Does coffee cause dehydration?

Dr Mark Porter / 30 May 2018 ( 02 January 2020 )

Dr Mark Porter answers a reader’s question about whether or not coffee’s diuretic effect can cause dehydration.

Q: love coffee – I have three to four cups of filtered a day – but am aware that it is a diuretic and can cause dehydration. Should I copy the Greeks and Turks and always drink water with mine?

A: Caffeine is indeed a diuretic (it promotes the formation of urine), but only at doses of 250 mg or more and taken over a short period (the equivalent of two and a half cups of filtered coffee drunk in one go). If you drink normal amounts of coffee throughout the day, it has no real diuretic effect.

However, while coffee may not significantly increase urine production, caffeine and other ingredients irritate the bladder, sending signals to the brain suggesting it is fuller than it is, so you might feel the need to pee more often.



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