Actions of Drugs on the Body: Pharmacodynamics

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  • 0:00 Drugs & the Body
  • 0:31 Pharmacodynamics
  • 2:20 Agonists & Antagonists
  • 3:25 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov
The way that drugs interact with the body is called pharmacodynamics. This lesson defines this process and explains the concepts of agonism and antagonism.

Drugs and the Body

You know, when most people swallow a pill prescribed to them by the doctor, I think we can agree they don't really think about the fact that the drug will not only do something to the body but also that the body will do something to the drug. They are two different kinds of interactions between a drug and the body. This lesson will explain the former - what a drug does to the body - even though it's only half the story. Let's define pharmacodynamics.


Pharmacodynamics (PD) is, in short, what a drug does to the body. More technically, it refers to the study of how a certain concentration of a drug produces a biological effect by interacting with specific targets at its site of action. The first definition I gave you is very simple but not specific, and the specific definition is not very intuitive. So, let's figure out what pharmacodynamics is by expanding on the definition a bit more.

A drug exerts its biological effects by interacting with receptors located on tissues and organs throughout the body. The effect of the drug is, thus, dependent upon the drug binding to the receptor. If we increase the concentration of a drug at the place where a bunch of receptors are located, we can, thus, conclude that the intensity of the drug's effect will be larger with a greater concentration of the drug. This isn't always true by any means as other factors can influence the intensity of a drug's effects, but that's the basic gist of it. Regardless, let me give you a real world example of pharmacodynamics you can relate to.

If you mix one teaspoon of salt in a cup of water, it'll taste slightly salty. That salt is like a drug interacting with sensory taste receptors on your tongue. If we dump a cup of salt into a cup of water, we increase the concentration of salt. Now try drinking it. It's going to be one intense experience because we've increased the concentration of the salt but the number of sensory receptors has stayed the same.

This is what pharmacodynamics is about. It studies the relationship between a drug's concentration at its site of action and the resulting intensity of its therapeutic or toxic effects.

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