Does green tea have negative effects? What to know about risks and side effects

January 8, 2026 •

3 min read

Green tea is the second most consumed beverage globally, widely praised for its health-promoting antioxidants. However, many people wonder: does green tea have negative effects? While generally safe in moderation, excessive consumption or concentrated extracts can lead to notable health concerns for certain individuals.

Quick Summary

While generally safe in moderation, green tea can cause adverse effects for some due to its caffeine, tannins, and catechins. Potential issues include digestive problems, poor iron absorption, and interactions with medications, especially at high doses.

Key Points

Caffeine Sensitivity: Green tea's caffeine can cause insomnia, anxiety, and heart palpitations in sensitive individuals or at high doses.
Iron Absorption Interference: Tannins in green tea can inhibit the absorption of non-heme iron from plant-based foods, a concern for vegans and those with anemia.
Liver Damage from Extracts: High-dose green tea extract supplements have been linked to rare cases of liver toxicity and should be used with caution and medical supervision.
Digestive Issues: Drinking green tea on an empty stomach can trigger nausea and heartburn due to its tannin content increasing stomach acid.
Drug Interactions: Green tea can interact with medications, including blood thinners, stimulants, and beta-blockers, so consult a doctor if you are on medication.
Moderation is Key: For most healthy adults, 2–3 cups of brewed green tea per day is safe, but intake should be adjusted based on individual health factors.

Potential Side Effects of Green Tea

Green tea is known for its antioxidants, particularly catechins like epigallocatechin gallate (EGCG). However, these compounds can cause adverse reactions, especially in large amounts or as concentrated extracts. Understanding potential downsides is important for safe consumption.

Caffeine-Related Issues

Green tea contains caffeine, less than coffee, but enough to cause negative effects in caffeine-sensitive individuals. Caffeine levels vary by tea type and brewing time, with matcha being higher in caffeine than sencha. Concerns include:

Insomnia and Poor Sleep: Caffeine can disrupt sleep patterns by interfering with sleep-inducing chemicals.
Nervousness and Jitters: High caffeine intake can lead to anxiety, jitters, a rapid heartbeat, and restlessness.
Headaches: Caffeine can trigger or worsen headaches and migraines for some individuals.

Tannins and Digestive Discomfort

Green tea contains tannins, which give it an astringent taste and can affect digestion.

Stomach Upset and Nausea: Drinking green tea on an empty stomach can increase stomach acid, potentially causing nausea or heartburn, especially for those with sensitive digestion.
Constipation: Excessive tannins might sometimes lead to constipation.

Interference with Iron Absorption

Tannins in green tea can bind to non-heme iron from plant-based foods, inhibiting its absorption. This is particularly relevant for vegetarians, vegans, individuals with anemia, and pregnant women who are at higher risk of iron deficiency.

Tips to minimize this effect:

Consume green tea at least one to two hours away from iron-rich meals.
Pair iron-rich foods with Vitamin C, which enhances iron absorption.

The Serious Risks of Green Tea Extracts

While brewed green tea is generally safe, concentrated green tea extract (GTE) supplements pose higher risks, mainly to the liver. Rare but serious cases of liver damage and failure have been linked to high-dose GTE.

Hepatotoxicity: Concerns exist regarding high doses of EGCG, with intake over 800 mg per day not recommended by the European Food Safety Authority (EFSA).
Supplement vs. Brewed Tea: It's important to distinguish between moderate consumption of brewed green tea, which is not linked to liver damage, and high-dose supplements.

Drug Interactions

Green tea can interact with various medications due to its caffeine and other compounds. Consult a doctor if you are taking:

Blood Thinners: The Vitamin K in green tea can interfere with anticoagulants like warfarin.
Stimulant Drugs: Combining green tea's caffeine with other stimulants can cause excessive stimulation.
Beta-blockers: Green tea may reduce the absorption of certain beta-blockers, potentially decreasing effectiveness.

Comparison: Brewed Green Tea vs. Green Tea Extract Supplements


Feature	Brewed Green Tea (Moderate Intake)	Green Tea Extract Supplements (High Dose)
Preparation	Steeped leaves in water	Concentrated capsules or powders
Caffeine Level	Moderate (25-50 mg per cup)	Varies, potentially high and unregulated
Antioxidant Level	Moderate, absorbed over time	Very high, delivered in a concentrated dose
Liver Risk	Generally considered low	Potentially serious, linked to rare liver injury
Regulation	Regulated as a food product	Less regulated, can vary widely in potency
Targeted Use	Daily beverage for general health	Often for specific weight loss or antioxidant goals
Overall Safety	Safe for most in moderation	Requires caution and medical advice

Who Should Be Cautious with Green Tea?

Certain individuals should limit or avoid green tea:

Pregnant and Breastfeeding Women: Limit caffeine to less than 200mg daily. Catechins can interfere with folic acid absorption, important for fetal development.
Individuals with Anemia or Iron Deficiency: Due to tannins inhibiting iron absorption.
Caffeine-Sensitive Individuals: Consider decaffeinated options if experiencing anxiety or jitters.
Those with Liver Disease: Discuss consumption with a doctor and avoid concentrated supplements.
People with Glaucoma: Caffeine can increase eye pressure.
Individuals with Bleeding Disorders: Caffeine might increase bleeding risk.
Those on Certain Medications: Consult a healthcare professional about potential interactions.

Conclusion

While beneficial, green tea can have negative effects, especially when consumed excessively or as concentrated extracts. Risks stem from caffeine and tannins, potentially causing digestive issues, interfering with iron absorption, and leading to overstimulation. Green tea extracts are linked to rare liver damage. Moderation—a few cups of brewed tea daily—is key, along with awareness of individual health conditions and sensitivities. Consult a healthcare provider, especially if you have health concerns or take medication. More information on drug interactions is available on Drugs.com.

Frequently Asked Questions

Brewed green tea is generally not associated with liver damage. However, high doses of concentrated green tea extract (GTE) supplements have been linked to rare cases of liver injury and should be used with caution, ideally after consulting a healthcare provider.

Individuals with caffeine sensitivity, anemia, bleeding disorders, glaucoma, and liver disease should limit or avoid green tea. Pregnant and breastfeeding women, as well as those on certain medications, should also exercise caution and consult a doctor.

To prevent interference, avoid drinking green tea with meals or iron supplements. Experts recommend waiting at least one to two hours after eating before consuming green tea. Combining iron-rich meals with Vitamin C can also help.

For most healthy adults, 2–3 cups of brewed green tea per day is considered a safe and moderate intake. Drinking more than 8 cups daily is considered possibly unsafe due to high caffeine levels.

Small to moderate amounts (up to 2 cups per day) are considered possibly safe during pregnancy, but excessive intake is not recommended. High levels of caffeine and catechins can interfere with folic acid and fetal development.

Yes, green tea can interact with certain drugs, including blood thinners (like warfarin), stimulants, and some heart medications. It is essential to speak with a healthcare provider or pharmacist about potential interactions.

The tannins in green tea can increase stomach acid, which can cause nausea, heartburn, or an upset stomach when consumed on an empty stomach. It is best to drink it with or after a meal.

Even with less caffeine than coffee, green tea can cause side effects like insomnia, anxiety, jitters, and a rapid heartbeat in caffeine-sensitive individuals or when consumed in excess.