It depends on the diuretic. You can basically overpower any diuretic by drinking fluids. If you’re taking, say, a thiazide diuretic for high blood pressure, it’s actually not a particularly strong diuretic and the mechanism of long term blood pressure lowering isn’t actually through diuresis (we don’t actually know what the mechanism is). However, if you are taking a diuretic for heart failure or edema (a loop diuretic like Lasix would be used in this case), you actually have excess fluid just sitting on your body. The idea is that you deplete the fluid in your blood vessels and the fluid in the extravascular compartment moves into the blood vessels.
Also of note, diuretics don’t decrease absorption of fluid, they increase excretion. But you are correct in that diuretics can put you at higher risk for dehydration.
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