If pharmacokinetics describes the molecule's journey, pharmacodynamics describes its effect. It starts from the interaction with a target (usually a receptor, sometimes an enzyme or a channel) and follows the chain of signals to the measurable response.
Its central tool is the concentration-response curve: as concentration rises, the effect grows up to a maximum. From that curve come potency (EC50), maximum efficacy and the slope, which shows how quickly the response moves from minimum to maximum.
Pharmacodynamics also studies how the response changes over time: receptor desensitisation, tolerance, effects that persist after the molecule has been cleared, or those that depend on the pulsatility of the signal, as in the growth hormone or reproductive axes.
Telling pharmacokinetics from pharmacodynamics helps you read a study correctly: an effect that disappears may be because the compound was cleared (kinetics) or because the receptor stopped responding (dynamics).
Related terms
Learn it in depth at the Peptide University
- Pharmacodynamics: receptors and signaling · Module 2
- Safety profiles by class · Module 10
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