By definition, a diuretic is a product that increases the body’s production of urine. Hence water, or any drink consumed in large volumes, is a diuretic. Importantly, urinating more does not inevitably lead to dehydration (excessive loss of body water).

Drinking simultaneously provides the body with fluid for absorption (avoiding dehydration) and initiates urine production. Depending on the urine losses that occur following drinking, a beverage might be more accurately described as a “poor _re_hydrator” if large fluid losses result.

Caffeine is a weak diuretic, and tolerance to this effect is acquired rapidly (in four to five days) with regular caffeine intake. What’s somewhat concerning is that this has been known for almost 100 years!

In 1928, a study involving three people showed that when participants consumed no caffeine for more than two months, a dose as little as half a milligram per kilogram of body mass (roughly the amount in half a cup of coffee) caused a “noticeable” increase in urine loss.