15 Side Effects of Green Tea

Green tea is well-known for its numerous health advantages. It is also regarded as one of the healthiest beverages. But did you know that green tea has some negative effects as well? The Camellia sinensis plant is used to make this healthful tea. EGCG (epigallocatechin gallate), a chemical found in green tea, can help people lose weight and reduce their risk of cancer and cardiovascular disease. Green tea, on the other hand, might be harmful to your health if consumed in excess.

Side Effects of Green Tea

Green tea consumption in excess has negative consequences. Here’s a rundown of the 15 side effects to watch out for.

green tea side effects

(1) Green Tea Caffeine Interferes With Some Medications

Caffeine is a stimulant of the central nervous system. That is why a cup of green tea revitalizes and re-energizes you. The catch is that drinking a lot of green tea while taking certain drugs can induce negative side effects.

Caffeine is broken down and drained out of the body. However, certain medications such as Cimetidine, antibiotics such as Ciprofloxacin, enoxacin (Penetrex), trovafloxacin (Trovan), sparfloxacin (Zagam), norfloxacin (Chibroxin, Noroxin), grepafloxacin (Raxar), Fluconazole, anesthetics such as Midazolam, and birth control pills inhibit caffeine breakdown.

Caffeine remains in the body as a result, causing jitters, restlessness, an increase in heart rate, and, in some circumstances, arrhythmia.

Green tea caffeine impeded the metabolism of Clozapine, an antipsychotic medicine, resulting in clozapine toxicity, according to researchers. Green tea should likewise be avoided by lithium users.

Warfarin, an anticoagulant (blood clotting) medicine, is inhibited by vitamin K in green tea, according to research.

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(2) Green Tea Caffeine Can Cause Hypokalemia And Seizures

Low potassium levels in the blood are a sign of hypokalemia. Potassium is required for muscle contraction and protein activity in the body. Drinking too much green tea can cause potassium deficiency, which can cause muscle weakness, spasms, cramps, and irregular heart rhythms.

Green tea consumption was advised to be reduced in two patients with hypokalemia (low potassium levels). After a few days, their potassium levels returned to normal due to this modification alone. Green tea, on the other hand, was proven to cause hypokalemia when taken with other drugs. In a research published in the British Medical Journal, it was discovered that drinking green tea alone did not cause this effect.

Green tea’s potassium- and calcium-lowering characteristics may also have a pre-convulsive (muscle tremor and epilepsy) effect, according to researchers.

Other research suggests that taking more than 200 mg of green tea per day may raise the risk of seizures and the frequency with which they occur, Caffeine appears to raise the risk of seizures in certain studies, but more research is needed. Caffeine, on the other hand, was found to diminish the efficacy of epilepsy medicines in a study published in Epilepsy & Behavior.

According to other research, patients with epilepsy who ingested large amounts of coffee saw an increase in seizure frequency.

(3) Caffeine Toxicity

Caffeine poisoning can occur if you consume more than 400 mg of caffeine each day. Headaches, nausea, vomiting, chills, palpitations, and flushing are common symptoms of caffeine intoxication.

Caffeine in higher quantities might cause blood pressure to drop below normal. People who are caffeine sensitive, on the other hand, may experience signs of caffeine intoxication even at smaller dosages. There have also been reports of typical dosages of green tea caffeine causing blood pressure to rise.

The use of over-the-counter caffeine pills in combination with other nervous system stimulants is not recommended, according to researchers at Monmouth Medical Center in the United States. Caffeine levels in these tablets or supplements are greater than typical. Taking them can lead to atrial fibrillation and, in severe cases, death.

Caffeine is used to treat migraine headaches. Only a licensed physician can decide on the appropriate amount and duration of caffeine treatment for migraines.

(4) Caffeine in green tea may weaken bones

Excessive caffeine, according to the National Osteoporosis Foundation, can inhibit calcium absorption.

Green tea extract (GTE) or a higher green tea intake reduces bone accumulation rate, increases fracture risk, and lowers bone mineral density in both mice and humans. In the elderly, it may induce bone loss.

Green tea flavonoids have been shown in various studies to be quite good for the bones. Higher doses of green tea, on the other hand, may damage bone development and density in this situation.

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(5) Green tea may help to prevent blood clots.

Warfarin is a commonly prescribed anti-clotting medication used to treat blood clots and lower the risk of heart attack and stroke. Green tea caffeine, according to research, inhibits Warfarin’s activity.

Caffeine decreases the metabolism of Warfarin, according to research. As a result, patients using Warfarin should avoid caffeine-rich items like green tea extracts or drinking a lot of green tea.

Warfarin is inhibited by the vitamin K in green tea.

(6) Frequent Urination

Caffeine in green tea may cause frequent urination.

No, it’s not because you drink more water. Green tea contains caffeine.

Green tea caffeine over 4.5 mg per kg per day induces early urine urgency and even increases the frequency. Caffeine’s diuretic effect alters bladder function by causing neural activity to increase.

Green tea in lower quantities may assist to prevent urinary problems.

(7) Green Tea Can Stain Your Teeth

Teeth discoloration is caused by drinking green tea following a teeth whitening treatment. Although no research links green tea consumption to tooth stains, anecdotal evidence suggests that this is the case.

Green tea stains teeth, so avoid it. It’s best to avoid green tea for a few days after a bleaching treatment.

(8) Green tea’s EGCG binds to iron, resulting in anemia and iron deficiency

Anemia is a disease that affects 1.62 billion people globally. It’s caused by iron insufficiency and low hemoglobin levels in the blood.

According to studies, drinking too much green tea regularly might induce iron deficiency, which can lead to anemia and/or a low RBC count.

Dr. Matam Vijay-Kumar, a Penn State assistant professor, says that EGCG (epigallocatechin gallate), specific green tea catechin, binds with iron. This lowers the effectiveness of EGCG as an antioxidant and also prevents iron absorption.

Green tea should not be consumed by persons with IBD (inflammatory bowel disease) who are taking iron supplements, according to Dr. Matam. This is because iron-bound green tea The ability of EGCG to inhibit myeloperoxidase declines (an inflammation-inducing enzyme). This can aggravate IBD by causing inflammation and gastrointestinal pain.

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(9) Drinking Green Tea While Pregnant Can Lead to Birth Defects

Several studies have found that consuming too much green tea during pregnancy can harm both the mother and the baby. Caffeine use of more than 300 mg per day during pregnancy raises the risk of hypertension.

Green tea’s caffeine and tannins have also been proven to lower folic acid levels, according to research. Miscarriages and congenital abnormalities such as spina bifida are prevented by folic acid, a water-soluble B vitamin. Although there is no overall harm linked with tea consumption, the anti-folate effects of green tea need to be investigated further.

Furthermore, excessive use of green tea may increase the chance of premature birth. More research is needed to figure out how green tea might cause this impact.

EGCG, on the other hand, has been shown to prevent neural tube abnormalities caused by maternal diabetes. As a result, it’s important to consult your doctor before drinking green tea while pregnant.

(10) Green Tea Extract Could Harm Your Liver

Green tea is consumed by many people to lose weight and get additional green tea advantages. However, research shows that drinking too much green tea can harm your liver.

Green tea extract contains 10% epigallocatechin gallate (EGCG). Higher EGCG concentrations may produce mitochondrial toxicity, which could result in hepatotoxicity.

After using a weight loss tablet containing a green tea extract, a 37-year-old woman with no history of liver impairment or alcohol use experienced increased inflammation, necrosis (cell or tissue death due to lack of oxygen), and higher aminotransferase levels (a marker of liver damage).

(11) Green Tea Caffeine May Affect Thyroid Function

The catechins in green tea have been shown to lower the risk of thyroid cancer. Caffeine from green tea, on the other hand, may damage thyroid function if consumed in excess. Caffeine intake of 120-150 mg/kg per day during pregnancy has been shown in rat experiments to cause the infant to lose weight (a case of maternal hyperthyroidism).

Green tea drinking may raise the incidence of thyroid cancer in postmenopausal women, according to a study conducted at the National Cancer Center in Tokyo, Japan. In postmenopausal women, on the other hand, it may lessen the same risk.

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(12) Caffeine in green tea may cause anxiety and insomnia.

While moderate dosages of green tea may aid in sleep and stress reduction, bigger doses might cause insomnia and anxiety.

Green tea contains caffeine, which is a nervous system stimulant. Caffeine consumption of more than 300 mg per day has been linked to insomnia, irritability, sadness, aggression, and anxiety.

(13) Excessive use of green tea may cause heartburn.

Heartburn is a common GERD symptom (gastroesophageal disease). Acidity, also known as GERD, is caused by smoking, obesity, poor eating habits, and excessive green tea drinking.

According to Japanese researchers, a sedentary or inactive lifestyle, as well as an excessive intake of green tea regularly, may raise the risk of GERD. Another study on Asian people discovered that theophylline, a component of tea, may cause acid reflux.

Green tea use in excess has been associated with AEE (asymptomatic erosive esophagitis), a type of acid reflux. AEE is 3.8 times more common in persons who drink tea and alcohol at the same time.

(14) Caffeine in green tea may cause stomach upset and pain.

Caffeine has laxative qualities, according to the International Foundation for Gastrointestinal Disorders. If you drink more than three cups of green tea each day, you might have diarrhea.

Green tea extract with high caffeine levels, on the other hand, might produce gastrointestinal pain, jaundice, and dark urine.

(15) Male Infertility

Green tea polyphenols have anti-inflammatory and antioxidant effects. However, in excessive quantities, these can cause male infertility.

Green tea (10 mg/ml) was discovered to lower the reproductive production of Drosophila melanogaster (the common fruit fly) by scientists.

Green tea leaf extract was given to male albino rats for 26 days in a study. The rats’ sperm production, sperm motility, and testosterone levels all decreased after the 26th day (48).

Caffeine in excess can harm sperm DNA and hurt the male reproductive system (49).

These are the 15 scientifically proven green tea adverse effects. So, if greater dosages of green tea are hazardous, what is the appropriate dose? In the next section, you’ll find out.

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How Much Green Tea Do You Need to Drink Every Day?

Green tea should be consumed in moderation, no more than 2-3 cups per day. Also, keep your caffeine intake between 200 and 300 mg/ml. You can drink decaffeinated green tea but keep to the recommended dosage of 2-3 cups per day.

Most adults may be safe with 338 mg of EGCG per day, according to studies.

Check the nutrition label to see how much green tea caffeine or EGCG you’re getting per cup.

Green tea should be avoided by some people. The next portion will inform you who it is.

Who Isn’t Allowed to Drink Green Tea?

Green tea should be avoided if :

  1. You’re expecting a child.
  2. You’re taking Warfarin to keep your blood from clotting (or are taking any other medication).
  3. You’re having problems with your stomach.
  4. You have poor bladder control and a high risk of bladder cancer, and you intend to sleep for an hour.

Note: Consult your doctor to determine whether you should avoid green tea altogether or eat it in small doses.

Is it acceptable to substitute black tea for green tea? In the next part, you’ll find the answer.

Black Tea vs. Green Tea

Some major differences between green tea and black tea are as follows.

  • Camellia sinensis is the same plant that produces both green and black tea. Green tea, on the other hand, is less processed than black tea. This makes a significant difference:
  • Antioxidants are more abundant in green tea than in black tea.
  • Caffeine content is higher in black tea.
  • Both teams are beneficial to one’s health. If you are caffeine sensitive, however, you should drink green tea or matcha tea in moderation (and avoid black tea).

Substitutes for Green Tea

  • Water with lemon
  • Tea with ginger and cinnamon
  • Tea made with chamomile flowers
  • Tea with jasmine flowers
  • Tea with spearmint
  • Tulsi tea is a herb that is used to make tea.

Green tea is well-known for its plethora of health advantages. However, one should be cautious of the negative effects of green tea. Iron deficiency, drug interactions, a higher chance of congenital defects, seizures, headaches, dizziness, vomiting, bone weakness, anxiety, heartburn, and frequent urination are only a few of them. To reduce the hazards, limit your green tea consumption to 2-3 cups per day. Green tea consumption is also potentially dangerous if you have stomach problems, are pregnant, or are at risk of bladder cancer. It is recommended that you use caution.


This article provides general information about the topic and is not to be taken as medical advice or as an alternative to medical advice, treatment, and/or diagnosis. Always consult with your doctor before trying out any of the remedies/recipes suggested in the blog post.

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