tea along with stimulant drugs might cause serious problems including increased heart rate and high blood pressure. Avoid taking stimulant drugs along with caffeine.

Pentobarbital (Nembutal)

Interaction Rating=Moderate Be cautious with this combination.

The stimulant effects of the caffeine in green tea can block the sleep-producing effects of pentobarbital.

Phenylpropanolamine

Interaction Rating=Moderate Be cautious with this combination.

Green tea contains caffeine. Caffeine can stimulate the body. Phenylpropanolamine can also stimulate the body. Taking green tea and phenylpropanolamine together might cause too much stimulation and increase heartbeat, blood pressure and cause nervousness.

Riluzole (Rilutek)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down riluzole (Rilutek) to get rid of it. Drinking green tea can decrease how quickly the body breaks down riluzole (Rilutek) and increase the effects and side effects of riluzole.

Terbinafine (Lamisil)

Interaction Rating=Minor Be watchful with this combination.

The body breaks down the caffeine in green tea to get rid of it. Terbinafine (Lamisil) can decrease how fast the body gets rid of caffeine. Taking green tea along with terbinafine (Lamisil) can increase the risk of caffeine side effects including jitteriness, headache, increased heartbeat, and other effects.

Theophylline

Interaction Rating=Moderate Be cautious with this combination.

Green tea contains caffeine. Caffeine works similarly to theophylline. Caffeine can also decrease how quickly the body gets rid of theophylline. Taking green tea along with theophylline might increase the effects and side effects of theophylline.

Verapamil (Calan, Covera, Isoptin, Verelan)

Interaction Rating=Moderate Be cautious with this combination.

The body breaks down the caffeine in green tea to get rid of it. Verapamil (Calan, Covera, Isoptin, Verelan) can decrease how quickly the body gets rid of caffeine. Drinking green tea and taking verapamil (Calan, Covera, Isoptin, Verelan) can increase the risk of side effects for caffeine including jitteriness, headache, and an increased heartbeat.

Warfarin (Coumadin)

Interaction Rating=Moderate Be cautious with this combination.

Warfarin (Coumadin) is used to slow blood clotting. Large amounts of green tea have been reported to decrease the effectiveness of warfarin (Coumadin). Decreasing the effectiveness of warfarin (Coumadin) might increase the risk of clotting. It is unclear why this interaction might occur. Be sure to have your blood checked regularly. The dose of your warfarin (Coumadin) might need to be changed.

Are there any interactions with herbs and supplements?
Bitter orange: Bitter orange, used along with caffeine or caffeine-containing herbs such as green tea, can increase blood pressure and heart rate in otherwise healthy people. This might damage the heart and blood vessels.
Caffeine-containing herbs and supplements: Green tea contains caffeine. Using green tea along with other herbs and supplements that contain caffeine might increase the effects of caffeine, and also its unwanted side effects. Some natural products that contain caffeine include coffee, black tea, oolong tea, guarana, mate, cola, and others.
Calcium: Green tea contains caffeine. High doses of caffeine can lead to loss of too much calcium in the urine.
Creatine: There is some concern that combining caffeine, ephedra, and creatine might increase the risk of serious unwanted side effects. One athlete who used this combination, as well as some other supplements to improve his performance, suffered a stroke. Researchers worry the stroke might have been caused by the supplements.
Echinacea: Green tea contains caffeine. The body breaks down caffeine to get rid of it. Echinacea can decrease how quickly the body gets rid of caffeine. Drinking green tea and taking echinacea might increase the risk of side effects of caffeine, including jitteriness, headache, and an increased heartbeat.
Ephedra (Ma Huang): Don’t take green tea with ephedra. The caffeine in green tea might increase the effects of ephedra. Using ephedra with caffeine might increase the risk of serious life-threatening or disabling conditions such as hypertension, heart attack, stroke, seizures, and death.
Folic acid: There is some concern that green tea might decrease the activity of folic acid, leaving the body with less than the amount of folic acid it needs.
Genistein-containing herbs and supplements: Green tea contains a chemical called EGCG. Taking EGCG along with the chemical genistein might increase the risk for developing tumors in the intestines. In theory, taking green tea with supplements that contain genistein might increase the risk for tumors. Supplements that contain genistein include soy, kudzu, red clover, alfalfa, broccoli, cauliflower, and others.
Herbs and supplements that might harm the liver: In several cases, people who took green tea developed liver damage. Researchers worry that the damage might have been linked to the green tea. Taking green tea extracts with other herbs or supplements that might harm the liver could increase the risk of harm to the liver. Other products that might adversely affect the liver include bishop’s weed, borage, chaparral, uva ursi, and others.
Herbs and supplements that might slow blood clotting: Green tea contains caffeine. Caffeine may slow blood clotting. Using green tea along with other herbs and supplements that might also slow blood clotting could increase the risk of bleeding in some people. Some of these herbs include angelica, clove, danshen, garlic, ginger, ginkgo, Panax ginseng, and others.
Iron: Green tea might reduce the absorption of iron supplements. For most people, this effect will not be enough to make a difference in their health. But people who don’t have enough iron in their system would be wise to drink green tea between meals rather than with meals to lessen this interaction.
Kudzu: Green tea contains caffeine. The body breaks down caffeine to get rid of it. Kudzu can decrease how quickly the body gets rid of caffeine. Drinking green tea and taking kudzu might increase the risk of side effects of caffeine, including jitteriness, headache, and an increased heartbeat.
Magnesium: Green tea contains caffeine. Caffeine can increase how quickly the body releases magnesium in the urine.
Melatonin: Green tea contains caffeine. Taking caffeine and melatonin together can increase melatonin levels. Caffeine can also increase natural melatonin levels in healthy individuals.

Are there any interactions with food?
Iron: Green tea appears to reduce absorption of iron from foods.
Milk: Adding milk to tea seems to reduce some of tea’s benefits for the heart and blood vessels. Milk might bind and prevent absorption of the antioxidants in tea. But this is controversial. More research is needed to find out how important this interaction really is.
Soy: Soy is high in protein. Taking soy protein along with green tea reduces how much chemicals called catechins the body absorbs from green tea. Taking soy protein while drinking green tea may reduce the effects of green tea. Separate dosing of green tea and soy protein by at least 3 hours to avoid this interaction.

What dose is used?
The following doses have been studied in scientific research:

BY MOUTH:

  • For high levels of cholesterol or other fats (lipids) in the blood (hyperlipidemia): Green tea or green tea extracts containing 150 to 2500 mg catechins, taken in single or 2 divided doses daily for up to 24 weeks, has been used.
  • For high blood pressure: A green tea drink, made by boiling a 3 gram tea bag with 150 mL water, has been used three times daily about 2 hours after each meal for 4 weeks. Also, 379 mg of a specific product containing green tea extract (Olimp Labs, Debica, Poland), taken daily with the morning meal for 3 months, has been used.

APPLIED TO THE SKIN:

  • For genital warts: A specific green tea extract ointment (Veregen, Bradley Pharmaceuticals; Polyphenon E ointment 15%, MediGene AG) applied three times daily to warts for up to 16 weeks, has been used. This product is FDA-approved for treating this condition.

By what other names is the product known?
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, Matcha Green Tea, 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.

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