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Green tea benefits are some of the most studied in nutrition research, yet the findings are less clear-cut than the marketing suggests. Green tea comes from the leaves of Camellia sinensis, the same plant as black and oolong tea, and it supplies plant compounds called catechins along with a modest amount of caffeine. Large Japanese studies link regular green tea drinking with lower death rates from heart disease, and small trials show modest drops in cholesterol, but the National Center for Complementary and Integrative Health (NCCIH) says definite conclusions cannot yet be reached for most uses. Here is what green tea is, what the research shows, its side effects and how the brewed drink differs from concentrated supplements.
Peptide Labs sells a few supplements that list green tea leaf extract on the label, described below with their label facts, but no loose or bagged tea. This article is general information, not medical advice.
Key Takeaways
- Green, black and oolong tea all come from Camellia sinensis; green tea leaves are heated and dried but not fermented.
- NCCIH reports no safety concerns for green tea consumed as a beverage by adults, though it does contain caffeine.
- Observational studies in Asian populations link green tea with lower heart disease risk; Western studies have not shown the same.
- A 2020 Cochrane review found inconsistent, limited evidence on green tea and cancer risk.
- Rare liver injury has been reported mainly with concentrated extracts in capsules or tablets, not with brewed tea.
What is green tea?
All true teas come from one plant. According to NCCIH, green tea is made by steaming or pan frying the leaves and then drying them without fermentation, while black tea is fully fermented and oolong is partly fermented. That gentle processing keeps more of the leaf’s catechins intact. The four main catechins are EC, ECG, EGC and EGCG, and EGCG is the most abundant. The tea plant was first cultivated in China thousands of years ago, and NCCIH notes evidence of tea used for health purposes dating back about 3,000 years.
Besides catechins, green tea contains caffeine and the amino acid theanine, which is sold on its own as L-theanine. Matcha is a powdered form made from shade-grown leaves; because the whole leaf is consumed, reviews describe it as the most concentrated source of tea catechins. Green tea is also the base of many supplements, which concentrate those compounds far beyond what a cup provides. That difference matters for safety, as explained below.
Green tea benefits: what the research shows
Thousands of studies have looked at the benefits of green tea, but most are observational, meaning they compare people who drink more tea with people who drink less. Those studies can show associations, not cause and effect, because tea drinkers may differ in diet, smoking or other habits. Randomized trials are fewer, shorter and often test extracts rather than the beverage. The table summarizes the strongest evidence we found.
| Area studied | What the research found | Evidence quality |
|---|---|---|
| Heart disease risk | Lower coronary heart disease risk with green tea in Asian, not Western, populations | Observational; cannot prove cause |
| Cholesterol | Small drops in total and LDL cholesterol; no change in HDL or triglycerides | Randomized trials, mostly of extracts |
| Blood pressure | Cochrane 2013: small reductions in a few trials, results not stable | Few small trials, no heart events measured |
| Cancer | Cochrane 2020: inconsistent results and no link with cancer deaths | Low certainty |
| Body weight | Catechins and caffeine may have a modest effect | Mixed; depends on product and activity |
Heart health
The most widely cited study is the Ohsaki cohort, published in JAMA in 2006. Researchers followed 40,530 Japanese adults aged 40 to 79 for up to 11 years. People who drank more green tea had lower death rates from all causes and from cardiovascular disease, the link was stronger in women, and the strongest association was with stroke deaths. Green tea was not associated with lower cancer deaths. Because this was an observational study in a population where green tea is a daily habit, it cannot show that tea itself caused the difference.
Randomized trials have looked at risk factors rather than heart attacks. A 2013 Cochrane review found 11 trials with 821 participants, seven of them testing green tea. Green tea lowered total and LDL cholesterol and blood pressure, but only a few small studies contributed to each result, the results were not stable when weaker studies were removed, and no trial measured heart events. NCCIH reaches a similar view: small cholesterol reductions, mostly in studies of extracts.
Cancer research
A 2020 Cochrane review pooled 142 studies, including 11 randomized trials of green tea extract and observational data on more than 1.1 million people. The authors found inconsistent results and only limited evidence that green tea lowers overall or site-specific cancer risk, and no association with cancer deaths. Most of the studies were in Asian populations with high green tea intake, which limits how well the findings apply elsewhere. Green tea is not a substitute for screening or for care from an oncology team.
Weight and metabolism
NCCIH says the catechins and caffeine in green tea and its extracts may have a modest effect on body weight, and that results vary with the product and a person’s activity level. Unsweetened tea is a near zero-calorie drink, which can help if it replaces sugary drinks, but it is not a fat burner. Our guides on whether fat burners work and how to boost metabolism cover what actually changes energy balance.
Caffeine and theanine in green tea
In FDA’s caffeine table, a typical serving of green tea lists less caffeine than the same amount of black tea or regular brewed coffee, though the amount varies with the leaf, water temperature and steeping time. Sensitivity to caffeine also varies widely. FDA lists a fast heart rate, insomnia, anxiety, jitters, upset stomach and headache as signs you may have had too much. Our guide on how much caffeine is too much explains FDA’s reference amount and how tea, coffee and energy drinks add up.
If you are pregnant, trying to become pregnant or breastfeeding, talk with your clinician about caffeine from all sources. NCCIH notes that caffeine passes into breast milk. Decaffeinated green tea is an option for people who want the taste with less caffeine.
Green tea side effects and medicine interactions
For most adults, green tea side effects as a beverage come down to caffeine. NCCIH reports no safety concerns for green tea consumed as a drink by adults. Concentrated products are a different story, and several medicines interact with tea.
- Nadolol: NCCIH says large amounts of green tea have been shown to lower blood levels, and so the effectiveness, of nadolol, a beta-blocker used for blood pressure and heart problems.
- Atorvastatin and raloxifene: green tea extract can reduce blood levels of the cholesterol drug atorvastatin, and an NCCIH-funded study found an interaction between green tea and raloxifene, an osteoporosis drug.
- Extract side effects: nausea, constipation, abdominal discomfort and increased blood pressure have been reported with green tea extract supplements.
- Liver: liver injury is uncommon but has been reported, mainly with extracts in tablets or capsules. People with a specific immune-system gene variant, carried by 5 to 15 percent of Americans, appear especially susceptible.
- Other medicines: green tea may interact with other drugs too, so tell your pharmacist about any tea habit or tea-based supplement.
Stop any green tea supplement and contact a clinician promptly if you notice signs of liver trouble, such as yellowing of the skin or eyes, dark urine, unusual tiredness or pain in the upper right abdomen. Our guide to green tea extract covers the liver reports and label warnings for concentrated products in more detail.
Brewed green tea vs supplements made from it
A cup of tea and a capsule of extract are not interchangeable. Extracts are standardized to deliver concentrated catechins, they are often combined with other active ingredients, and they are the products most often linked with liver injury. Brewed tea delivers smaller amounts along with water and a predictable caffeine signal you can taste. FDA has approved one prescription ointment made from a specific green tea extract for a skin condition, but no green tea supplement is approved to diagnose or manage any disease.
Two products we carry list green tea leaf extract as an active ingredient. The ColonBroom GLP-1 Premium Booster capsules combine green tea leaf extract standardized to catechins with green coffee bean, lemon bioflavonoid and cinnamon bark extracts; the label does not state a caffeine amount, and the brand describes its green tea as decaffeinated catechins. The Physician’s CHOICE Probiotics for Weight Management include a Greenselect Phytosome green tea leaf extract in a blend with apple cider vinegar and cayenne extracts, alongside six probiotic strains, prebiotic fiber and enzymes; the brand describes that extract as caffeine free. Both labels advise checking with a doctor if you are pregnant, nursing or taking medication. We list them for label transparency, not as a way to get the benefits of drinking tea.
Whatever form you choose, read the full Supplement Facts panel, look for independent testing (see our guide to third-party tested supplements) and avoid stacking several caffeine-containing products. If you are curious about other traditional ingredients sold as supplements, our cordyceps guide shows how a fungus long used in Chinese medicine holds up in trials.
Frequently Asked Questions
What are the main green tea benefits?
Japanese observational studies link green tea drinking with lower heart disease deaths, and small trials show modest drops in cholesterol. NCCIH says definite conclusions cannot yet be reached for most uses.
Is green tea good for you?
For most adults, green tea as a beverage is a reasonable low-calorie drink. NCCIH reports no safety concerns for adults drinking it, though it contains caffeine and can interact with some medicines.
Does green tea have caffeine?
Yes. A typical serving has less caffeine than black tea or brewed coffee in FDA’s table, but the amount varies by product and brewing. Decaffeinated versions are available.
What are green tea side effects?
As a drink, side effects mostly relate to caffeine, such as jitters or poor sleep. Extract supplements have been linked to nausea, constipation, raised blood pressure and rare liver injury.
Is green tea the same as green tea extract?
No. Extracts concentrate catechins far beyond a cup of tea, and nearly all liver injury reports involve extracts in capsules or tablets rather than brewed tea.
Can green tea interact with medicines?
Yes. Large amounts can lower levels of the beta-blocker nadolol, and green tea or its extract has interacted with atorvastatin and raloxifene. Ask your pharmacist if you take any regular medicine.
Questions about a label? Contact us or read our Buyer’s Guide. Follow the label and ask a healthcare provider before starting any supplement, especially if you take medicines or are pregnant. These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
Last reviewed October 2026.
Related guides: Green Tea Extract and EGCG: Caffeine, Weight Research and Liver Safety, Matcha Benefits: Caffeine, L-Theanine and What Studies Show, L-Theanine Benefits, Side Effects and the Caffeine Combination.