Green Tea
Green tea (Camellia sinensis): what NIH and Cochrane found for weight, cholesterol and heart health, and why extract capsules have been linked to liver injury and drug interactions.
Content last updated . This page has not been medically reviewed.
Safety first. Natural products can cause side effects and interact with medicines. Read herb safety and interactions before you use anything on this page.
Liver warning first. A cup of green tea and a green tea extract capsule are not the same thing. NIH reports no safety concerns for green tea as a drink in adults, but says liver injury, although uncommon, has been reported mainly with extracts in tablet or capsule form. [1] If you take an extract and notice abdominal pain, dark urine or yellowing of the skin or eyes, stop and contact a clinician. [2] See Liver Safety and Supplements for warning signs.
What it is
Green, black and oolong teas all come from the same plant and differ in how the leaves are processed. For green tea, the leaves are steamed, pan fried and dried but not fermented. [1] The plant is Camellia sinensis (L.) Kuntze, family Theaceae, and the part used is the leaf. [3] This page covers the plant and its extracts as a remedy. The drink itself, including how it compares with black, white and oolong tea, is covered in Green, Black, White and Oolong Tea and What Is Herbal Tea?. Matcha and extract are compared on Green Tea vs Matcha vs Green Tea Extract.Traditional use (not proof)
NIH says the tea plant was first cultivated in China thousands of years ago, and that there is evidence of tea being used for health purposes dating back about 3,000 years. [1] That history describes how people have used the plant. It does not show that tea treats any condition.What research shows (research, not tradition)
NIH says that although many studies exist, definite conclusions cannot yet be reached on most of the purposes for which green tea is used. [1]| Use | What the source found | Evidence label | Form studied |
|---|---|---|---|
| Cancer risk | NIH: the overall results of studies have been inconsistent. [1] | Mixed | Tea and extracts |
| Heart disease | NIH: linked to lower coronary heart disease risk in Asian populations but not in Western populations. [1] | Mixed (observational) | Tea drinking |
| Body weight | NIH: catechins and caffeine may have a modest effect. [1] A Cochrane review of 14 trials found a small, statistically non-significant weight loss that was not likely to be clinically important. [4] | Promising but limited, small effect | Tea and extracts, 12 to 13 week trials |
| Blood cholesterol | NIH: total and LDL cholesterol fell to a small extent in randomized studies, mostly of extract supplements. [1] | Small effect | Mostly extracts |
| Genital warts | The FDA has approved a specific green tea extract ointment as a prescription drug for this. [1] | Established for that product only | Prescription ointment |
The Cochrane review pooled six studies done outside Japan and found almost no difference in weight. Results from eight Japanese studies could not be pooled. [4] For a wider look at weight-loss claims, see Weight-Loss Supplements, Fat Burners, Detox Teas and Vinegar.
Forms and why the form matters
Tea, matcha powder and extract capsules differ in catechin content and in how fast the body absorbs them. The United States Pharmacopeia (USP) panel noted that catechin profiles of extracts vary significantly with manufacturing processes. [2] Cholesterol results come mostly from extract studies, not from tea. [1] A result for one form should not be assumed for another. See Herb Forms and Preparations.Quality
NIH notes that dietary supplements are not approved by the FDA before they are sold. [1] Extract strength differs between products. See Quality Testing and Certifications.Official statements
- NCCIH (US NIH), updated February 2025: conclusions on most uses cannot yet be reached; liver and interaction cautions for extracts. [1]
- US Pharmacopeia expert panel, 2020: cautionary label for green tea extract. [2]
Frequently asked questions
Is green tea extract safe for the liver?
Liver injury is uncommon but has been reported, mainly with extract capsules and tablets. [1] A 2020 USP review recommends a liver caution on extract labels. [2] Anyone with a liver problem should ask a clinician before using one.
Does green tea help with weight loss?
NIH says catechins and caffeine may have a modest effect. [1] A Cochrane review found a small, non-significant weight loss unlikely to matter clinically. [4]
Is drinking green tea risky?
NIH reports no safety concerns for green tea as a beverage in adults, but it contains caffeine. [1]
Does green tea lower cholesterol?
In randomized studies, mostly of extracts, total and LDL cholesterol fell to a small extent. [1]
Can green tea affect my medicines?
Yes, for some. NIH names nadolol and atorvastatin and says there may be others. [1] Ask a pharmacist before using green tea supplements. See Herb Safety and Interactions.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety and who should ask first
- Liver: NIH says people with a specific immune-related gene variant appear especially susceptible, and between 5 and 15 percent of Americans have it. [1] A 2020 USP expert panel review said published case reports link liver injury to intakes of the main catechin (EGCG) from 140 mg to about 1000 mg a day, with large differences between people. [2] A US randomized trial of a high, sustained extract dose found 26 of 513 women (5.1%) had moderate or worse liver test abnormalities, and the liver enzyme ALT returned to normal when the extract was stopped and rose again when restarted. [5] A 2016 review of 34 trials judged serious liver events to be rare, though it called its results not conclusive. [6] Both can be true: harm is uncommon, but it has been documented.
- USP label wording (2020): for powdered decaffeinated green tea extract, USP included a required warning that tells people not to take it on an empty stomach, to take it with food, and not to use it if they have a liver problem. [2]
- Medicines: NIH reports that high doses of green tea reduced blood levels of nadolol, a beta-blocker, and that extract can reduce blood levels of atorvastatin. It adds that green tea may interact with other medicines. [1] See How Interactions Work and ask a pharmacist.
- Other side effects: extract supplements can cause nausea, constipation, abdominal discomfort and increased blood pressure. [1]
- Caffeine, pregnancy and breastfeeding: green tea contains caffeine. NIH says caffeine intake in pregnancy should not exceed moderate levels, and caffeine can pass to an infant through breast milk. [1] See Pregnancy and Breastfeeding.
- Iron: Memorial Sloan Kettering notes that green tea can affect the way iron is absorbed. [7] Ask a clinician if you take iron or have anemia.
- Children, older adults, kidney disease: the sources we read gave no specific guidance. Ask a clinician.
- Before surgery: the sources we read gave no green tea specific advice. Tell the surgical team about every herb and supplement. See Supplements Before Surgery.
References
- National Center for Complementary and Integrative Health (NIH). Green Tea: Usefulness and Safety. Page last updated February 2025. Read 2026-10-23.
- Oketch-Rabah HA, et al. United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts. Toxicology Reports, 2020. Read 2026-10-23.
- GBIF Secretariat. Camellia sinensis (L.) Kuntze, species match. GBIF Backbone Taxonomy. Read 2026-10-23.
- Jurgens TM, et al. Green tea for weight loss and weight maintenance in overweight or obese adults. Cochrane Database of Systematic Reviews, 2012. Read 2026-10-23.
- Yu Z, et al. Effect of green tea supplements on liver enzyme elevation: results from a randomized intervention study in the United States. Cancer Prevention Research, 2017. Read 2026-10-23.
- Isomura T, et al. Liver-related safety assessment of green tea extracts in humans: a systematic review of randomized controlled trials. European Journal of Clinical Nutrition, 2016. Read 2026-10-23.
- Memorial Sloan Kettering Cancer Center. About Herbs: Green Tea. Read 2026-10-23.