log dose plot

Drug doses often span an enormous range — from micrograms to grams — so plotting effect against raw dose squashes everything important into the far left of the graph. The log dose plot fixes this by putting dose on a logarithmic axis, spreading the low doses out and turning the curve into a manageable S-shape.

On linear axes the graded dose–response curve is a rectangular hyperbola that rises fast and flattens. Take the logarithm of dose and that same data becomes a symmetrical sigmoid whose central portion, around the EC50 or ED50, is very nearly a straight line. This linearization is the practical payoff: the steepest middle section is where the curve carries the most information and where interpolation is most reliable.

The log dose plot is the standard canvas of pharmacology because it makes potency and efficacy easy to read and lets curves of widely differing potencies be compared side by side. Parallel shifts of a sigmoid along the log-dose axis are the visual signature of competitive antagonism, while a depressed plateau signals reduced maximal effect. The format is descriptive, not mechanistic — it reshapes the same data for clearer reading.