Diuretics and High Blood Pressure
A diuretic (often called a water pill) is a substance that increases the volume of urine (increases diuresis).
An example of a mild diuretic is caffeine. Those who rarely drink coffee, often notice that there is a temporary increase in urination, after drinking strong coffee.
Why would you want to increase the amount of urine?
Blood pressure is the force which blood, mainly a liquid, exerts on the walls of the blood vessels. If the volume of urination is increased, the amount of fluid in the body is reduced. This leads to a decrease in the volume of the blood. A smaller volume of blood does not exert as much force on the walls of the blood vessels, so there is a decrease in blood pressure.
Some diuretics also increase the amount of sodium in the urine.
In addition to increasing the urine flow some diuretics will increase the rate of loss of sodium from the body (natriuresis). This loss of sodium (and accompanying chloride) also results in a decrease in the amount of body fluid.
After a period of time the body starts to at least partially compensate for the effects of diuretics (otherwise the body would dry up and sodium levels get too low), however diuretics continue to lower blood pressure.
Classes of Diuretics
There are three classes of diuretics that are used for treating high blood pressure.