Green Tea Side Effects: They Exist But Don’t Be Afraid!


Although green tea has many health benefits some serious green tea side effects also exist.

These side effects only occur, if at all, when consumption is high, during a longer period of time. After all, the United States Food and Drug Administration (FDA) wouldn’t categorize green tea as “Generally Recognized as Safe“.

Most of the negative green tea side effects are associated with the caffeine content in green tea.

Green tea side effects: caffeine, the scapegoat.

Some of the negative side effects related to excessive caffeine consumption during a longer period of time are:

  • green-tea-side-effectsInsomnia (unable to fall asleep)
  • Restlessness
  • Anxiety
  • Irritability
  • Upset stomach (gas)
  • Nausea
  • Headaches (from dehydration)
  • Tremor (uncontrollable muscle contraction and relaxation)
  • Loss of appetite
  • Diarrhea
  • Vomiting
  • Heart palpitations (a rapidly or forcefully beating heart)
  • Irregular heart rhythm (arrhythmia)
  • Increased blood sugar levels
  • Dizziness
  • Frequent urination.

Green tea side effects: the rest……

Other green tea side effects are:

1. Allergic reactions

People can be allergic to green tea ingredients such as the tannins or caffeine, identified through unexplained skin rash, hives, itching, swelling of the mouth or throat, wheezing, or difficulty breathing or swallowing.

These exceptional allergic reactions are similar to, say, a peanut, bee sting, or shrimp allergy.

2. Health issues

Some health issues may occur when drinking green tea, such as:

  • Iron deficiency anemia. Polyphenols (mainly tannins and catechins) found in green tea bind to non-heme iron. Although this anti-oxidative effect is desirable in the fight against cancer,this mechanism may impair the utilization of dietary iron. In other words, polyphenols lower the iron availability and absorption from foods; green tea extract decreased non-heme iron absorption by 28%.Two independent studies involving children from different ends of the world (Great Britain and Saudi Arabia) found they may optimize their iron status by avoiding tea with (or after) meals. The interaction between tea and iron can be mitigated, however, by the addition of high sources of vitamin C or consuming tea between meals.Conversely, a 1998 study argued that the reduction in iron absorption may be of benefit to patients with genetic haemochromatosis.
  • Thiamine deficiency. Another potential green tea side effect is that green tea reduces the absorption of thiamine (vitamin B), which can lead to a condition known as Beriberi (nowadays known primarily to alcoholics, people on fad diets, or persons undergoing long-term starvation) where one version attacks the cardiovascular system and another version attacks the neurologic system.
  • Liver disorders. In rare cases, green tea extract may lead to acute liver toxicity, recognized by abdominal pain, dark urine, or jaundice.
  • Kidney problems. Green tea overconsumption may affect the absorption of oxalates and contribute to the development of kidney stones. Contrary to these results, Curhan et al found drinking tea
    (a daily serving of 240 ml) decreases the risk of developing kidney stones by 8%; a study involving more than 81,000 women.
  • Stomach problems. Dubey concluded in a 1984 study that “tea is a potent stimulant of gastric acid, and this can be reduced by adding milk and sugar.”
  • Teeth stains. Green tea will stain your teeth if you do not brush your teeth within 24 hours and floss regularly. Check out: does green tea stain teeth.
  • Beware of diet teas. There are two types of diet teas: the good and the bad. Beware of the second one containing mostly stimulant laxative herbs; when consumed in large quantities these laxative herbs may lead to (chronic) diarrhea, nausea, vomiting, stomach bleeding/cramps, fainting, dehydration and (chronic) constipation. Read more on Chinese diet teas.
  • Pregnant or breastfeeding women. Caffeine, catechins and tannic acids are substances linked to pregnancy risks such as miscarriages, low birth weights and fetal neural tube defects. Some health organizations advise pregnant women to limit their caffeine consumption to 300 mg per day. Read more on green tea and pregnancy.

3. Interference with medications

If you are on medication or you have a medical history always consult your medical advisor whether or not to take green tea as it may interfere or interact with certain medications such as antibiotics, sedatives, beta blockers (adenosine), blood thinners (aspirin or warfarin), anti-psychotics (MAOIs, clozapine, or lithium), some cough, cold, and weight loss products.


Tips (to prevent green tea side effects)

Here are some tips to limit possible negative green tea side effects.

  • Use green tea in moderate amounts.
  • Brew between 160-180 degrees Fahrenheit (just below boiling point) to prevent green tea changing into an acidic, astringent chemical composition otherwise contributing to acid reflux (heartburn) and an upset stomach).
  • Avoid making your cup of green tea too strong; a strong cup contains more caffeine (and polyphenols) which can lead to the side effects mentioned earlier.
  • Avoid drinking green tea for at least 2 hours after taking medications.
  • Avoid or only consume moderate amounts of green tea during pregnancy or breastfeeding.

Read more on the BENEFITS of green tea!

Read more on the CAFFEINE CONTENT in green tea.

Read more on POLYPHENOLS; an important green tea ingredient.

Return to green tea FACTS.

Return from green tea side effects to the HOME page.

Sources “green tea side effects”

Al-Othaimeen A, Osman A, Al-Orf S: Prevalence of nutritional anaemia among primary school girls in Riyadh City, Saudi Arabia. Int J Food Sci Nutr 50:237 –243, 1999.

Cabrera C, Artacho R, Giménez R. Beneficial effects of green tea – a review. Journal of the American College of Nutrition, 25(2):79-99, 2006.

Curhan GC, Willet WC, Speizer FE, Stampfer MJ. Beverage use and risk for kidney stones in women. Annals of Internal Medicine, 128:534-540, 1998.

Dubey P, Sundram KR, Nundy S. Effect of Tea on Gastric Acid Secretion. Digestive Diseases and Sciences, (29)3:202-206, 1984.

Gibson S: Iron intake and iron status of preschool children: Associations with breakfast cereals, vitamin C and meat. Public Health Nutr, 2:521 –528,1999.

Hamdaoui MH, Chabchob S, Heidhili A: Iron bioavailability and weight gains to iron-deficient rats fed a commonly consumed Tunisian meal “bean seeds ragout” with or without beef and with green or black tea decoction. Journal of Trace Elements in Medicine and Biology, 17:159 –164, 2003.

Kaltwasser JP, Werner E, Schalk K, Hansen C, Gottschalk R, Seidl C. Clinical trial on the effect of regular tea drinking on iron accumulation in genetic haemochromatosis. International Journal of Gastroenterology and Hepatology, 43:699-704, 1998.

Massey L. Tea oxalate. Nutrition Reviews 58:88-89, 2000.

McKay DL, Blumberg JB. The Role of Tea in Human Health: An Update. Journal of the American College of Nutrition, 21(1):1–13, 2002.

Molinari M, Watt KDS, Kruszyna T, Nelson R, Walsh M, Huang WY, Nashan B and Peltekian K. Acute Liver Failure Induced by Green Tea Extracts: Case Report and Review of theLiterature. Liver Transplantation, 12:1892-1895, 2006.

Samman S, Sandström B, Toft MB, Bukhave K, Jensen M, Sørensen SS, Hansen M. Green tea or rosemary extract added to foods reduces nonheme-iron absorption. American Journal of Clinical Nutrition, 73:607-12, 2001.

Tuntawiroon M, Sritongkul N, Brune M, Rossander-Hultén L, Pleehachinda R, Suwanik R and Hallberg L. Dose-dependent inhibitory effect of phenolic compounds in foods on nonheme-iron absorption in men. American Journal of Clinical Nutrition, 53:554-7, 1991.