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Green Tea

Camellia sinensis
Evidence Level
Strong
7 Clinical Trials
5 Documented Benefits
4/5 Evidence Score

Green tea comes from the leaves of Camellia sinensis and is rich in catechins, especially epigallocatechin gallate (EGCG), along with caffeine. As a supplement it is used mainly for weight management, antioxidant support and healthy cholesterol. Pooled trials show small effects: about 1.3 kg more weight loss than control with catechin products, and drops of about 7 mg/dL in total cholesterol and 2 to 6 mg/dL in LDL cholesterol. Green tea raises blood antioxidant markers, but large pooled analyses found no effect on most inflammation markers, including CRP. Matcha trials on attention and memory are few and inconsistent. Concentrated extracts, unlike brewed tea, have been linked in rare cases to liver injury, so take them with food, and catechins can modestly reduce iron absorption.

Studied Dose Trials cited here used 146 mg/day EGCG (with hesperidin) and 400 mg/day decaffeinated green tea polyphenols; an iron absorption study tested 150 to 300 mg/day pure EGCG. Liver injury reports with extracts span about 140 to 1,000 mg/day EGCG, so take extracts with food.
Active Compound Catechins, mainly epigallocatechin gallate (EGCG), plus caffeine.

Benefits

Antioxidant Properties

Catechins such as EGCG neutralize free radicals in laboratory tests. In pooled human trials, green tea supplements raised total antioxidant capacity and improved markers such as malondialdehyde, superoxide dismutase and glutathione peroxidase. These are blood markers; a large review found the evidence too inconsistent to recommend green tea for cancer prevention.

Supported by Trial 7, Trial 2

Weight Management Support

A meta-analysis of 11 studies found catechins, or EGCG mixed with caffeine, gave about 1.3 kg more weight loss, or better weight maintenance, than control. The effect looked smaller in people who habitually take in over 300 mg of caffeine a day, although that difference was not statistically significant. It is a small add-on to diet and activity, not a substitute.

Supported by Trial 1, Trial 2

Cardiovascular Health

In a meta-analysis of 14 randomized trials, green tea lowered total cholesterol by about 7 mg/dL and LDL cholesterol by about 2 mg/dL, with no HDL change. A pooled analysis of 55 trials found similar cholesterol drops, a diastolic blood pressure drop under 1 mmHg and no significant change in systolic pressure. These are small shifts in risk markers, not proof of fewer heart attacks or strokes.

Supported by Trial 3, Trial 2

Cognitive Function

Human evidence on thinking skills is thin. A review of matcha, the powdered whole-leaf form of green tea, found only a few randomized trials, with less stress and slightly better attention and memory in some but contradictory results overall. Brain-protective effects of EGCG come from laboratory and animal studies and have not been shown in people.

Supported by Trial 2, Trial 3

Inflammation Markers: IL-1 Beta Lowered, CRP Unchanged

A pooled analysis of 38 randomized trials found green tea lowered one inflammatory marker, IL-1 beta, slightly, but had no significant effect on CRP, IL-6 or TNF-alpha. A separate analysis also found no CRP change, and a 45-day trial saw no change in inflammation markers. This is weak evidence for any anti-inflammatory effect.

Supported by Trial 7, Trial 3

Mechanism of action

1

Antioxidant Activity

In laboratory studies, catechins, especially EGCG, scavenge free radicals. In pooled human trials, green tea raised total antioxidant capacity and improved the antioxidant enzymes superoxide dismutase and glutathione peroxidase; these are blood markers rather than health outcomes.

2

Energy Use and Fat Burning

In a pooled analysis of six respiration-chamber studies, catechin and caffeine mixtures raised 24-hour energy expenditure by about 4.7% and fat burning by about 16% compared with placebo; caffeine alone raised energy expenditure by a similar amount but did not significantly raise fat burning. In weight-loss trials the net effect was small, about 1.3 kg more than control.

3

Cardiovascular Benefits

Catechins are proposed to reduce cholesterol absorption in the gut and to support blood vessel function. The changes measured in human trials are small: total cholesterol fell about 7 mg/dL and diastolic blood pressure fell by less than 1 mmHg.

4

Brain-Active Compounds

Green tea contains caffeine, which increases alertness, and L-theanine, an amino acid studied for attention on its own and together with caffeine. EGCG has been reported to cross the blood-brain barrier, and its brain-protective effects come from laboratory and animal studies, not human trials.

5

Anti-Inflammatory and Immune Modulation

In laboratory studies, catechins inhibit pro-inflammatory pathways such as NF-kB and modulate immune cell activity. In human trials, however, most blood inflammation markers did not change.

Clinical trials

1
Green Tea Catechins Plus Glucosyl Hesperidin and Body Weight
PubMed

Randomized, double-blind, placebo-controlled, parallel-group trial in Japan. Daily green tea providing 146 mg EGCG combined with 178 mg alpha-glucosyl hesperidin, or placebo, for 12 weeks. Designed and funded by Toyota Motor Corporation, which has a patent pending with Kyushu University. (Yoshitomi et al. 2021, Sci Rep)

60 healthy Japanese men and women aged 30 to 75.

At 12 weeks the combination prevented weight gain and lowered BMI compared with placebo, and safety tests showed no problems. Body fat and visceral fat fell mainly in people under 50. Because two ingredients were combined, the effect cannot be credited to green tea alone.

2
Green Tea and Antioxidant Status: Meta-Analysis of 16 Trials
PubMed

Systematic review and meta-analysis of randomized trials measuring total antioxidant capacity (TAC) and malondialdehyde (MDA), a marker of oxidative damage to fats, using a random-effects model. (Rasaei et al. 2021, Antioxidants (Basel))

16 randomized trials (17 arms) with 760 adults.

Green tea raised total antioxidant capacity by 0.20 mmol/L (95% CI 0.09 to 0.30), with very high heterogeneity between studies. Overall MDA did not change, although higher doses were linked to larger MDA drops in a meta-regression. These are blood markers, not health outcomes.

3
Green Tea and Cardiovascular Risk Factors: Meta-Analysis of 55 Trials
PubMed

Systematic review and meta-analysis of randomized trials of green tea supplementation on blood lipids, blood pressure, blood sugar markers and CRP, using a random-effects model. (Zamani et al. 2022, Front Nutr)

55 randomized trials with 63 effect sizes.

Green tea lowered total cholesterol by 7.62 mg/dL, LDL cholesterol by 5.80 mg/dL and diastolic blood pressure by 0.87 mmHg, slightly lowered fasting blood sugar and HbA1c, and raised HDL cholesterol by 1.85 mg/dL. Systolic blood pressure and CRP did not change significantly. The changes are small.

4
Decaffeinated Green Tea Polyphenols in Girls: 12-Week Safety Trial
PubMed

Randomized, double-blind, placebo-controlled trial in China. 400 mg/day decaffeinated green tea polyphenols or placebo for 12 weeks; the main aim was safety. (Yao et al. 2024, Asia Pac J Clin Nutr)

62 girls aged 6 to 10 with obesity (31 per group).

Liver and kidney markers, blood minerals and blood counts did not differ between groups, and no adverse effects were reported. Uric acid fell more with the polyphenols but stayed in the normal range. A trial this small cannot detect rare liver injury, so it does not show that extracts are safe for children in general.

5
Green Tea Tablets, Body Measures and Inflammation Markers: 45-Day Trial
PubMed

Randomized clinical trial of green tea tablets or placebo for 45 days, measuring weight, BMI, waist, body fat and the inflammation markers IL-6, hs-CRP and TNF-alpha. (Mombaini et al. 2017, Phytother Res)

45 women with polycystic ovary syndrome (PCOS).

Weight, BMI, waist and body fat fell within the green tea group, but the differences between green tea and placebo were not significant. Inflammation markers did not change. Both outcomes were null versus placebo.

6
Green Tea and Liver Enzymes: Meta-Analysis of 4 Trials
PubMed

Systematic review and meta-analysis of clinical trials of green tea supplementation in adults with nonalcoholic fatty liver disease (NAFLD). (Mansour-Ghanaei et al. 2018, Phytother Res)

Four clinical trials in adults with NAFLD.

Green tea lowered the liver enzymes ALT (by 12.81 U/L) and AST (by 10.91 U/L), and also BMI, triglycerides, total cholesterol and LDL cholesterol, with no significant change in HDL cholesterol or insulin resistance. Only four trials were pooled.

7
Green Tea, Antioxidant and Inflammation Markers: Meta-Analysis of 38 Trials
PubMed

GRADE-assessed systematic review and dose-response meta-analysis of randomized controlled trials. (Dehzad et al. 2025, J Nutr Sci)

38 randomized trials in adults.

Green tea improved IL-1 beta, MDA, total antioxidant capacity, superoxide dismutase and glutathione peroxidase, but had no significant effect on CRP, IL-6 or TNF-alpha. The authors concluded that green tea can improve oxidative status but showed no significant effect on inflammatory markers except IL-1 beta.

Side effects and drug interactions

Common Potential side effects

Digestive and other effects: green tea extract supplements can cause nausea, constipation, abdominal discomfort and a rise in blood pressure.
Liver Toxicity: Concentrated green tea extracts, not brewed tea, have been linked to rare but sometimes serious liver injury. A United States Pharmacopeia review of this evidence found case reports across EGCG intakes of roughly 140 to 1,000 mg/day with marked variation in individual susceptibility, and recommended a cautionary statement on green tea extract labels. Taking an extract while fasting raises how much EGCG reaches the blood, so take it with food and keep the dose moderate. The USP label warning also says not to use green tea extract if you have a liver problem, and to stop and consult a healthcare practitioner if signs of liver trouble appear, such as abdominal pain, dark urine or jaundice (yellowing of the skin or eyes).
Caffeine-Related Effects: Green tea contains caffeine unless decaffeinated. Too much caffeine can cause a faster heart rate, palpitations, higher blood pressure, trouble sleeping, anxiety, jitters, upset stomach, nausea and headache. In pregnancy keep caffeine intake moderate; caffeine passes into breast milk, and high intake can make breastfed infants fussy and sleep poorly.
Iron Absorption Interference: In women with low iron stores, 300 mg of pure EGCG reduced iron absorption by 27% (a 14% drop at 150 mg was not statistically significant); black tea drunk with a meal reduced it far more in another study. People with low iron should take iron at a different time from green tea products.

Important Drug interactions

Nadolol, atorvastatin and raloxifene: green tea at high doses lowered blood levels of the beta-blocker nadolol, green tea extract can lower blood levels of atorvastatin, and an interaction with raloxifene has been reported. Tell your prescriber if you take these.
Iron supplements: in a controlled study, 300 mg of pure EGCG cut iron absorption by 27% (150 mg gave a smaller, non-significant drop); take green tea extract and iron at separate times.
Other medicines: green tea may also interact with medicines not listed here, and some medications make people more sensitive to caffeine. If you take any medicine, talk with your health care provider before using green tea supplements.
Liver problems and liver-affecting medicines: the USP label warning says not to use green tea extract if you have a liver problem. Because extracts have been linked to rare liver injury, ask your doctor before combining them with medicines that can affect the liver.

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Frequently asked questions about Green Tea

How much green tea should I drink?

There is no single proven amount. Brewed green tea supplies catechins (including EGCG), L-theanine and caffeine. Extract studies cited on this page used roughly 146 to 400 mg/day of EGCG or green tea polyphenols; take extracts with food and follow the label.

How much caffeine is in green tea?

The caffeine in a cup of green tea varies with the leaves and how long it is brewed, and is usually lower than in a cup of coffee. Green tea also contains L-theanine, an amino acid. Concentrated extracts may contain more caffeine or be decaffeinated, so check the label.

What is green tea good for?

Green tea is studied for antioxidant support, weight management, heart health and attention. The effects measured in trials are small, and it is not established for preventing any disease. Its main active compounds are catechins such as EGCG, alongside L-theanine and caffeine.

Is it better to drink green tea or take an extract?

Brewed green tea is a common beverage that also provides L-theanine. Concentrated extracts deliver more EGCG for those targeting specific benefits, but concentrated extracts carry a rare risk of liver injury that brewed tea does not. The USP review behind current cautionary labeling recommends taking green tea extract with food rather than on an empty stomach. Keep the dose moderate, avoid stacking it with other liver-stressing products, and stop immediately and see a clinician if jaundice, dark urine or abdominal pain develops.

Is matcha the same as green tea?

Matcha is green tea (Camellia sinensis) in powdered form. The tea bushes are traditionally shaded for much of the growing period, which raises theanine and chlorophyll in the leaves, and the leaves are then ground into a fine powder that is whisked with water, so you drink the whole leaf rather than an infusion. Matcha also tends to carry more caffeine than steeped green tea, partly because it is made from young leaves, which hold more caffeine than mature ones. Matcha itself has been tested in relatively few randomized trials, with small and inconsistent effects on attention and memory, so most of the research on this page comes from brewed green tea and green tea extracts rather than from matcha.

What is Green Tea?

Green tea comes from the leaves of Camellia sinensis and is rich in catechins, especially epigallocatechin gallate (EGCG), along with caffeine. As a supplement it is used mainly for weight management, antioxidant support and healthy cholesterol. Pooled trials show small effects: about 1.

What is Green Tea used for?

Green Tea is researched primarily for Antioxidant, Weight Management, and Cognitive. Catechins such as EGCG neutralize free radicals in laboratory tests. In pooled human trials, green tea supplements raised total antioxidant capacity and improved markers such as malondialdehyde, superoxide dismutase and glutathione peroxida…

What is the recommended dosage of Green Tea?

The clinically studied dose is Trials cited here used 146 mg/day EGCG (with hesperidin) and 400 mg/day decaffeinated green tea polyphenols; an iron absorption study tested 150 to 300 mg/day pure EGCG. Always follow the product label and check with a healthcare provider for personal advice.

Is Green Tea safe, and does it have side effects?

Side effects and cautions reported for Green Tea include: Digestive and other effects: green tea extract supplements can cause nausea, constipation, abdominal discomfort and a rise in blood pressure. Liver Toxicity: Concentrated green tea extracts, not brewed tea, have been linked to rare but sometimes serious liver injury. It may also interact with some medications. Green Tea is not right for everyone, so check with a healthcare provider first if you are pregnant or breastfeeding, have a medical condition, or take prescription medication.

Does Green Tea interact with any medications?

Possible interactions include: Nadolol, atorvastatin and raloxifene: green tea at high doses lowered blood levels of the beta-blocker nadolol, green tea extract can lower blood levels of atorvastatin, and an interaction with raloxifene has been reported. Tell your prescriber if you take these. If you take prescription medication, check with a pharmacist or doctor before using it.

How strong is the scientific evidence for Green Tea?

NutraSmarts rates the evidence for Green Tea as Strong (4 out of 5). It is backed by 7 study summaries and 17 cited references summarized on this page. A higher rating reflects more, larger, and better-designed human studies.

References(17 citations)

Evidence ratings on NutraSmarts are based on the totality of human clinical research, with emphasis on randomized controlled trials, meta-analyses, and systematic reviews. The references below directly support claims made throughout this page.

  1. Hursel R, Viechtbauer W, Westerterp-Plantenga MS. The effects of green tea on weight loss and weight maintenance: a meta-analysis. Int J Obes (Lond). 2009;33(9):956-61. doi: 10.1038/ijo.2009.135.PubMedUsed to support: Meta-analysis of 11 studies: catechins or EGCG-caffeine mixtures reduced body weight and helped weight maintenance by about 1.31 kg versus control. The smaller effect with high habitual caffeine intake and in Caucasians did not reach significance on its own, though the caffeine-ethnicity interaction did.
  2. Zheng XX, Xu YL, Li SH, Liu XX, Hui R, Huang XH. Green tea intake lowers fasting serum total and LDL cholesterol in adults: a meta-analysis of 14 randomized controlled trials. Am J Clin Nutr. 2011;94(2):601-10. doi: 10.3945/ajcn.110.010926.PubMedUsed to support: Lipid meta-analysis (14 RCTs, 1,136 subjects): green tea significantly lowered total cholesterol (~7.2 mg/dL) and LDL-C (~2.2 mg/dL) vs control, with no significant change in HDL-C. Statistically significant but small absolute reductions.
  3. Filippini T, Malavolti M, Borrelli F, Izzo AA, Fairweather-Tait SJ, Horneber M, Vinceti M. Green tea (Camellia sinensis) for the prevention of cancer. Cochrane Database Syst Rev. 2020;3(3):CD005004. doi: 10.1002/14651858.CD005004.pub3.PubMedUsed to support: Cochrane review: experimental and epidemiological studies on green tea and cancer gave inconsistent, conflicting results, so green tea cannot be recommended for cancer prevention.
  4. Oketch-Rabah HA, Roe AL, Rider CV, Bonkovsky HL, Giancaspro GI, Navarro V, Paine MF, Betz JM, Marles RJ, Casper S, Gurley B, Jordan SA, He K, Kapoor MP, Rao TP, Sherker AH, Fontana RJ, Rossi S, Vuppalanchi R, Seeff LB, Stolz A, Ahmad J, Koh C, Serrano J, Low Dog T, Ko R. United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts. Toxicol Rep. 2020;7:386-402. doi: 10.1016/j.toxrep.2020.02.008.PubMedUsed to support: Safety (liver): USP systematic review underpinning current cautionary labeling. Hepatotoxicity case reports are associated with EGCG intakes ~140-1000 mg/day with marked inter-individual susceptibility. Its label statement says to take green tea extract with food, not on an empty stomach, not to use it with a liver problem, and to stop and consult a healthcare practitioner if abdominal pain, dark urine or jaundice develops.
  5. Sokary S, Al-Asmakh M, Zakaria Z, Bawadi H. The therapeutic potential of matcha tea: A critical review on human and animal studies. Curr Res Food Sci. 2023;6:100396. doi: 10.1016/j.crfs.2022.11.015.PubMedUsed to support: Review explaining that matcha is powdered Japanese green tea from bushes shaded for most of the growing period, so the whole leaf is consumed; matcha holds more caffeine because buds and young leaves contain more caffeine than mature leaves; EGCG has been reported to cross the blood-brain barrier and L-theanine is studied for attention; its few randomized trials suggest less stress and slightly better attention and memory with contradictory cognitive results; cardio-metabolic effects have only been studied in animals.
  6. Ullmann U, Haller J, Bakker GC, Brink EJ, Weber P. Epigallocatechin gallate (EGCG) (TEAVIGO) does not impair nonhaem-iron absorption in man. Phytomedicine. 2005;12(6-7):410-5. doi: 10.1016/j.phymed.2004.07.001.PubMedUsed to support: Randomized, double-blind, placebo-controlled crossover study in 30 women with low iron stores. Pure EGCG reduced non-heme iron absorption by 27% at 300 mg, a statistically significant drop versus placebo; the 14% drop at 150 mg was not significantly different from placebo. The authors judged the effect much smaller than reported for black tea.
  7. Hurrell RF, Reddy M, Cook JD. Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. Br J Nutr. 1999;81(4):289-95..PubMedUsed to support: Human iron absorption study: polyphenol-containing drinks served with a bread meal reduced non-heme iron absorption in a dose-dependent way, and black tea reduced it by 79 to 94%.
  8. Yoshitomi R, Yamamoto M, Kumazoe M, Fujimura Y, Yonekura M, Shimamoto Y, Nakasone A, Kondo S, Hattori H, Haseda A, Nishihira J, Tachibana H. The combined effect of green tea and α-glucosyl hesperidin in preventing obesity: a randomized placebo-controlled clinical trial. Sci Rep. 2021;11(1):19067. doi: 10.1038/s41598-021-98612-6.PubMedUsed to support: Randomized, double-blind, placebo-controlled trial in 60 healthy Japanese adults: green tea with 146 mg EGCG plus 178 mg alpha-glucosyl hesperidin for 12 weeks prevented weight gain and lowered BMI versus placebo; funded by Toyota Motor Corporation.
  9. Rasaei N, Asbaghi O, Samadi M, Setayesh L, Bagheri R, Gholami F, Soveid N, Casazza K, Wong A, Suzuki K, Mirzaei K. Effect of Green Tea Supplementation on Antioxidant Status in Adults: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. Antioxidants (Basel). 2021;10(11):1731. doi: 10.3390/antiox10111731.PubMedUsed to support: Meta-analysis of 16 randomized trials (760 adults): green tea raised total antioxidant capacity by 0.20 mmol/L; MDA did not change overall but fell more at higher doses in meta-regression.
  10. Zamani M, Kelishadi MR, Ashtary-Larky D, Amirani N, Goudarzi K, Torki IA, Bagheri R, Ghanavati M, Asbaghi O. The effects of green tea supplementation on cardiovascular risk factors: A systematic review and meta-analysis. Front Nutr. 2022;9:1084455. doi: 10.3389/fnut.2022.1084455.PubMedUsed to support: Meta-analysis of 55 randomized trials: green tea lowered total cholesterol (7.62 mg/dL), LDL (5.80 mg/dL), fasting blood sugar, HbA1c and diastolic blood pressure (0.87 mmHg) and raised HDL; systolic blood pressure and CRP did not change significantly.
  11. Yao D, Xie L, Du K, Yao X, Shen X. Decaffeinated green tea polyphenols supplementation had no adverse health effects in girls with obesity: a randomized controlled trial. Asia Pac J Clin Nutr. 2024;33(1):111-117. doi: 10.6133/apjcn.202403_33(1).0012.PubMedUsed to support: 12-week randomized, double-blind trial in 62 girls aged 6 to 10 with obesity: 400 mg/day decaffeinated green tea polyphenols caused no adverse effects or differences in liver, kidney or blood markers versus placebo, apart from a larger uric acid drop within the normal range.
  12. Mombaini E, Jafarirad S, Husain D, Haghighizadeh MH, Padfar P. The Impact of Green Tea Supplementation on Anthropometric Indices and Inflammatory Cytokines in Women with Polycystic Ovary Syndrome. Phytother Res. 2017;31(5):747-754. doi: 10.1002/ptr.5795.PubMedUsed to support: 45-day randomized trial in 45 women with PCOS: green tea tablets reduced weight measures within the group, but not significantly versus placebo, and did not change IL-6, hs-CRP or TNF-alpha.
  13. Mansour-Ghanaei F, Hadi A, Pourmasoumi M, Joukar F, Golpour S, Najafgholizadeh A. Green tea as a safe alternative approach for nonalcoholic fatty liver treatment: A systematic review and meta-analysis of clinical trials. Phytother Res. 2018;32(10):1876-1884. doi: 10.1002/ptr.6130.PubMedUsed to support: Meta-analysis of four clinical trials in adults with NAFLD: green tea lowered ALT, AST, BMI, triglycerides, total and LDL cholesterol, with no significant change in HDL or HOMA-IR.
  14. Dehzad MJ, Ghalandari H, Nouri M, Makhtoomi M, Askarpour M. Effects of green tea supplementation on antioxidant status and inflammatory markers in adults: a grade-assessed systematic review and dose-response meta-analysis of randomised controlled trials. J Nutr Sci. 2025;14:e25. doi: 10.1017/jns.2025.13.PubMedUsed to support: Meta-analysis of 38 randomized trials: green tea improved IL-1 beta, MDA, total antioxidant capacity, SOD and GPX, but had no significant effect on CRP, IL-6 or TNF-alpha.
  15. National Center for Complementary and Integrative Health, National Institutes of Health. Green Tea NCCIH (NIH). 2025;Online fact sheet, last updated February 2025..SourceUsed to support: Not PubMed-indexed (NIH fact sheet). Lists nausea, constipation, abdominal discomfort and increased blood pressure as side effects of green tea extract supplements; reports uncommon liver injury mainly with extracts; states that green tea at high doses reduced blood levels of the beta-blocker nadolol, that green tea extract can reduce blood levels of atorvastatin, and notes an interaction with raloxifene; adds that green tea may also interact with other medicines, that green tea is a source of caffeine, that caffeine intake in pregnancy should not exceed moderate levels, and that caffeine passes into breast milk, where high intake can cause fussiness and poor sleep in infants.
  16. Hursel R, Viechtbauer W, Dulloo AG, Tremblay A, Tappy L, Rumpler W, Westerterp-Plantenga MS. The effects of catechin rich teas and caffeine on energy expenditure and fat oxidation: a meta-analysis. Obes Rev. 2011;12(7):e573-81. doi: 10.1111/j.1467-789X.2011.00862.x.PubMedUsed to support: Meta-analysis of six respiration-chamber studies (18 conditions): catechin and caffeine mixtures raised 24-hour energy expenditure by 428 kJ (4.7%) and fat oxidation by 12.2 g (16.0%) versus placebo; caffeine alone raised energy expenditure by 429 kJ (4.8%), but its 12.4% rise in fat oxidation was not significant. Both effects were dose-dependent.
  17. U.S. Food and Drug Administration. Spilling the Beans: How Much Caffeine is Too Much? FDA Consumer Updates. 2024;Online consumer update, content current as of August 28, 2024..SourceUsed to support: Not PubMed-indexed (FDA consumer update). States that the FDA has cited 400 mg a day as an amount not generally associated with negative effects for most adults; lists signs of too much caffeine (increased heart rate, palpitations, high blood pressure, insomnia or sleep disruption, anxiety, jitters, upset stomach, nausea, headache); notes that some conditions and medications make people more sensitive to caffeine and advises talking with a health care provider about limiting caffeine in pregnancy, when trying to become pregnant or while breastfeeding; and estimates that about 1,200 mg taken quickly, less than half a teaspoon of pure caffeine, can cause toxic effects such as seizures.