It’s a persistent myth, and it even sounds logical: tea contains caffeine, caffeine makes you urinate, so tea supposedly causes you to lose more water than it provides. Some people even go so far as to recommend drinking a glass of water with every cup, just to «compensate .» At Tisane Addict, we prefer to check the facts before repeating them. So we took a look at the clinical trials that have thoroughly examined this question—examining not only their results but also their limitations and funding sources. Here’s our detailed verdict.
1. Where did the idea that tea causes dehydration come from?
The starting point is a fact: caffeine—which is called theine in tea but is exactly the same molecule—has a diuretic effect. The problem stems from oversimplification. This effect has mainly been observed with high doses of caffeine—often administered in pill form—in people who did not normally consume it. A cup of tea, on the other hand, is almost entirely water, with a moderate amount of caffeine. Applying one to the other without taking measurements—that’s where the myth began.
2. What the Studies Say, Backed by Statistics
Ruxton & Hart, British Journal of Nutrition
21 healthy men, randomized crossover trial: 4 or 6 mugs (240 ml each) of black tea with a splash of milk (equivalent to 168 or 252 mg of caffeine), compared to the same amount of water. Result: No significant difference in blood and urine markers of hydration. Read the study
Maughan et al., *American Journal of Clinical Nutrition*
72 volunteers; 13 common beverages were tested, with one liter of each consumed. Over the next four hours, the amount of urine produced after drinking hot tea, iced tea, or coffee was no different from that observed after drinking water. Read the study
EFSA, Opinion on the Safety of Caffeine (2015)
The European Food Safety Authority considers that up to 400 mg of caffeine per day, from all sources, does not pose a safety concern for a healthy adult (200 mg for pregnant or breastfeeding women). View the review
To put this into perspective, here’s a quick calculation based on the 2011 study: 168 mg divided among 4 mugs equals about 42 mg of caffeine per mug of black tea under the study’s conditions. The 6 mugs consumed by the group with the highest intake therefore remained well below the 400 mg threshold set by the EFSA and did not tip the water balance.
3. True or False: 5 Common Misconceptions Put to the Test
«A cup of tea causes you to lose more water than it provides.» The two studies cited show no net loss compared to water at the tested concentrations.
«You should drink a glass of water for every cup of tea.» Nothing in these studies justifies this «compensation»: tea definitely counts toward your daily fluid intake.
«Caffeine has a diuretic effect.» Yes, but it is most noticeable at high doses and becomes less pronounced in regular consumers. At the levels typically consumed in tea, it was not detectable in the tests.
«Green tea is less dehydrating than black tea.» None of the studies cited compared the two. What actually varies is the amount of caffeine, depending on the tea leaves, the dosage, and the steeping time—not a property specific to the tea’s color.
«Herbal teas do not contain caffeine.» Verbena, chamomile, rooibos, raspberry leaves: these plants are not related to the tea plant and do not contain any tea. The only notable exception among common herbal teas is mate, which contains caffeine.
4. The Limits You Need to Know—Because We Owe You Honesty
These findings are solid, but they have limitations. The 2011 study involved 21 men at rest in a laboratory setting: its results cannot be carelessly extrapolated to intense physical exertion or extreme heat. Furthermore, both studies were funded by organizations with ties to the industry—the Tea Advisory Panel for the first, and the European Hydration Institute for the second. This does not invalidate them—they were published in peer-reviewed journals—but it is information we prefer to share with you rather than withhold.
Finally, «does not cause dehydration» does not mean «there are no limits.» Caffeine is still subject to the EFSA’s guidelines, and people who are sensitive to it would be better off switching to herbal tea in the evening, as we explained in our guide tea or herbal tea after a meal. If you have any questions regarding a specific medical condition, you should consult a healthcare professional.
Key Takeaways
- When consumed in normal amounts, tea does not cause dehydration: two clinical trials found no difference compared to water.
- Caffeine does have a diuretic effect, but it is associated with high doses.
- EFSA guideline: up to 400 mg of caffeine per day for a healthy adult.
- Herbal teas are caffeine-free, except for mate.
FAQ: Tea and Hydration
Does tea count toward the amount of water you drink each day?
According to the available clinical trials, yes: at the amounts tested (up to 6 mugs per day in the 2011 study), tea showed no difference from water in terms of hydration markers. Water remains the gold standard, but tea should not be excluded from the total.
Why do we feel the urge to urinate after drinking tea?
First, because we’ve just consumed a certain amount of liquid—as with a large glass of water. The 2016 study shows that, over a four-hour period, tea does not cause the body to produce more urine than the same amount of water.
How many cups of tea can you drink per day?
The official guideline focuses on caffeine, not on cups: the EFSA recommends 400 mg per day for a healthy adult, from all sources combined, and 200 mg during pregnancy or while breastfeeding. The caffeine content of a single cup varies depending on the type of tea, the amount used, and the steeping time, so you need to add this to your intake from coffee, sodas, and chocolate.
Does iced tea cause more dehydration?
No: The 2016 study tested iced tea in the same way as hot tea, finding no difference compared to water. Just be careful with highly sweetened store-bought versions—they’re a different story altogether: homemade iced tea is still the safest bet.