7 harmful side effects of excessive consumption of green tea

Research and blogs talk a lot about the health benefits of green tea. It’s rich in antioxidants and flavonoids, which have positive influences on our physical and mental well-being.

Some studies show that green tea can boost metabolism, reduce inflammation, and improve cognitive function. 

Green tea, often hailed as a miraculous elixir, has woven its way into the fabric of health and wellness cultures worldwide. Its origins trace back to ancient China, where it was prized for its medicinal properties.

Today, green tea is celebrated for its abundant antioxidants, with many enthusiasts embracing it for its potential to boost weight loss, improve brain function, and reduce the risk of heart disease. However, despite its widespread acclaim, green tea has drawbacks.

In this blog, we delve into the lesser-known side of green tea – its side effects. While it’s lauded for its health benefits, it’s crucial to acknowledge that even natural products like green tea can have adverse effects, especially when consumed in large quantities.

Did you know facts about green tea?

Green tea, a beverage steeped in both history and health, has been a staple in various cultures for centuries. Originating in China around 2737 BC, it quickly spread throughout Asia and eventually gained popularity worldwide. 

Unlike black or oolong teas, green tea is made from unoxidized leaves and is the least processed form, allowing it to retain most of its natural antioxidants and polyphenols.

The key to green tea’s benefits lies in its rich composition of catechins, particularly epigallocatechin gallate (EGCG), which is known for its potent antioxidant properties.

These antioxidants neutralize harmful free radicals in the body, contributing to reduced inflammation and potentially lower risks of certain diseases. 

Green tea is also known for containing amino acids like L-theanine, which, when combined with caffeine, can enhance brain function, improve mood, and increase alertness without the jitteriness often associated with coffee.

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What is the main benefit of green tea?

Green tea, a cherished staple in many cultures, is celebrated for its array of health benefits [1]. This natural beverage, rich in antioxidants, offers a multitude of positive effects, ranging from improved brain function to potential cancer prevention.

  • Rich in antioxidants: Green tea is loaded with powerful antioxidants, particularly catechins like epigallocatechin gallate (EGCG). These antioxidants help neutralize harmful free radicals, reduce oxidative stress, and potentially lower the risk of chronic diseases.
  • Enhances brain function: The moderate caffeine content in green tea acts as a stimulant to improve brain function, including enhanced mood, vigilance, reaction time, and memory. Additionally, it contains the amino acid L-theanine, which can work synergistically with caffeine to improve brain function.
  • Supports heart health: Regular consumption of green tea has been linked to a reduced risk of heart disease. It helps in lowering LDL cholesterol levels and improving the overall cholesterol profile, thereby reducing the risk of heart strokes and heart attacks.
  • Aids in weight loss: Green tea has been shown to boost the metabolic rate in the short term, making it a popular beverage for weight loss and weight management.
  • May lower cancer risk: The antioxidants in green tea may help in reducing the risk of various types of cancer, including breast, prostate, and colorectal cancer [2].
  • Supports dental health: Catechins in green tea also have biological effects. Some studies show that they can kill bacteria and inhibit viruses like the influenza virus, potentially lowering your risk of infections and improving dental health.
What is the main benefit of green tea?

What are the adverse effects of green tea?

Side effects are more limited when consuming green tea versus other beverages that contain caffeine since green tea contains less caffeine and has a shorter brewing time.

However, increased caffeine sensitivity or certain prescriptions can lead to some adverse reactions when consuming green tea.

1. Symptoms of anxiety

This is primarily attributed to its caffeine content. While green tea contains less caffeine than coffee, sensitive individuals may still experience anxiety symptoms [3].

These can include increased heart rate, restlessness, feelings of nervousness, and even panic attacks in extreme cases. 

The stimulating effects of caffeine can activate the body’s ‘fight or flight’ response [4], leading to heightened anxiety levels.

It’s important for those prone to anxiety or caffeine sensitivity to monitor their green tea intake or opt for decaffeinated varieties to mitigate these effects.

2. Insomnia

Again, if you’re sensitive to caffeine, consuming large amounts of green tea may lead to sleep issues.

Bioactive compounds in green tea prevent your body from releasing hormones such as melatonin, which trigger your body to wind down and ready itself for sleep.

If you have difficulty sleeping or suffer from sleep disorders, you should avoid consuming more than a few cups of green tea a day [5].

This is especially true for matcha, which has a higher concentration of caffeine than plain brewed green tea. 

3. Teeth stains

While green tea is celebrated for its health benefits, it can have an unexpected drawback: teeth staining.

The tea contains tannins, natural compounds that contribute to its flavor and color [6]. These tannins can adhere to dental enamel, leading to discoloration over time.

This staining is similar to what occurs with other tannin-rich beverages like coffee and red wine. 

The degree of staining depends on the consumption frequency and individual dental hygiene practices.

Regular dental cleanings and good oral hygiene can help mitigate this effect [7], but avid green tea drinkers should be aware of this potential impact on their smile.

4. Liver conditions

The European Food Safety Authority previously assessed the effects of the catechins in green tea on the human body, particularly the liver.

Some reports emerged from Nordic countries that associated the use of green tea products with initial symptoms of liver damage.

Green tea infusions (such as brewed tea) contain safe levels of epigallocatechin 3-gallate (EGCG), which is a catechin found in tea leaves.

However, green tea extracts and supplements may contain at least 800mg per dose, which has associations with symptoms of negative effects on the liver. Further studies are required to validate, but the risk is present [8].

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5. Drug interactions

Persons who take certain prescriptions, such as nadolol or polypeptide antibiotics, should be mindful when consuming green tea due to potential negative interactions.

The catechins in green tea may inhibit the uptake of nadolol in the digestive system and significantly reduce its effects on systolic blood pressure [9].

Meanwhile, for patients taking substrates of polypeptides, such as antibiotics, you should exercise caution when consuming green tea.

EGCG may potentially inhibit the effects of quetiapine, sunitinib, and clozapine; meanwhile, it may increase the effects of diltiazem, verapamil, and nicardipine [10].

6. Stomach irritation

If you consume strong brews of green tea or consume it on an empty stomach, the beverage may cause stomach irritation.

Tannins increase the acid in your stomach, which can lead to digestive conditions such as acid reflux or nausea. Caffeine also has a laxative effect, which may lead to diarrhea [11].

The EGCG polyphenol may also cause gastrointestinal toxicity when consumed in high doses, though this is mostly due to the consumption of concentrated green tea extract [12].

7. Anaemia and other deficiencies in iron

While green tea is celebrated for its health benefits, it can adversely affect iron absorption, leading to anemia and other iron deficiencies.

The tannins present in green tea bind to iron, especially the non-heme iron found in plant-based foods, reducing its absorption in the body. 

This effect is particularly concerning for individuals with existing iron deficiency or those prone to anemia. Consuming green tea along with iron-rich meals may exacerbate this issue.

It’s essential for those at risk of iron deficiency to monitor their green tea intake and consult healthcare professionals for dietary advice.

Anaemia and other deficiencies in iron

What happens if I drink green tea everyday?

There’s no denying green tea’s benefits on your health – it’s rich in antioxidants and anti-inflammatory compounds, which positively influence your well-being and longevity.

But as with many foods and drinks, you must consume green tea in moderation so that you don’t trigger any of its potential side effects.

This is especially important to consider if you have a sensitivity to caffeine, suffer from iron deficiency, or take certain prescriptions.

People with hypertension should also be cautious when consuming green tea since the caffeine elevates their heart rate.

But so long as you keep it within 2–5 cups – or less than a liter – per day, and follow proper brewing instructions, green tea is a wise and healthy addition to any diet!

Final takeaways

Green tea, though widely acclaimed for its health benefits, is not without its drawbacks. From inducing symptoms of anxiety to causing insomnia, staining teeth, impacting liver health, interacting with drugs, causing stomach issues, and contributing to anemia and iron deficiencies, it’s clear that moderation is key. 

These side effects underscore the importance of consuming green tea with a mindful approach, especially for individuals with pre-existing conditions or those on certain medications.

While green tea can be a beneficial addition to many diets, it’s not a one-size-fits-all solution.

Paying attention to your body’s reactions and consulting with a healthcare professional can help mitigate any adverse effects.


Is green tea safe to take?

Green tea is safe for most people when consumed in moderation; however, it’s advisable to consult with a healthcare provider if you have any existing health conditions or are on medication.

What are the negative effects of green tea?

Excessive consumption of green tea can lead to side effects such as insomnia, anxiety, digestive issues, liver problems, and iron deficiency.

What happens if I drink green tea every day?

Drinking green tea daily in moderation is generally safe, but excessive intake can cause caffeine-related side effects, iron absorption issues, and potential liver damage.

Can green tea cause liver problems?

While rare, excessive consumption of green tea, especially in supplement form, can lead to liver problems, including liver toxicity.

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[1] https://www.miragenews.com/tea-culture-health-benefits-of-worlds-favorite-992762/
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7059963/
[3] https://www.everydayhealth.com/diet-nutrition/diet/reasons-youre-sensitive-caffeine-what-have-instead/
[4] https://psychcentral.com/blog/caffeines-effects-on-your-thinking
[5] https://pubmed.ncbi.nlm.nih.gov/14592218/
[6] https://tecompanytea.com/blogs/tea-atelier/what-are-tannins-in-tea
[7] https://my.clevelandclinic.org/health/treatments/11187-dental-check-up
[8] https://www.efsa.europa.eu/en/press/news/180418
[9] https://pubmed.ncbi.nlm.nih.gov/24419562/
[10] https://pubmed.ncbi.nlm.nih.gov/28118673/
[11] https://senchateabar.com/blogs/blog/green-tea-side-effects
[12] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1964900/

Photograph: koko rahmadie/Pexels
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