Side effects of green tea

Green tea is one of the oldest and most powerful herbal teas available to mankind. It has its roots in China where it was used as a herb during the reign of Emperor Shennong. In modern times, it has gained immense popularity in the west because of its use as an exile. Today’s scientists and researchers have completed studies on the benefits of green tea. Read more about that here. 

About Green Tea

All the teas are made from a plant called Camellia sinensis. Green tea is the least processed tea in terms of true leaves. All the true teas which are not processed contain caffeine. Green tea has been used since ancient times. It also finds its place in Ayurveda in India and in Chinese culture to cure fever and heart diseases. 

Green tea has many health benefits such as aiding weight loss, cancer prevention. Green tea has also been promoted as an alternative to coffee for people who are trying to reduce their caffeine intake. That’s because green tea contains an amino acid known as L-theanine, which helps to regulate blood sugar levels and slows the absorption of caffeine. 

Green tea reacts with free radicals that cause cancer. Oxidative damage has been linked to a host of ailments from reduced insulin sensitivity that may lead to type 2 diabetes and various types of cell damage.

Chemical Composition

The primary compound (Polyphenols) found in green tea is epigallocatechin gallate (EGCG), l-theanine, potassium, iron, calcium, and caffeine. Other components include three kinds of flavonoids, known as kaempferolquercetin, and myricetin. The caffeine content of green tea is about 35 milligrams for every 8-ounce cup, which is considered moderate. The l-theanine present in green tea is responsible for the smooth, steady delivery of caffeine without spikes in blood sugar. Green tea contains b vitamins as well as tannins and folic acid.

Green tea is mostly safe for adults when consumed in moderation. Green tea is considered safe for people when taken orally or applied on the skin for a small period. However, people who are sensitive to caffeine should not drink green tea. 

You can watch this video to find out the side effects of green tea:

Some of the common side effects of green tea

  1. Stomach Problems: Those who are sensitive to teas may have to deal with acidity because of the tannins in the tea. The most common stomach issues are stomach ache, nausea, constipation. Hence, green tea must not be consumed on an empty stomach. Green tea on an empty stomach can lead to absorbing more caffeine which can have effects such as panic, dizziness, weakness in hands and feet, and trance. People who drink tea infrequently, especially on an empty stomach in the morning, are more prone to the above symptoms. This is called Green tea drunkenness. Once green tea drunkenness occurs, it can be relieved by confectionery or drinking some sugar water. You can read the side effects of drinking green tea on an empty stomach here. It is best to drink green tea after a meal or in between meals. People with peptic ulcers or acid reflux should not consume green tea excessively. A 1984 study concluded that tea is a potent stimulant of gastric acid, which can be reduced by adding milk and sugar. Sometimes, improper brewing of green tea may also have adverse effects. Green tea is best brewed with water between 160° and 280° F. Excessively hot water may cause heartburn or an upset stomach.
  2. Iron Deficiency and Anemia: Green tea reduces the absorption of iron from food. The polyphenols in green tea react with iron in the food and less iron is present for the body to absorb. According to an earlier study, green tea was believed to hinder the absorption of animal-based iron by about 25%. However, according to a new study, it reduces the absorption of plant-based iron too. One case study found that green tea caused anaemia in a 48-year-old businessman who consumed 1500 millilitres (6 cups) of green tea every weekday for years (7). However, a quick cheat is to add Vitamin C to your diet. You can squeeze a lemon into your diet i.e. either squeeze a lemon into your green tea or add tomatoes, peas and broccoli to your diet which will increase plant-based iron to your body. 
  3. Mild to serious headaches: According to research done on a large set of population, it was revealed that caffeine leads to headache. Since green tea contains that, even in small quantity, it should be avoided especially by migraine patients. Also Read: Here is a list of herbal teas to reduce headache.  
  4. Sleep problems, nervousness and anxiety: Caffeine blocks sleep-inducing hormones such as melatonin and increases adrenaline production. Therefore, green tea should not be consumed before bedtime. Green tea also contains the amino acid L-theanine, which can calm you down but also make you alert and focus and concentrate better, which is at odds with getting a good night’s sleep. Some research also shows that L-theanine also aids in sleep by lowering heart rate through the inhibition of glutamate receptors in the brain. 
  5.  Irregular or accelerated heartbeat: Caffeine contracts the heart muscles when it is at rest. Caffeine can also lead to an irregular heartbeat.
  6. Vomiting: Green tea because of the presence of caffeine, affects the movement of muscles through the food pipe hence creates nausea. 
  7. Diarrhoea: Green tea because of the presence of caffeine, has a laxative effect. Green tea leads to movement of food pipe hence more contractions and relaxation and hence leads to diarrhoea.
  8. Muscle tremors and contractions: By regulating calcium ion channels within cells, caffeine forces skeletal muscle contractions.
  9. Heartburn: Caffeine releases more acid into your stomach. Hence green tea creates a similar effect to heartburn. 
  10. Dizziness: Green tea can lead to a reduction of the flow of blood to the brain. This in turn leads to dizziness.
  11. Ringing in the ears: Green tea can aggravate tinnitus, which is a condition in which a consistent noise is heard in the ear in the absence of an external source of the sound.
  12. Convulsions: Green tea affects the central nervous system. It activates neurons when consumed in excess, thus, causing convulsions.
  13. Bleeding Disorders: Caffeine in green tea might increase the risk of bleeding.
  14. Diabetes: Caffeine in green tea might interfere with blood sugar control. If you drink green tea and have diabetes, monitor your blood sugar carefully.
  15. Glaucoma: Drinking green tea increases pressure inside the eye. The increase occurs within 30 minutes and lasts for at least 90 minutes.
  16. High Blood Pressure: The caffeine in green tea might increase blood pressure in people with high blood pressure. However, this does not seem to occur in people who regularly drink green tea or other products that contain caffeine.
  17. Liver Disease: Green tea extract supplements have been linked to several cases of liver damage. Green tea extracts might worsen liver disease as the caffeine in the blood may build up and last longer.
  18. Osteoporosis: Drinking green tea can increase the amount of calcium that is flushed out in urine, which can lead to deterioration of bone health and osteoporosis, especially in those who might be predisposed to the same due to other factors. Caffeine should be limited to less than 300 mg per day (approximately 2-3 cups of green tea). It is possible to make up for some calcium loss caused by caffeine by ingesting calcium supplements.
  19. Pregnancy and infant health risks: Green tea contains caffeine, catechins, and tannic acids. All three substances have been linked to pregnancy risks. If you are pregnant or breastfeeding, green tea in small amounts – about 2 cups per day – is safe. This amount of green tea provides about 200 mg of caffeine. However, drinking more than 2 cups of green tea per day has been linked to an increased risk of miscarriage and other negative effects. Caffeine passes into breast milk and can affect a nursing infant. Besides, drinking a large amount may cause neural tube birth defect in babies. You can also read: Is green tea safe during pregnancy? 
  20. Nutrient absorption problem in children: The tannins in green tea may block nutrients absorption such as protein and fats in children. It may also lead to overstimulation because of the caffeine present in green tea.

Can people on a medication drink green tea? 

Green tea must not be taken along with these medications as it is known to cause negative reactions:

Highly Interactive

Stimulant drugs like Amphetamines, Nicotine, Cocaine and Ephedrine.

Moderately Interactive

Adenosine, Quinolone antibiotics, Birth control pills, Cimetidine (Tagamet), Clozapine (Clozaril), Dipyridamole (Persantine), Disulfiram (Antabuse), Estrogens pills, Fluvoxamine (Luvox), Lithium, Medications for depression (MAOIs), Hepatotoxic drugs, Medications that slow blood clotting (Anticoagulant / Antiplatelet drugs), Pentobarbital (Nembutal), Phenylpropanolamin, Riluzole (Rilutek), Theophylline, Verapamil and Warfarin.

Slightly Interactive

Alcohol, Fluconazole, Anti-diabetes drugs, Mexiletine (Mexitil) and Terbinafine.

How much green tea can you consume in a day?

The United Kingdom Tea Council recommends drinking not more than 6 cups of tea a day. For the best health benefits, 3 to 4 cups are recommended. However, doses of green tea vary significantly, but usually range between 1-5 cups daily is considered safe. The commonly used dose of green tea is based on the amount typically consumed in Asian countries, which is about 3 cups per day, providing 240-320 mg of the active ingredients, polyphenols. To make tea, people typically use 1 tsp of tea leaves in 8 ounces of boiling water.


You don’t have to quit drinking your favourite cup of green tea, but if you have any of the above mentioned medical conditions or taking prescription drugs, exercise caution and consult your doctor about how many cups you can have per day. Moderation is the key to enjoying the full benefits of green tea.

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