Why does caffeine raise your blood pressure when it puts your kidneys into overdrive?

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Caffeine increased plasma renin activity by 57 per cent, plasma norepinephrine by 75 per cent and plasma epinephrine by 207 per cent. Urinary normetanephrine and metanephrine were increased 52 per cent and 100 per cent respectively. Mean blood pressure rose 14/10 mm Hg one hour after caffeine ingestion. There was a slight fall and then a rise in heart rate. Plasma caffeine levels were usually maximal one hour after ingestion but there was considerable individual variation. A 20 per cent increase in respiratory rate correlated well with plasma caffeine levels. Under the conditions of study caffeine was a potent stimulator of plasma renin activity and adrenomedullary secretion.


The mild diuretic effect does not compensate for the hypertensive effect which occurs early after ingestion.

  • OK I understand that empirically it increases blood pressure, but why? Diuretics normally lower blood pressure by reducing the water levels in the blood stream. Sorry I'm not a doctor so I don't have a quantitative measurement for overdrive.
    – Chloe
    Commented Mar 24, 2018 at 20:58
  • So it increases pressure faster than it lowers pressure?
    – Chloe
    Commented Mar 24, 2018 at 21:04
  • 1
    @Chloe It increases pressure more than it lowers pressure. The diuretic effect is very mild, as Graham explained.
    – Carey Gregory
    Commented Mar 24, 2018 at 22:20

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