Is Tea a Diuretic?
A cup of black tea carries only about 47 mg of caffeine, well below the dose that triggers any diuretic effect. In controlled research, hot and iced tea kept people just as hydrated as plain water.
Quick answer
Is Tea a Diuretic?
Not meaningfully. A cup of black tea has only ~47 mg of caffeine (Mayo Clinic), far below the ~250-300 mg acute dose that triggers any diuretic effect (Maughan & Griffin 2003). In the Beverage Hydration Index, hot and iced tea kept 72 men as hydrated as water (Maughan 2016). At normal intake tea does not dehydrate you.
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Tea has a reputation as a diuretic because it contains caffeine, but the numbers don't support the worry. An 8 oz (240 mL) cup of brewed black tea contains only about 47-48 mg of caffeine, and green tea about 28-29 mg (Mayo Clinic) — a fraction of the ~250-300 mg acute dose at which caffeine produces a short-term diuretic effect, and then chiefly in people who have been off caffeine for days or weeks (Maughan & Griffin 2003). At standard serving doses, tea, coffee and soft drinks show no diuretic action, and habitual drinkers develop a profound tolerance. The strongest real-world evidence comes from the Beverage Hydration Index trial: when 72 men drank 1 L of hot tea or cold/iced tea, their 4-hour urine output was not different from water, giving a hydration index of about 1.0 (Maughan 2016). In other words, tea at normal intake counts toward your daily fluid — it does not dehydrate you.
Tea Caffeine vs the Diuretic Threshold
| Beverage / threshold | Caffeine | Effect on hydration |
|---|---|---|
| Brewed black tea (8 oz) | ~47-48 mg Far below the diuretic threshold; no diuretic action at this serving dose. | |
| Green tea (8 oz) | ~28-29 mg Even lower than black tea; counts toward daily fluid like water. | |
| Brewed coffee (8 oz, for comparison) | ~96 mg Roughly double black tea, still below the acute diuretic threshold per cup. | |
| Acute diuretic threshold | ~250-300 mg Caffeine stimulates urine output only above this acute dose, and mainly in caffeine-deprived people. That's roughly 5-6 cups of black tea at once. | |
| EFSA safe daily intake | up to 400 mg/day Habitual caffeine up to 400 mg/day (and single doses up to 200 mg) is judged safe for healthy non-pregnant adults. |
Why Tea Doesn't Dehydrate You
The caffeine dose is too small
A short-term diuretic response appears mainly above ~250-300 mg of caffeine taken acutely by caffeine-deprived people (Maughan & Griffin 2003). A cup of black tea has only ~47 mg (Mayo Clinic) — you'd need roughly 5-6 cups at once to approach the threshold.
Tea hydrates like water in trials
In the Beverage Hydration Index study, both hot tea and cold/iced tea produced 4-hour urine output that was not different from water (Maughan 2016). No beverage tested — including tea, coffee and lager — scored significantly below water, so none caused net dehydration at 1 L.
Habitual drinkers tolerate caffeine
Doses equivalent to standard servings of tea and coffee have no diuretic action, and regular drinkers develop a profound tolerance to caffeine's diuretic effect (Maughan & Griffin 2003). Daily tea drinkers see essentially no extra urine loss.
The diuretic effect is small anyway
A meta-analysis of 16 studies (28 effect sizes, mean dose 300 mg) found caffeine's diuretic effect small overall (0.29) — and exercise blunts it further (Zhang et al. 2015). Even at coffee-sized doses the net fluid loss is modest, and tea's dose is far smaller.
How to Count Tea Toward Your Hydration
- Count both hot and iced tea toward your daily fluid — in the Beverage Hydration Index they retained fluid just like water (Maughan 2016)
- Don't avoid tea fearing dehydration: a cup carries only ~47 mg caffeine, far below the ~250-300 mg diuretic threshold (Mayo Clinic; Maughan & Griffin 2003)
- Stay within EFSA's 400 mg/day caffeine guidance — that's roughly 8 cups of black tea, well beyond typical intake (EFSA 2015)
- If you're a habitual tea drinker, expect essentially no diuretic effect; tolerance develops with regular use (Maughan & Griffin 2003)
- Green tea is even lower in caffeine (~28 mg/cup), so it's an easy hydrating swap if you're caffeine-sensitive (Mayo Clinic)
- For post-exercise rehydration, remember exercise itself blunts any small caffeine diuretic effect (Zhang et al. 2015)
How Much Should You Actually Drink?
Tea counts toward your daily fluid. Get a personalized target based on your weight, activity, and climate.
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- black tea ~47 mg, green tea ~28 mg, coffee ~96 mg per 8 oz — An 8 oz cup of brewed black tea contains about 47-48 mg of caffeine, and green tea about 28-29 mg; brewed coffee about 96 mg.[5]
- diuretic threshold ~250-300 mg acute — Acute caffeine produces a short-term diuretic effect only at large doses of at least 250-300 mg, and chiefly in people deprived of caffeine for days or weeks; standard serving doses of tea show no diuretic action.[1]
- tea BHI ~1.0, not different from water (n=72, 1 L, 4 h) — When 72 men drank 1 L of hot tea or cold/iced tea, 4-hour urine output was not different from water; tea's beverage hydration index was about 1.0 and no beverage scored significantly below water.[2]
- effect size 0.29 overall (16 studies, 28 effect sizes) — A meta-analysis of 16 studies (28 effect sizes, mean dose 300 mg) found caffeine's diuretic effect small overall (0.29; 95% CI 0.11-0.48), and exercise blunts it further.[3]
- 400 mg/day habitual; 200 mg single dose — EFSA judges habitual caffeine intake up to 400 mg/day, and single doses up to 200 mg, safe for healthy non-pregnant adults; 200 mg/day for pregnant women.[4]
- [1]Maughan & Griffin 2003 (J Hum Nutr Diet) — Maughan RJ, Griffin J. Caffeine ingestion and fluid balance: a review. Journal of Human Nutrition and Dietetics. 2003 Dec;16(6):411-420.PMID: 19774754DOI: 10.1046/j.1365-277X.2003.00477.x
- [2]Maughan 2016 (Am J Clin Nutr) — Maughan RJ, Watson P, Cordery PA, Walsh NP, Oliver SJ, Dolci A, Rodriguez-Sanchez N, Galloway SD. A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index. Am J Clin Nutr. 2016 Mar;103(3):717-23.PMID: 26702122DOI: 10.3945/ajcn.115.114769
- [3]Zhang et al. 2015 (J Sci Med Sport) — Zhang Y, Coca A, Casa DJ, Antonio J, Green JM, Bishop PA. Caffeine and diuresis during rest and exercise: A meta-analysis. Journal of Science and Medicine in Sport. 2015 Sep;18(5):569-574.PMID: 25154702DOI: 10.1016/j.jsams.2014.07.017
- [4]EFSA 2015 (EFSA Journal) — EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA). Scientific Opinion on the safety of caffeine. EFSA Journal. 2015;13(5):4102.DOI: 10.2903/j.efsa.2015.4102
- [5]Mayo Clinic caffeine table — Mayo Clinic. Caffeine content for coffee, tea, soda and more. Mayo Foundation for Medical Education and Research.
Last reviewed: 2026-06-20. Every figure on this page is sourced to the named primary references above.
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Frequently Asked Questions
Is tea a diuretic?
Not meaningfully at normal intake. A cup of black tea contains only ~47 mg of caffeine (Mayo Clinic), far below the ~250-300 mg acute dose at which caffeine produces a short-term diuretic effect — and then mainly in people deprived of caffeine for days or weeks (Maughan & Griffin 2003). At standard serving doses, tea has no diuretic action.
Does tea dehydrate you?
No. In the 2016 Beverage Hydration Index study, 72 men drank 1 L of hot tea or cold/iced tea and produced no more urine over 4 hours than after drinking water, giving a hydration index of about 1.0 (Maughan 2016). No beverage tested — tea included — scored significantly below water, so tea does not cause net dehydration.
How much caffeine is in a cup of tea?
An 8 oz (240 mL) cup of brewed black tea contains about 47-48 mg of caffeine, and green tea about 28-29 mg (Mayo Clinic). For comparison, the same size cup of brewed coffee has roughly 96 mg — about double black tea. All of these are below the ~250-300 mg acute dose linked to any diuretic effect.
How many cups of tea would it take to be a diuretic?
Caffeine only stimulates urine output above roughly 250-300 mg taken acutely, and chiefly in people who haven't had caffeine for days or weeks (Maughan & Griffin 2003). At ~47 mg per cup of black tea (Mayo Clinic), that's roughly 5-6 cups consumed at once — far more than most people drink in a single sitting, and habitual drinkers tolerate even that.
Does tea count toward my daily water intake?
Yes. In the Beverage Hydration Index trial, both hot tea and cold/iced tea kept participants as hydrated as plain water, with 4-hour urine output not different from water (Maughan 2016). Because tea is retained like water, you can count it toward your daily fluid intake rather than dismissing it as a 'dehydrating' drink.
Is green tea a diuretic?
Not meaningfully. An 8 oz cup of green tea contains only ~28-29 mg of caffeine (Mayo Clinic) — even lower than black tea and far below the ~250-300 mg acute threshold for any diuretic effect (Maughan & Griffin 2003). At normal servings, green tea has no diuretic action and counts toward your daily fluid, much like water.
Does iced tea hydrate differently from hot tea?
No. In the Beverage Hydration Index study, both hot tea and cold/iced tea produced 4-hour urine output that was not different from water (Maughan 2016). Temperature doesn't change the hydration outcome — both forms had a hydration index of about 1.0, the same as plain water.
How much tea is safe to drink per day?
EFSA judges habitual caffeine intake up to 400 mg/day, and single doses up to 200 mg, safe for healthy non-pregnant adults (EFSA 2015). At about 47 mg per cup of black tea, 400 mg/day works out to roughly 8 cups — more than most people drink. Pregnant women are advised to stay under 200 mg/day.
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