The study of the mechanism of drug actions is called pharmacodynamics. Most (but not all) drugs exert their action by binding to specific RECEPTORS. This binding may initiate changes that lead to the characteristic effects of the drug on body functions.

A central question in drug therapy (medication) is the proper dose of the drug that produces a desired action without many harmful side effects. To clarify this problem, pharmacologists analyze the relationship between dose and response. Most dose-response curves are sigmoidal (shaped like an S).

The log-dose-response can be viewed as having four parameters: potency, slope, maximal efficacy, and variability. Potency describes the strength of drug effects. It is usually employed to calculate relative strengths among drugs of the same class. Slope is the central part of the curve that is approximately straight. It...