Does Green Tea Have Negative Side Effects?

December 1, 2025 •

3 min read

While green tea is often praised for its health benefits, excessive consumption can lead to notable side effects due to its caffeine and tannin content. The key to enjoying this popular beverage safely is understanding the potential downsides and practicing moderation.

Quick Summary

This article explores the potential negative side effects of green tea, including digestive issues, caffeine-related anxiety, and medication interactions, emphasizing that risks are often tied to excessive intake or individual sensitivity.

Key Points

Caffeine Sensitivity: High intake can cause anxiety, jitteriness, and insomnia in those sensitive to caffeine.
Digestive Issues: Tannins can irritate the stomach, causing nausea, acid reflux, or diarrhea, especially when consumed on an empty stomach.
Iron Absorption: Catechins can inhibit the absorption of non-heme iron, an important consideration for individuals with anemia or iron deficiency.
Liver Health: High-dose green tea extracts, unlike brewed tea, have been linked to rare cases of liver damage.
Medication Interference: Green tea can negatively interact with medications such as blood thinners, certain psychiatric drugs, and blood pressure medication.
Moderation is Essential: The vast majority of negative effects are tied to excessive intake, and moderate consumption is generally considered safe for most people.

Exploring the Compounds in Green Tea

Green tea, derived from the Camellia sinensis plant, is rich in powerful antioxidants called catechins, especially epigallocatechin gallate (EGCG). It also contains caffeine, though typically in lower amounts than coffee, and tannins. These compounds, while beneficial in moderate doses, can be the source of negative effects if consumed excessively or by sensitive individuals.

Common Side Effects from Overconsumption

Most negative effects from green tea are linked to consuming large quantities, often more than 8 cups per day, or taking concentrated extracts.

Caffeine-Related Issues

Green tea’s caffeine content can cause problems for sensitive individuals or when intake is high. Common symptoms include:

Anxiety and Jitteriness: Caffeine stimulates the nervous system, potentially causing restlessness and irritability.
Insomnia: Drinking green tea late in the day can disrupt sleep patterns.
Increased Heart Rate and Blood Pressure: High caffeine intake can cause an irregular or rapid heartbeat, especially for those with existing heart conditions.
Headaches: Frequent caffeine intake or withdrawal can trigger headaches or migraines in susceptible people.

Digestive Problems

The tannins in green tea can affect the digestive system, particularly when consumed on an empty stomach.

Stomach Irritation and Nausea: Tannins can increase stomach acid, leading to irritation, acid reflux, or nausea.
Diarrhea or Constipation: Caffeine can act as a laxative, leading to diarrhea, while the tannins may cause constipation.
Recommendation: To minimize digestive upset, it is best to drink green tea with or after a meal rather than on an empty stomach.

Nutrient Absorption Interference

Iron Deficiency Anemia: The catechins and tannins in green tea can hinder the absorption of non-heme iron (found in plant-based foods). This is a particular concern for individuals already at risk, such as those with anemia, pregnant women, or vegetarians. Drinking green tea away from meals and adding lemon (vitamin C) can help counteract this effect.

Risks Associated with Green Tea Extracts

While brewed green tea is generally safe, concentrated green tea extracts found in supplements carry higher risks, including potential liver damage. The European Food Safety Authority (EFSA) suggests caution with doses of epigallocatechin gallate (EGCG) exceeding 800 mg per day from supplements.

Green Tea's Impact on Specific Health Conditions and Medications

Certain individuals and those on specific medications should be cautious with their green tea intake due to potential complications.

Comparative Overview of Green Tea and Potential Risks


Potential Side Effect	Cause	Risk Level with Moderate Intake (2-4 cups/day)	Risk Level with Excessive Intake	Who is at Highest Risk?
Anxiety/Insomnia	Caffeine	Low to Moderate (if sensitive)	High	Caffeine-sensitive individuals, those with anxiety disorders.
Stomach Upset	Tannins and Caffeine	Low (especially if consumed with food)	High	Individuals with sensitive stomachs, IBS, or acid reflux.
Reduced Iron Absorption	Tannins and Catechins	Low (if consumed away from meals)	Moderate to High	Anemic individuals, pregnant women, vegetarians.
Liver Damage	EGCG (specifically concentrated supplements)	Very Low	High	Anyone taking high-dose green tea extract supplements.
Medication Interactions	Caffeine, Catechins, Vitamin K	Varies depending on medication	High	People on blood thinners, stimulants, or certain psychiatric medications.

Medication Interactions

Green tea can interact with a number of medications, potentially altering their effectiveness or increasing side effects. Interactions may occur with:

Blood Thinners (e.g., Warfarin): Green tea contains small amounts of vitamin K, which can interfere with blood clotting. Large, consistent amounts should be avoided.
Stimulants (e.g., ADHD medications): Combining green tea's caffeine with other stimulants can overstimulate the nervous system, increasing heart rate and blood pressure.
Certain Psychiatric Drugs (e.g., Clozapine): Green tea's caffeine can compete with some medications for liver metabolism, potentially increasing drug levels and side effects.
Some Blood Pressure and Cholesterol Meds: Green tea can affect the absorption of certain drugs like nadolol and atorvastatin.

Conclusion: Moderation is Key

While green tea offers numerous health benefits, it's not without potential downsides. Most negative side effects are associated with excessive consumption, high-dose extracts, or specific individual sensitivities. People who are sensitive to caffeine, have pre-existing conditions like anemia or IBS, or take specific medications should be particularly mindful of their intake. For most healthy adults, enjoying green tea in moderation (around 2–3 cups a day) is considered safe and beneficial. Being aware of these risks and listening to your body can ensure you enjoy green tea as a healthful part of your routine. Always consult a healthcare professional with specific health concerns, especially concerning medication interactions.

Authoritative Source

For comprehensive medical information on green tea's effects and interactions, please visit the WebMD Green Tea page.

Frequently Asked Questions

Excessive green tea consumption is generally considered to be more than 8 cups per day for most healthy adults, with risks increasing significantly at higher doses or with concentrated extracts.

While regular brewed green tea is unlikely to cause liver issues, high-dose green tea extract supplements have been linked to rare cases of liver damage. It's best to consult a doctor before taking green tea supplements.

Yes, drinking green tea on an empty stomach can cause stomach irritation, nausea, and acid reflux due to its tannin content, especially for those with sensitive digestive systems.

Yes, green tea can interfere with several medications, including blood thinners like warfarin, stimulant drugs, certain psychiatric medications, and some blood pressure drugs.

In large quantities, green tea can inhibit the absorption of non-heme iron from plant-based foods due to its tannins and catechins. This is a concern for people with existing iron deficiency or anemia.

Certain groups should avoid or limit green tea intake, including pregnant or breastfeeding women, those with severe caffeine sensitivity, individuals with anemia, and people with liver or bleeding disorders.

While moderate, regular consumption may help lower blood pressure for some, high doses of caffeine can temporarily increase heart rate and blood pressure, which is a concern for people with heart conditions.