Pharmacodynamics is the scientific study that explores the biochemical, cellular, and physiological effects of drugs on the body.

Most drug effects result from their interactions with drug receptors or targets to trigger a cellular or systemic response.

Drug receptors can be found on cell surfaces and in specific intracellular compartments like the nucleus or extracellular compartments.

Additionally, drugs may interact with acceptors such as serum albumin, which do not directly alter physiological responses but instead affect a drug's pharmacokinetics.

The strength of the reversible interaction between a drug and its receptor, measured by the dissociation constant, defines its affinity.

A drug's chemical structure determines its receptor affinity, intrinsic activity, and specificity.

Drugs that interact with specific single-type receptors on particular cells exhibit high specificity, while those acting on ubiquitously expressed receptors have widespread effects.

Understanding these pharmacodynamic principles is vital for creating safe, targeted, and effective drugs.