How Much Caffeine Is Too Much?
Europe's food safety authority (EFSA) judges up to 400 mg of caffeine a day, and single doses of 200 mg, safe for healthy adults. A brewed coffee carries roughly 96 mg per 8 oz cup, so the math is easier than you think.
Quick answer
How Much Caffeine Is Too Much?
For healthy adults, EFSA (2015) judges up to 400 mg of caffeine per day — about four 8 oz brewed coffees at ~96 mg each (Mayo Clinic) — and single doses up to 200 mg safe, with no safety concern. Pregnant women should stay at or below 200 mg/day. Above these amounts is more than EFSA's reviewed safe range.
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The European Food Safety Authority (EFSA 2015) concluded that habitual caffeine intakes up to 400 mg/day, and single doses up to 200 mg (about 3 mg/kg for a 70-kg adult), raise no safety concern for healthy non-pregnant adults; pregnant women should stay at or below 200 mg/day. Translating that into cups is straightforward: an 8 oz (240 mL) brewed coffee averages ~96 mg caffeine, brewed black tea ~47 mg, and green tea ~28 mg (Mayo Clinic reference averages). So 400 mg/day is roughly four 8 oz coffees. A related worry — that caffeine dehydrates you — is largely unfounded at these intakes: a short-term diuretic effect appears only above ~250-300 mg taken acutely by people who are caffeine-deprived (Maughan & Griffin 2003), and habitual drinkers develop tolerance. In a free-living trial, men consuming a mean 308 mg/day of caffeine from coffee showed no difference from water in total body water or 24-hour urine output (Killer et al. 2014).
Safe Caffeine Limits and Per-Cup Content
| Item | Amount | Source |
|---|---|---|
| Habitual daily limit (healthy adults) | Up to 400 mg/day EFSA judges habitual intakes up to 400 mg/day safe for healthy non-pregnant adults. That's roughly four 8 oz brewed coffees. | |
| Single-dose limit (healthy adults) | Up to 200 mg A single dose up to 200 mg (~3 mg/kg for a 70-kg adult) raises no safety concern, including before exercise. | |
| Pregnancy limit | 200 mg/day EFSA recommends pregnant women keep total caffeine at or below 200 mg/day. | |
| Brewed coffee (8 oz / 240 mL) | ~96 mg Standard reference average for brewed coffee. About four cups reaches the 400 mg daily limit. | |
| Brewed black tea (8 oz / 240 mL) | ~47 mg Roughly half the caffeine of brewed coffee per cup. | |
| Green tea (8 oz / 240 mL) | ~28 mg About a third of a coffee's caffeine, well below any diuretic threshold. |
Does That Much Caffeine Dehydrate You?
The Diuretic Threshold Is High
Caffeine only stimulates urine output at large acute doses of at least 250-300 mg (the amount in 2-3 cups of coffee), and mainly in people who have been off caffeine for days or weeks (Maughan & Griffin 2003). Standard servings show no diuretic action.
Habitual Drinkers Build Tolerance
Regular coffee and tea drinkers develop a profound tolerance to caffeine's diuretic effect, so normal daily servings do not cause fluid loss exceeding the volume you drank (Maughan & Griffin 2003).
Coffee Hydrates Like Water
In a free-living crossover trial, 50 habitual drinkers having a mean 308 mg caffeine/day from coffee showed no difference from water in total body water (51.5 vs 51.4 kg) or 24-hour urine (2409 vs 2428 mL) — coffee counts toward your daily fluid (Killer et al. 2014).
The Effect Is Small Overall
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). Only at ~6 mg/kg (~537 mg) does an acute dose meaningfully raise urine output (Seal et al. 2017).
Staying Within Safe Caffeine Limits
- Treat ~400 mg/day as your ceiling if you're a healthy adult — about four 8 oz brewed coffees (EFSA 2015)
- Keep any single serving at or below 200 mg, roughly two average 8 oz coffees in one sitting (EFSA 2015)
- If you're pregnant, cap total caffeine at 200 mg/day from all sources, not just coffee (EFSA 2015)
- Swap to black tea (~47 mg) or green tea (~28 mg) per cup when you want the ritual with far less caffeine (Mayo Clinic)
- Don't avoid coffee to 'stay hydrated' — at habitual intakes it counts toward your daily fluid like water (Killer et al. 2014)
- Remember a short-term diuretic bump only shows up above ~250-300 mg taken acutely after a caffeine break (Maughan & Griffin 2003)
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Use the Hydration CalculatorSources & Citations
- 400 mg/day — EFSA judges habitual caffeine intake up to 400 mg/day safe for healthy non-pregnant adults.[1]
- 200 mg single dose — EFSA judges single caffeine doses up to 200 mg (~3 mg/kg for a 70-kg adult) safe, including before exercise.[1]
- 200 mg/day in pregnancy — EFSA recommends pregnant women keep total caffeine at or below 200 mg/day.[1]
- Coffee ~96 mg, black tea ~47 mg, green tea ~28 mg per 8 oz — Caffeine per 8 oz (240 mL) serving: brewed coffee ~96 mg, brewed black tea ~47 mg, green tea ~28 mg (standard reference averages).[2]
- >=250-300 mg acute threshold — Acute caffeine produces a short-term diuretic effect only at large doses of at least 250-300 mg, chiefly in caffeine-deprived people; standard servings have no diuretic action.[3]
- Mean 308 mg/day; TBW 51.5 vs 51.4 kg; urine 2409 vs 2428 mL — Habitual coffee drinkers consuming a mean 308 mg/day showed no difference from water in total body water (51.5 vs 51.4 kg) or 24-hour urine volume (2409 vs 2428 mL).[4]
- 16 studies (28 effect sizes); ES 0.29 overall, 0.54 without exercise — A meta-analysis of 16 studies (28 effect sizes, mean dose 300 mg) found caffeine's diuretic effect small overall (0.29), rising to moderate (0.54) when exercise studies are excluded.[5]
- 6 mg/kg (~537 mg) diuretic; 3 mg/kg (~269 mg) not — Coffee at 6 mg/kg caffeine (~537 mg) induced acute diuresis (613 mL vs 356 mL for water over 3 h), while 3 mg/kg (~269 mg) did not disturb fluid balance.[6]
- [1]EFSA 2015 — 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
- [2]Mayo Clinic caffeine table — Mayo Clinic. Caffeine content for coffee, tea, soda and more. Mayo Foundation for Medical Education and Research.
- [3]Maughan & Griffin 2003 — 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
- [4]Killer et al. PLoS ONE 2014 — Killer SC, Blannin AK, Jeukendrup AE. No evidence of dehydration with moderate daily coffee intake: a counterbalanced cross-over study in a free-living population. PLoS ONE. 2014 Jan 9;9(1):e84154.PMID: 24416202DOI: 10.1371/journal.pone.0084154
- [5]Zhang et al. 2015 — 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
- [6]Seal et al. Frontiers in Nutrition 2017 — Seal AD, Bardis CN, Gavrieli A, et al. Coffee with High but Not Low Caffeine Content Augments Fluid and Electrolyte Excretion at Rest. Frontiers in Nutrition. 2017 Aug;4:40.DOI: 10.3389/fnut.2017.00040
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
How much caffeine is too much per day?
For healthy non-pregnant adults, EFSA (2015) judges habitual intakes up to 400 mg of caffeine per day safe, with no safety concern. That's roughly four 8 oz brewed coffees at ~96 mg each. Above 400 mg/day moves beyond EFSA's reviewed safe range. Pregnant women should stay at or below 200 mg/day. Individual sensitivity varies, so cut back if you notice jitteriness or sleep disruption.
What is the safe caffeine limit in a single dose?
EFSA (2015) found that a single dose of caffeine up to 200 mg — about 3 mg/kg for a 70-kg adult, or roughly two average 8 oz coffees — raises no safety concern for healthy adults, including when taken before exercise. Spacing your intake across the day, rather than one large hit, keeps you within both the 200 mg single-dose and 400 mg daily guidance.
How much caffeine is in a cup of coffee versus tea?
Using Mayo Clinic reference averages per 8 oz (240 mL) serving: brewed coffee contains about 96 mg of caffeine, brewed black tea about 47 mg, and green tea about 28 mg. So a cup of coffee carries roughly twice the caffeine of black tea and over three times that of green tea. These are standard reference averages, not exact measured values, and brewing strength changes the real amount.
How much caffeine is safe during pregnancy?
EFSA (2015) recommends that pregnant women keep total caffeine intake at or below 200 mg per day from all sources combined. That's about two 8 oz brewed coffees (~96 mg each), or one coffee plus a couple of cups of tea. Because caffeine reaches the fetus, counting tea, soft drinks, chocolate and any energy drinks toward the 200 mg total matters.
Does caffeine dehydrate you?
Not at normal intakes. Caffeine has a short-term diuretic effect only at large acute doses of at least 250-300 mg taken by people who have been off caffeine for days or weeks (Maughan & Griffin 2003); habitual drinkers build tolerance. In a free-living trial, men having a mean 308 mg/day from coffee showed no difference from water in total body water or 24-hour urine (Killer et al. 2014). Coffee counts toward your daily fluid.
How many cups of coffee can I drink a day?
Roughly four 8 oz brewed coffees, since each averages about 96 mg of caffeine (Mayo Clinic) and EFSA (2015) sets the safe habitual daily limit at 400 mg for healthy adults. Keep any single serving to about two cups (200 mg) at once. If you're pregnant, the limit is 200 mg/day — about two cups total across the whole day.
Is green tea a diuretic?
Not meaningfully. An 8 oz cup of green tea contains only about 28 mg of caffeine (Mayo Clinic), far below the ~250-300 mg acute threshold needed for any diuretic effect (Maughan & Griffin 2003). At normal servings green tea has no diuretic action and counts toward your daily fluid intake, much like water.
Does caffeine before exercise cause a problem?
No. EFSA (2015) concluded that single caffeine doses up to 200 mg before exercise raise no safety concern for healthy adults. A meta-analysis of 16 studies (Zhang et al. 2015) also found that exercise actually blunts caffeine's already-small diuretic effect, so a pre-workout coffee within these limits does not undermine your hydration.
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