16 Side Effects Of Green Tea: Risks, Dosage & Precautions

Moderation in this drink can prevent nutrient loss, liver strain, and digestive upset.

By Medha deb

Created on Sep 18, 2025

Moderation in this drink can prevent nutrient loss, liver strain, and digestive upset.

Green tea is lauded for its health benefits — from aiding weight loss to reducing cardiovascular risks. However, it is crucial to recognize that excessive or inappropriate consumption of green tea can cause various adverse effects, ranging from mild discomfort to serious health hazards. This comprehensive guide covers the side effects, drug interactions, right dosage, and safety measures you need to know before making green tea a fixture in your diet.

Why Green Tea Has Side Effects
Short-Term Side Effects of Green Tea
Long-Term Side Effects of Green Tea
Green Tea Drug Interactions
Who Should Avoid Green Tea?
What Is the Right Dosage for Green Tea?
Precautions While Consuming Green Tea
When Should You See a Doctor?
Frequently Asked Questions (FAQs)

Why Green Tea Has Side Effects

While green tea is derived from the Camellia sinensis plant and is rich in beneficial compounds like catechins and epigallocatechin gallate (EGCG), it also contains biologically active substances including caffeine and tannins that can cause problems when consumed in excess. Some constituents may interfere with nutrient absorption, interact with medications, or overstimulate certain organs, leading to health complications.

Short-Term Side Effects of Green Tea

Short-term or acute side effects typically appear soon after drinking green tea, especially in higher quantities. Common issues include:

Headache – Excess caffeine can overstimulate the brain, causing headaches or migraines, especially in sensitive individuals.
Dizziness – Caffeine-induced changes in blood pressure and hydration levels may cause lightheadedness.
Nausea & Vomiting – Tannins may increase stomach acid, irritating the gut and causing nausea, vomiting, or even diarrhea. Symptoms worsen when green tea is taken on an empty stomach.
Anxiety, Nervousness & Restlessness – The caffeine content can cause jitters, restlessness, and an inability to relax, particularly in those sensitive to stimulants.
Heartburn or Acid Reflux – Green tea may raise stomach acid, triggering heartburn, bloating, or reflux in susceptible people.
Stomach Pain – Direct irritation of the stomach lining can lead to discomfort, abdominal cramps, or even exacerbation of ulcers.
Frequent Urination – Caffeine acts as a diuretic, increasing urination frequency and potentially leading to dehydration if not counterbalanced by water intake.

Side Effect	Possible Cause	Who is Most at Risk?
Headache / Dizziness	Caffeine Overload	People sensitive to caffeine
Nausea, Vomiting	Tannins; Empty Stomach	People with digestives issues
Anxiety, Restlessness	Stimulant in caffeine	Anxiety-prone individuals
Heartburn	Increased stomach acid	People prone to acid reflux

Long-Term Side Effects of Green Tea

Chronic overuse or sensitive underlying health can predispose certain individuals to significant long-term effects, such as:

Anemia or Iron Deficiency – Catechins in green tea hinder iron absorption, leading to a decrease in hemoglobin and red blood cell count after prolonged use. This may result in fatigue, paleness, and overall weakness.
Bone Weakness – Chronic caffeine intake may elevate calcium excretion via urine, weakening the bones and increasing the risk of fractures, especially in those with osteoporosis.
Hepatotoxicity (Liver Injury) – Overconsumption, particularly of concentrated green tea extracts, has been associated with cases of liver damage in some individuals. Monitoring of liver function is recommended for long-term/high-dose users.
Impaired Thyroid Function – High amounts of green tea caffeine (notably during pregnancy) can negatively affect thyroid hormone production, causing metabolic disturbances. Research indicates increased thyroid cancer risk in premenopausal women, but some protection in postmenopausal women.
Seizures – In rare cases, excessive caffeine intake may increase the risk of seizures.
Increased Risk of Birth Defects – Pregnant women consuming high doses risk passing excessive caffeine to the fetus, which may contribute to low birth weight or congenital abnormalities.

Summary Table: Long-Term Risks

Risk	Causing Agent	Populations Most Affected
Anemia	Catechins	Women, vegetarians, children
Bone Loss	Caffeine/Calcium Loss	Older adults, menopausal women
Liver Toxicity	High-dose extracts	Supplement users
Birth Defects	Caffeine	Pregnant women, fetuses

Green Tea Drug Interactions

Caffeine and active compounds in green tea can interact with various medications, sometimes reducing efficacy or increasing side effects:

Antibiotics – Can intensify caffeine effects, triggering jitteriness and rapid heartbeat.
Anticoagulants (Blood Thinners) – May reduce efficacy and increase bleeding risk due to vitamin K in green tea.
Antidepressants – Some can increase caffeine’s stimulatory effects, causing nervousness or insomnia.
Birth Control Pills – May prolong caffeine’s action in the body, intensifying side effects.
Anesthetics – Risk of amplified cardiovascular effects if consumed before surgery.

Always inform your healthcare provider about your green tea intake if you are prescribed medication.

Who Should Avoid Green Tea?

Certain individuals should limit or completely avoid green tea due to increased risk of adverse effects:

Pregnant and breastfeeding women – High caffeine levels can harm fetal/infant health.
People with stomach sensitivity or ulcers – Tannins may worsen stomach issues.
Children – Caffeine may disturb development and nutrient absorption.
People with anxiety disorders – Caffeine can exacerbate symptoms.
Individuals with heart arrhythmias – Stimulants may increase risk of palpitations.
Those with osteoporosis – Potential for increased calcium loss.
Patients with liver disease – Caution with high-dose or concentrated green tea supplements.
People on blood thinners or other interaction-prone medications.
People with glaucoma – Caffeine may raise intraocular pressure.

What Is the Right Dosage for Green Tea?

Moderation is key to safely enjoying green tea’s potential health benefits while minimizing risks. The widely recommended dosage is:

2 to 3 cups per day for most healthy adults.
Aim for total caffeine intake from all sources to remain below 300 mg daily.
Pregnant and breastfeeding women are advised to further lower caffeine intake.

This equates to roughly 250-300 mg of catechins and 100-150 mg of EGCG daily. Exceeding these amounts may increase the likelihood of side effects.

Precautions While Consuming Green Tea

Do not drink green tea on an empty stomach — as this increases gastric irritation and nausea.
Avoid green tea late in the day or at night — to prevent sleep disturbances.
If you experience unusual symptoms (such as palpitations, cramps, dizziness), discontinue use and seek medical advice.
If you have chronic illness or take medication, consult your physician before regular green tea intake.
Limit green tea extract supplements; these carry a higher risk of liver toxicity than brewed tea.
Balance with iron-rich foods or consume green tea between meals rather than during meals to reduce the risk of iron deficiency.

When Should You See a Doctor?

Contact your healthcare provider immediately if you notice:

Persistent muscle twitches or cramps
Abnormal heart rhythms or palpitations
Unusually high frequency of dizziness or nausea
Noticeable increase in bone injuries or unexplained inflammation
Signs of allergy (hives, swelling, shortness of breath)

These may indicate severe reactions or underlying health issues aggravated by green tea consumption.

Infographic: 6 Negative Effects Of Overconsumption Of Green Tea

Iron deficiency/anemia
Drug interactions
Seizures
Headache and dizziness
Bone weakness
Anxiety, heartburn, frequent urination

Always consume green tea in moderation and avoid it entirely if you fall under high-risk groups without professional guidance.

Frequently Asked Questions (FAQs)

Q: Does green tea have any side effects for skin or hair?

There is currently no scientific evidence indicating that green tea has adverse effects on skin or hair. However, if you notice any negative reactions, discontinue use and consult your doctor.

Q: What is the correct time to drink green tea?

You may drink green tea at any time, but the best times are early morning or afternoon to enhance metabolism, focus, and exercise results. Avoid bedtime consumption due to caffeine content.

Q: Can green tea cause allergies?

Though rare, green tea can trigger serious allergies like anaphylaxis. Watch for sudden breathing difficulty, vomiting, or shocking symptoms and seek immediate medical help if they occur.

Q: Can I drink green tea at night?

It depends on individual sensitivity. Many people experience sleep disturbances from the caffeine in green tea when consumed late in the evening or at night.

Q: Is there a difference between loose leaf green tea and tea bags?

Loose leaf tea uses whole leaves requiring measurement and longer steeping, whereas tea bags often use tea fragments or dust for quick brewing and convenience.

Key Takeaway

Green tea, though loaded with antioxidants like EGCG and other beneficial compounds, is not risk-free. Moderation (2–3 cups daily) is vital. People with preexisting health conditions, pregnant women, children, and those on certain medications should exercise caution or avoid green tea altogether. Consult a healthcare professional to make informed dietary choices and minimize risks.

References

Author

medha deb

Medha Deb is an editor with a master's degree in Applied Linguistics from the University of Hyderabad. She believes that her qualification has helped her develop a deep understanding of language and its application in various contexts.

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