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Green tea is made from the Camellia sinensis plant. Its dried leaves and leaf buds are used to make several different teas, including black and oolong teas.

Green tea is prepared by steaming and pan-frying the Camellia sinensis leaves and then drying them. Green tea is not fermented, so it's able to maintain important molecules called polyphenols, which seem to be responsible for many of its benefits. It also contains caffeine.

People commonly use a US FDA-approved prescription product containing green tea for genital warts. As a drink or supplement, green tea is sometimes used for high cholesterol, high blood pressure, to prevent heart disease, and to prevent ovarian cancer. It is also used for many other conditions, but there is no good scientific evidence to support most of these uses.

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.
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  • Genital warts.  A specific green tea extract ointment (Polyphenon E ointment 15%) is approved by the US Food and Drug Administration (FDA) for treating external genital warts.
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When taken by mouth: Green tea is commonly consumed as a beverage. Drinking green tea in moderate amounts (about 8 cups daily) is likely safe for most people. Green tea extract is possibly safe when taken for up to 2 years or when used as a mouthwash, short-term.

Drinking more than 8 cups of green tea daily is possibly unsafe. Drinking large amounts might cause side effects due to the caffeine content. These side effects can range from mild to serious and include headache and irregular heartbeat. Green tea extract also contains a chemical that has been linked with liver injury when used in high doses.

When applied to the skin: Green tea extract is likely safe when an FDA-approved ointment is used, short-term. Other green tea products are possibly safe when used appropriately.

Special Precautions & Warnings:

Pregnancy: 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.

Breast-feeding: Caffeine passes into breast milk and can affect a nursing infant. Closely monitor caffeine intake to make sure it is on the low side (2-3 cups per day) while breast-feeding. High intake of caffeine while breast-feeding can cause sleep problems, irritability, and increased bowel activity in breast-fed infants.

Children: Green tea is possibly safe for children when taken by mouth in amounts commonly found in foods and beverages, or when gargled three times daily for up to 90 days. There isn't enough reliable information to know if green tea extract is safe when taken by mouth in children. There's some concern that it might cause liver damage.

Anemia: Drinking green tea may make anemia worse.

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

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

Heart conditions: When taken in large amounts, the caffeine in green tea might cause irregular heartbeat.

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

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

Seizures: Green tea contains caffeine. 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 products 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. But 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 diarrhea in some people 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 green tea extract. Drinking green tea 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 daily. If you are generally healthy and get enough calcium from your food or supplements, drinking about 8 cups of green tea daily doesn't seem to increase the risk of getting osteoporosis.

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.

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. Taking it along with other supplements that contain caffeine might increase caffeine side effects. Examples of supplements that contain caffeine include black tea, coffee, guarana, and yerba mate.
Calcium: Green tea contains caffeine. High doses of caffeine can increase the loss of calcium in the urine.
Creatine: 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. 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: Don't take green tea with 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: Green tea might decrease the activity of folic acid, leaving the body with less folic acid than 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. Taking green tea with supplements that contain genistein might increase the risk for tumors. Examples of supplements that contain genistein include cumin, dyer's broom, kudzu, red clover, and soy.
Herbs and supplements that might harm the liver: Green tea extract might harm the liver. Taking it with other supplements that can also harm the liver might increase the risk of liver damage. Examples of supplements with this effect include garcinia, greater celandine, kava, and kratom.
Herbs and supplements that might slow blood clotting: Green tea contains caffeine. Caffeine might slow blood clotting and increase the risk of bleeding. Taking it with other supplements with similar effects might increase the risk of bleeding in some people. Examples of supplements with this effect include garlic, ginger, ginkgo, nattokinase, and Panax ginseng.
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 should drink green tea between meals rather than with meals to avoid this interaction.
Kudzu: Green tea contains caffeine. 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.

There are no known interactions with foods.

Green tea is commonly consumed as a beverage. Green tea is also available in an FDA-approved ointment.

As a supplement, green tea powder and extracts have most often been used. Green tea products are typically standardized to the amount of polyphenols or antioxidants they provide. Green tea beverages typically contain 178-823 mg of specific polyphenols called catechins per cup. Green tea also contains caffeine. Speak with a healthcare provider to find out what type of product and dose might be best for a specific condition.

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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