Does tea have any negative health effects?

December 12, 2025 •

3 min read

While tea is the second most consumed beverage globally, ranking only behind water, many are unaware that excessive consumption can lead to negative health effects. Research highlights how tea’s natural compounds, including caffeine and tannins, may cause undesirable side effects in some individuals if not consumed in moderation.

Quick Summary

Excessive consumption of tea, particularly high-caffeine varieties, can lead to side effects including increased anxiety, sleep problems, and compromised iron absorption. The tannins present can also cause digestive discomfort and tooth staining, highlighting the need for moderation to maintain optimal health.

Key Points

Iron Absorption: Tea's tannins can inhibit the body's absorption of non-heme iron from plant-based foods, which is especially important for vegans and those with anemia.
Caffeine Effects: Excessive intake of caffeine from tea can cause anxiety, restlessness, heart palpitations, and headaches, especially in sensitive individuals.
Sleep Disruption: Drinking caffeinated tea, particularly in the afternoon or evening, can disrupt sleep patterns by inhibiting the production of melatonin.
Digestive Issues: Strong tea or consumption on an empty stomach can lead to stomach irritation, nausea, acid reflux, or bloating due to its tannin and caffeine content.
Dental Staining: The high concentration of tannins in tea, especially black varieties, can cause significant discoloration and staining of tooth enamel over time.
Excessive Intake is the Main Issue: Most negative health effects are linked to overconsumption. Moderate intake (3-4 cups per day) is generally safe for most people.

Understanding the Culprits: Caffeine and Tannins

Most of the potential negative health effects of tea stem from two primary compounds: caffeine and tannins. While moderate amounts of both can be part of a healthy diet, overconsumption is where the problems arise. Individual sensitivity also plays a significant role in how these compounds are tolerated.

The Impact of Excessive Caffeine

Caffeine is a natural stimulant found in black, green, and oolong teas. While it can enhance focus and alertness, too much can lead to negative side effects.

Anxiety and Restlessness: High caffeine intake can trigger feelings of jitteriness, nervousness, and anxiety, particularly in sensitive individuals.
Sleep Disruption: Caffeine can interfere with sleep patterns by inhibiting the production of melatonin, the hormone that signals the body to sleep.
Headaches: While moderate intake can sometimes alleviate headaches, regular, excessive consumption or withdrawal can lead to chronic headaches.
Increased Heart Rate: Large doses of caffeine can cause an increased heart rate and palpitations.

Tannins and Iron Absorption

Tea is rich in a class of compounds called tannins, which are responsible for its bitter, dry taste. These compounds can bind to non-heme iron (iron from plant sources) in the digestive tract, preventing its proper absorption. This can be a significant concern for individuals with iron-deficiency anemia or those following a vegetarian or vegan diet. To minimize this effect, health experts recommend drinking tea between meals rather than with them.

Digestive System Discomfort

Excessive tea consumption, especially on an empty stomach, can lead to several digestive problems. The astringent nature of tannins can irritate the digestive lining, causing discomfort.

Stomach Upset and Acid Reflux

Stomach Irritation: Tannins can increase stomach acid production, which can lead to nausea, stomach ache, and acid reflux in sensitive individuals.
Exacerbating Conditions: For those with pre-existing conditions like gastritis or ulcers, the increased acidity can worsen symptoms.
Bloating: In some people, the diuretic and stimulating effects of caffeine can contribute to bloating and other discomforts.

Other Notable Negative Effects

Dental Staining

Tea's high tannin content can cause tooth discoloration over time, with black tea being a particular culprit. The darker the tea, the more likely it is to cause staining. Adding a splash of milk or practicing good oral hygiene can help mitigate this effect.

Skeletal Fluorosis

While very rare, excessive consumption of highly brewed tea (in volumes far exceeding normal intake) has been linked to skeletal fluorosis, a condition caused by the accumulation of fluoride in the bones. This was observed in an extreme case involving a woman who drank excessive amounts of strong tea daily.

Heavy Metal Contamination

Some studies have found traces of heavy metals like lead and aluminum in tea leaves, which can leach into the drink. While levels are generally considered safe, some health concerns have been raised, especially regarding long brewing times. Choosing high-quality tea and avoiding over-steeping can reduce exposure.

Comparing Tea Types: Potential Negative Effects


Feature	Black Tea	Green Tea	Herbal Tea	Decaf Tea
Caffeine Level	High (40-90mg/cup)	Moderate (20-45mg/cup)	None (most varieties)	Low (2-5mg/cup)
Tannin Content	High	Moderate	Low to None (depends on herb)	Low (less than caffeinated)
Iron Absorption Impact	High risk, especially with meals	Moderate risk, especially with meals	Minimal to none	Minimal to none
Digestive Issues	Higher risk of stomach upset and acid reflux due to higher caffeine and tannin levels	Moderate risk of stomach irritation if consumed on an empty stomach	Minimal risk; some herbs like peppermint can aid digestion	Minimal risk of caffeine-related issues
Dental Staining	Higher risk due to darker color and high tannin content	Moderate risk; can cause greyish stains over time	Lower risk; lighter color, but some can still stain	Lower risk than caffeinated teas

Conclusion: Moderation and Mindful Consumption are Key

While tea offers numerous health benefits, such as a rich source of antioxidants and improved cardiovascular health, it is not without potential downsides when consumed excessively. For most healthy adults, 3 to 4 cups of tea per day is considered a reasonable amount, though individual sensitivity to caffeine and tannins varies. Those at risk for iron deficiency or who experience digestive issues should be particularly mindful of their intake. By paying attention to your body’s response and practicing moderation, you can continue to enjoy tea's comforting warmth and unique flavors while minimizing any negative effects. For more detailed information on tea's various side effects, you can refer to authoritative sources like Healthline's article on the subject.

Frequently Asked Questions

Yes, excessive tea consumption can interfere with iron absorption, particularly non-heme iron from plant sources. The tannins in tea bind to the iron, making it unavailable to the body. This is more of a concern for individuals with low iron levels or those who are vegetarian/vegan.

For most healthy people, consuming more than 3 to 4 cups of caffeinated tea per day can increase the risk of negative side effects like anxiety, sleep issues, and digestive problems. However, individual tolerance varies significantly.

The caffeine content in tea can stimulate the nervous system, and if consumed in excess, it may lead to feelings of anxiety, jitters, and restlessness in some people, particularly those who are sensitive to caffeine.

Drinking strong tea or having it on an empty stomach can irritate the digestive lining and increase stomach acid, leading to nausea, stomach ache, heartburn, or acid reflux due to its tannin content.

Yes, the tannins in tea can cause discoloration and staining of tooth enamel. Darker teas like black tea are more likely to cause significant staining, but other teas can also cause discoloration over time.

Caffeinated teas (black, green, oolong) can disrupt sleep patterns if consumed too close to bedtime. Caffeine inhibits melatonin production, which can make it harder to fall asleep or reduce sleep quality.

Most herbal teas are naturally caffeine-free and generally considered safe. However, some herbal teas can have side effects or interact with medications. For example, some may contain pyrrolizidine alkaloids, which can be harmful to the liver if consumed in large quantities.

To prevent negative effects, practice moderation, drink tea between meals instead of with them to improve iron absorption, and avoid strong, highly brewed tea. If sensitive to caffeine, choose decaffeinated or herbal varieties.