What is pharmacodynamics?

pharmacodynamics It is the study of the effects of a drug on the body. This includes the analysis of its mechanism of action and the proportion between the dose and its biochemical and physiological effects.

The term pharmacodynamics originates from two words of Greek origin: pharmacy (drug, drug) and dynamis (strength).

To understand the object of study of pharmacodynamics, it is essential to know the concept of receiver or target: is the cellular structure with which the drug will interact selectively, so that it can fulfill its function in the body.

In other words, receptors are macromolecules with specific functions that, together with the drug, will generate one of these responses in the body:

  • Changes in enzyme activity. For example: drugs to control insulin levels.
  • Modifications in the ion channels. For example: local anesthetics.
  • Modifications in the structure or production of proteins. For example: pharmacological treatments with estrogens.

The discovery of the receptors is a contribution of the British pharmacologist John Newport Langley, who at the end of the 19th century proposed the existence of certain structures within the cell that bind with drugs.

See also Drug.

Mechanisms of drug action

Mechanism of action (MA) is understood as all the manifestations or reactions generated by a drug in the body. In this sense, the mechanisms of action depend on various factors related to the drug-receptor union, such as:


One of the doubts of the general population regarding the use of drugs is how a drug can have an effect on a specific part of the body without affecting others that may not require that medication. The answer lies in selectivity.

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Selectivity is the ability of a drug to bind only to specific receptors. The narrower the spectrum of receptors to which it can bind, the greater the selectivity and, therefore, the more specific the pharmacological effect will be.


It is the level of attraction that exists between the receptor and the drug, that is, the ability they have to form a stable union. The higher the affinity, the greater the chance that the drug will produce the desired effect.


Reversibility is understood as the ability of a drug to separate from its receptor. This feature is linked with affinity. The higher the affinity, the less reversibility and therefore, the effect of the drug will last longer.

intrinsic activity

It is the ability of a drug-receptor binding to produce the desired effect.


It is the amount of drug that is required to achieve a desired effect. This amount is expressed in milligrams (mg) and is known as the dose.


It is the maximum level of therapeutic response that a drug can offer. That is, it is a measure to know what is the greatest desired effect that a drug can provide.

See also Medication.

Pharmacological action and pharmacological effect

Pharmacodynamics studies both the action and the effect of drugs in order to create more effective drugs or safer doses, with a lower incidence of side effects.

pharmacological action

Pharmacological action is the changes or modifications produced by the drug in the body at submolecular, molecular, cellular or biochemical levels.

An example of pharmacological action are the changes in thermoregulatory functions produced by drugs designed to combat fever, known as antipyretics.

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pharmacological effect

On the other hand, the pharmacological effect are the visible effects of the pharmacological action.

An example of pharmacological effect of the fever medicine would be the decrease in body temperature.

In turn, the pharmacological effects can be of several types:

  • primary effect: are the expected effects for that drug.
  • Placebo effect: these are effects that are not related to the drug.
  • Side effect: are effects generated by the desired manifestations of the drug (primary effect)
  • toxic effect: these are effects produced by an excess of the recommended dose of the drug.
  • lethal effect: are biological manifestations produced by the drug that can lead to the death of the patient.

See also Pharmacology.