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Short answer: For most adults, green tea as a drink is safe. The U.S. National Center for Complementary and Integrative Health says no safety concerns have been reported for green tea consumed as a beverage by adults. Most side effects people notice, such as nausea, headaches, jitters, trouble sleeping and peeing more, come from its caffeine or from drinking it on an empty stomach. Liver problems are rare and have mainly been linked to concentrated green tea extract pills, not brewed tea. An 8-ounce cup of brewed green tea has about 29 mg of caffeine, less than a third of the amount in the same size cup of brewed coffee.
Green tea has a reputation as one of the gentlest drinks around, so it can be confusing when a cup leaves you queasy, dizzy or running to the bathroom. Here is what causes the most common green tea side effects, how much is too much, how brewed tea differs from green tea extract supplements, and who should be more careful.
What you'll learn
- Whether green tea is bad for you, and what the safety research says
- Why green tea can make you nauseous, pee more, get a headache, feel dizzy or sleepy
- How green tea affects iron absorption
- What is known about green tea, extracts and the liver
- How much green tea is too much, and who should be careful
Is green tea bad for you?
Not for most people. "No safety concerns have been reported for green tea consumed as a beverage by adults," according to the National Center for Complementary and Integrative Health, which adds that green tea does contain caffeine (NCCIH). The European Food Safety Authority reached a similar view: catechins from green tea brewed in the traditional way are generally considered safe at the amounts people usually drink (EFSA, 2018).
The side effects people search for tend to fall into three groups: effects of caffeine, stomach upset, and, rarely, problems linked to concentrated green tea extracts. The table below sums them up.
| Side effect | Most likely reason | What to try |
|---|---|---|
| Nausea or upset stomach | Caffeine increases stomach acid (MedlinePlus); nausea is a listed effect of too much caffeine (FDA) | Drink it with or after food, or make it weaker |
| Peeing more | Caffeine is a diuretic, and tea is mostly water (MedlinePlus) | Usually harmless; spread cups out if it bothers you |
| Headache or dizziness | Too much caffeine, or caffeine withdrawal when you cut back (MedlinePlus) | Count your total caffeine; cut back gradually |
| Jitters, fast heartbeat, anxiety | Too much caffeine (FDA) | Fewer cups, or switch some to decaf green tea |
| Trouble sleeping | Caffeine late in the day (Gardiner et al., 2023) | Have your last cup earlier |
| Lower iron absorption | Tea polyphenols bind non-heme iron in a meal (Hurrell et al., 1999) | Drink tea between meals if your iron is low |
| Liver problems (rare) | Mainly concentrated extract pills (NCCIH) | Stop and see a doctor if you notice warning signs |
Why does green tea make me nauseous?
The most likely reason is caffeine. Caffeine increases the release of acid in your stomach, which sometimes leads to an upset stomach or heartburn (MedlinePlus), and the FDA lists upset stomach and nausea among the effects of too much caffeine (FDA).
For green tea extract supplements, there is specific advice: a United States Pharmacopeia expert panel recommends a label warning not to take powdered green tea extract on an empty stomach and to take it with food, because taking it while fasting raises how much of its main catechin, EGCG, reaches the blood (Oketch-Rabah et al., 2020). Nausea, constipation and abdominal discomfort are also reported side effects of green tea extract supplements (NCCIH).
If brewed green tea upsets your stomach, try it with a meal or snack, use less tea or a shorter steep for a milder cup, and see our guide on how to brew green tea. If you have GERD or ulcers, check with your health care provider about caffeine (MedlinePlus).
Why does green tea make me pee so much?
Two reasons: a cup of tea is mostly water, and caffeine is a diuretic, meaning it helps your body get rid of extra salt and water by urinating more (MedlinePlus). Brewed green tea is 99.9% water (USDA FoodData Central).
For regular tea drinkers, this usually does not lead to dehydration. A review of the research found that caffeine noticeably raises urine output mainly when people take a large dose, at least 250 to 300 mg at once, after going without caffeine; regular coffee and tea drinkers develop a strong tolerance to this effect (Maughan & Griffin, 2003). In a small trial in 21 men, four to six mugs of black tea a day kept them as hydrated as the same amount of water (Ruxton & Hart, 2011). For more on caffeinated drinks and hydration, see does coffee count toward your water intake.
Can green tea give you a headache or make you dizzy?
Yes, usually because of caffeine. Too much caffeine can cause headaches, dizziness, restlessness, shakiness, insomnia, a fast heart rate and anxiety (MedlinePlus). Caffeine can also cause headaches the other way around: if you consume it regularly and suddenly stop, withdrawal symptoms can include headaches, drowsiness, irritability, nausea and trouble concentrating, and usually go away after a couple of days (MedlinePlus).
Green tea alone rarely adds up to a lot of caffeine, but it adds to what you get from coffee, soda, energy drinks and pre-workout products. If you have migraines or other chronic headaches, check with your health care provider about whether to limit caffeine (MedlinePlus). Dizziness with chest pain, fainting or a racing heartbeat needs medical attention.
Why does green tea make me sleepy?
There is little research on this question directly. One common explanation is a drop in caffeine: an 8-ounce cup of brewed green tea has about 29 mg of caffeine, compared with about 95 mg in the same amount of brewed coffee (USDA FoodData Central; USDA FoodData Central). If you swap coffee for green tea, you may be getting much less caffeine than usual, and drowsiness is one of the symptoms of caffeine withdrawal (MedlinePlus).
For most people, the bigger risk runs the other way. In a meta-analysis of 24 studies, caffeine reduced total sleep time by 45 minutes and sleep efficiency by 7%, and the authors suggested having a cup of coffee at least 8.8 hours before bed to avoid losing sleep (Gardiner et al., 2023). Green tea has less caffeine than coffee, but a late cup can still affect your sleep if you are sensitive. See how much caffeine is in tea.
Green tea and iron absorption
Tea can reduce how much iron you absorb from plant foods and fortified foods (non-heme iron) eaten at the same meal. In a classic study, black tea served with a bread meal cut iron absorption by 79% to 94% compared with water, and adding milk made little or no difference (Hurrell et al., 1999). That study tested black tea, not green tea, but reviews list tea in general among the foods and drinks that inhibit iron absorption (Zijp et al., 2000).
For most people eating a varied diet, this matters little. A review by researchers at a tea company concluded that enough vitamin C, meat, fish or poultry in a meal can largely overcome the effect of tea, but that iron absorption may be an issue for people with low iron stores who eat little meat (Zijp et al., 2000). If you have low iron, are vegetarian or vegan, or have been told you are anemic, drink green tea between meals rather than with them, and ask your health care provider about your iron.
Green tea, green tea extract and your liver
Liver injury is uncommon, and it has been reported mainly in people who used green tea extracts in tablet or capsule form; people with a specific variant of an immune system gene appear to be especially susceptible (NCCIH).
| Brewed green tea | Green tea extract supplements | |
|---|---|---|
| Typical EGCG a day | 90 to 300 mg on average for green tea drinkers, up to about 866 mg in high consumers (EFSA, 2018) | 5 to 1,000 mg a day, depending on the product (EFSA, 2018) |
| What reviews found | Generally considered safe when brewed in the traditional way; rare, unpredictable liver cases have been reported (EFSA, 2018) | 800 mg of EGCG a day or more raised liver enzymes in clinical trials (EFSA, 2018) |
| How it is taken | Spread out as a drink, usually with food | Concentrated doses, sometimes on an empty stomach, which raises EGCG in the blood (Oketch-Rabah et al., 2020) |
A systematic review of 159 human studies, written by scientists at a supplement company, found that liver side effects were linked to large, concentrated doses taken at once, not to brewed tea or extracts taken in drinks or food (Hu et al., 2018). The USP panel noted case reports of liver injury at EGCG intakes from 140 mg to about 1,000 mg a day, with large differences in how sensitive people were (Oketch-Rabah et al., 2020).
If you take a green tea extract supplement, take it with food, and do not use it if you have a liver problem. Stop and contact a health care provider if you notice signs of liver trouble such as abdominal pain, dark urine, or yellowing of the skin or eyes (Oketch-Rabah et al., 2020).
Green tea and medications
Green tea can interact with some medicines. At high doses, green tea has been shown to lower blood levels of the blood pressure drug nadolol, and green tea extract can lower blood levels of the cholesterol drug atorvastatin; it may also interact with other medicines (NCCIH). Its caffeine can interact too, including with stimulants, certain antibiotics, asthma medicines and heart medicines (MedlinePlus).
If you take any prescription medicine, ask your doctor or pharmacist whether green tea or green tea extract is a problem for you, and how to time it. Do not stop or change a medicine on your own.
How much green tea is too much?
For most healthy adults, caffeine is what sets the limit. The FDA cites 400 mg of caffeine a day as an amount not generally associated with negative effects (FDA).
| Drink | Caffeine |
|---|---|
| Brewed green tea, 8 oz | About 29 mg (USDA FoodData Central) |
| Brewed green tea, 12 oz | About 37 mg (FDA) |
| Decaf green tea, 8 oz | 0 mg listed (USDA FoodData Central) |
| Brewed coffee, 8 oz, for comparison | About 95 mg (USDA FoodData Central) |
| 400 mg a day in 8-oz cups of green tea, by our calculation | About 13 cups |
That does not mean 13 cups a day is a goal. Caffeine from coffee, soda and other drinks counts toward the same total, matcha has more caffeine than brewed green tea (see is matcha bad for you), and some people feel side effects at much lower amounts. Signs that you have had too much include jitters, a fast or pounding heartbeat, anxiety, an upset stomach, headache and trouble sleeping (FDA).
Who should be careful with green tea
- Pregnant or breastfeeding. Caffeine passes to the baby (MedlinePlus). Ask your health care provider how much caffeine is right for you.
- People sensitive to caffeine, or with sleep problems, anxiety, migraines, GERD or ulcers, heart rhythm problems or high blood pressure (MedlinePlus).
- People who take medicines, including nadolol and atorvastatin (NCCIH), or stimulants, certain antibiotics, asthma or heart medicines (MedlinePlus).
- People with low iron or who eat little meat (Zijp et al., 2000).
- Anyone with a liver condition considering green tea extract supplements (Oketch-Rabah et al., 2020).
- Children and teens, who should have less caffeine than adults (MedlinePlus).
How to enjoy green tea with fewer side effects
- Have it with food if it upsets your stomach.
- Keep it earlier in the day if caffeine affects your sleep (Gardiner et al., 2023).
- Count all your caffeine, not just tea, and stay within about 400 mg a day if you are a healthy adult (FDA).
- Cut back slowly to avoid withdrawal headaches (MedlinePlus).
- Drink tea between meals if you need to protect your iron (Hurrell et al., 1999).
- Choose the drink over pills. No safety concerns have been reported for green tea as a drink in adults; the rare liver cases have mainly involved concentrated extracts (NCCIH).
- Curious about matcha? It has more caffeine than brewed green tea. See matcha vs green tea.
Common myths (quick reality check)
Myth: Green tea has no side effects because it is natural. Reality: Green tea contains caffeine, which can cause nausea, headaches, jitters and poor sleep in some people.
Myth: Green tea is bad for your liver. Reality: Liver injury is uncommon and has mainly been linked to concentrated extract pills, not brewed tea.
Myth: Green tea dehydrates you. Reality: Tea is mostly water, and regular tea drinkers develop tolerance to caffeine's mild diuretic effect.
Frequently asked questions (FAQ)
What are the side effects of drinking too much green tea?
Mostly caffeine effects: jitters, fast heartbeat, anxiety, upset stomach, nausea, headache and trouble sleeping. Tea with meals can also reduce iron absorption.
Why does green tea make me nauseous?
Caffeine increases stomach acid, which can upset your stomach. Drinking it with food or making it weaker often helps.
Why does green tea make me pee so much?
Tea is mostly water, and caffeine is a mild diuretic. In regular tea drinkers this does not usually cause dehydration.
Why does green tea make me dizzy?
Too much caffeine can cause dizziness and a fast heart rate. Dizziness with chest pain or fainting needs medical attention.
How many cups of green tea a day is safe?
For most healthy adults, caffeine sets the limit. At about 29 mg per 8-ounce cup, 400 mg would be about 13 cups by our calculation, counting no other caffeine.
Is green tea bad for your liver?
Brewed green tea is generally considered safe. Rare liver injury has mainly been linked to concentrated green tea extract supplements.
Can I drink green tea on an empty stomach?
Many people can, but caffeine increases stomach acid. If it makes you queasy, have it with food. Green tea extract supplements should be taken with food.
Related guides
- Is matcha bad for you? Side effects and how much is safe
- How much caffeine is in tea?
- Matcha vs green tea
- How to brew green tea
- L-theanine side effects
- How much caffeine is too much?
Disclaimer and when to seek help
This article is for general education and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Our products are not intended to diagnose, treat, cure, or prevent any disease. Talk to your health care provider if you are pregnant or breastfeeding, have a heart, liver or stomach condition, have low iron, or take medication. Get medical help right away for chest pain, fainting, a racing or irregular heartbeat, or signs of liver trouble such as dark urine or yellowing of the skin or eyes.
References
- National Center for Complementary and Integrative Health. "Green Tea: Usefulness and Safety". Updated February 2025.
- U.S. Food and Drug Administration. "Spilling the Beans: How Much Caffeine Is Too Much?" Content current as of August 28, 2024.
- MedlinePlus (U.S. National Library of Medicine). "Caffeine". Last updated September 8, 2021.
- U.S. Department of Agriculture. FoodData Central, SR Legacy 171917: Beverages, tea, green, brewed, regular; 171910: Beverages, tea, green, brewed, decaffeinated; 171890: Beverages, coffee, brewed.
- EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS). "Scientific opinion on the safety of green tea catechins." EFSA Journal, 2018;16(4):e05239. doi:10.2903/j.efsa.2018.5239
- Oketch-Rabah HA, et al. "United States Pharmacopeia (USP) comprehensive review of the hepatotoxicity of green tea extracts." Toxicology Reports, 2020;7:386-402. doi:10.1016/j.toxrep.2020.02.008
- Hu J, et al. "The safety of green tea and green tea extract consumption in adults - Results of a systematic review." Regulatory Toxicology and Pharmacology, 2018;95:412-433. doi:10.1016/j.yrtph.2018.03.019
- Maughan RJ, Griffin J. "Caffeine ingestion and fluid balance: a review." Journal of Human Nutrition and Dietetics, 2003;16(6):411-420. doi:10.1046/j.1365-277x.2003.00477.x
- Ruxton CH, Hart VA. "Black tea is not significantly different from water in the maintenance of normal hydration in human subjects: results from a randomised controlled trial." British Journal of Nutrition, 2011;106(4):588-595. doi:10.1017/S0007114511000456
- Hurrell RF, Reddy M, Cook JD. "Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages." British Journal of Nutrition, 1999;81(4):289-295. doi:10.1017/S0007114599000537
- Zijp IM, Korver O, Tijburg LB. "Effect of tea and other dietary factors on iron absorption." Critical Reviews in Food Science and Nutrition, 2000;40(5):371-398. doi:10.1080/10408690091189194
- Gardiner C, et al. "The effect of caffeine on subsequent sleep: A systematic review and meta-analysis." Sleep Medicine Reviews, 2023;69:101764. doi:10.1016/j.smrv.2023.101764
