High blood pressure drugs . . .

. . . how they work

This page gives a little bit more detail that helps to explain how high blood pressure drugs work.

Resisting the flow

The heart pushes blood round the body and the force with which it does this is what creates blood pressure. As explained, if you increase resistance, the pressure has to go up to effectively push blood to all parts of the body.

Physiologists worked out a simple law that describes the relationship between blood pressure, blood flow and resistance:

Blood pressure = blood flow (the amount the heart is pumping) x resistance (of the blood vessels.) Or as they write it BP=cardiac output x total peripheral resistance.

If you don't like maths, the relationship can be easily explained as follows. . .

Assuming everything else remains the same then:If cardiac output (or blood flow round the body) goes up, then blood pressure goes up.

Put another way, if your heart rate goes up, or your heart pumps more powerfully, output rises - then your blood pressure goes up. Of course, the opposite holds true which is why some drugs are able to reduce blood pressure by reducing the output of the heart. The rate and/or force of contraction is reduced and the blood pressure goes down.


If resistance goes up (i.e. the blood vessels constrict) then the blood pressure will go up. (Resistance is often called peripheral resistance by the scientists).

Again, the opposite is true. If blood vessels relax, resistance - and therefore blood pressure - goes down. Some high blood pressure treatments work by reducing peripheral resistance.

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This page was last modified on : May 12, 2011.