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I keep reading statements like this (this one from a BBC news article, talking about alcohol and mangoes), and get suspicious that there is a misunderstanding somewhere:

It acts as a powerful diuretic, causing you to urinate more, meaning you become dehydrated.

It seems to me that it would be one of these:

It acts as a powerful diuretic, causing you to urinate more, meaning your bladder gets emptied more often, but otherwise not altering the water levels in your body. Diuretics are mainly a problem just before bed and on long car journeys.

Or:

It acts as a powerful diuretic, meaning more of your body's water gets redirected to the bladder, even more than the water in the diuretic drink, and so you end up with a net loss of water in the body.

I thought "diuretic" had the former meaning (you want to empty your bladder more often) but I'd love to have a proper medical reference, or see some solid scientific research.

  • BTW, this chronicleflask.com/2015/08/29/… reminded me of the Horizon programme, where identical amounts of urine were produced (i.e. identical levels of dehydration) from heavy drinking vs. light drinking (of alcohol). The discussion in the comments was interesting, too. – Darren Cook Jun 25 '17 at 21:39
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A diuretic increases diuresis, which means it causes your kidneys to excrete more urine. It has nothing to do with your bladder and both of those definitions you quote are wrong, especially the one saying it doesn't alter the water levels in your body. Diuretics definitely reduce the water levels in your body; that's the most common reason for taking them. The second quote is wrong by saying they cause water to be redirected to the bladder. There's no redirection involved. Water is removed from your system the same way whether you take a diuretic or not. It's simply removed faster with a diuretic.

Wikipedia has a good summary of their medical uses:

In medicine, diuretics are used to treat heart failure, liver cirrhosis, hypertension, influenza, water poisoning, and certain kidney diseases. Some diuretics, such as acetazolamide, help to make the urine more alkaline and are helpful in increasing excretion of substances such as aspirin in cases of overdose or poisoning. Diuretics are often abused by those with eating disorders, especially bulimics, in attempts to lose weight.

The antihypertensive actions of some diuretics (thiazides and loop diuretics in particular) are independent of their diuretic effect.[citation needed] That is, the reduction in blood pressure is not due to decreased blood volume resulting from increased urine production, but occurs through other mechanisms and at lower doses than that required to produce diuresis. Indapamide was specifically designed with this in mind, and has a larger therapeutic window for hypertension (without pronounced diuresis) than most other diuretics.

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    I believe the question is about the popular assertion that you might as well not drink a diuretic liquid, because it causes your body to excrete more liquid than you just took in, leaving you as dehydrated as before if not more so. Anecdotally I think it's nonsense; I knew many adults who only drank tea, coffee, and beer, and were alive. Yet it is a common claim - not about diuretic meds, but about drinks that have a diuretic effect. – Kate Gregory Jun 26 '17 at 11:52
  • @KateGregory Hmm... maybe you're right. I'll add some additional material to address that. – Carey Gregory Jun 26 '17 at 13:35

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