The effects of a drug are usually presented in a dose-response curve. The effect of the drug is plotted on the Y-axis and the dose on the X-axis (Figure 10). The dose is usually plotted on a logarithmic scale. The higher the dose the stronger the effect, until the effect levels off to a maximum. The effect is usually expressed as a percentage of the maximum. The maximum effect of one drug may be more than that of another. Desired and side effects can both be plotted in dose-response curves.

Figure 10: Dose-response curve

The dose is usually expressed per kilogram body weight or per m2 body surface area. However, the most accurate way is to use the plasma concentration, because it excludes differences in absorption and elimination of the drug. In the following text the plasma concentration-response curve (Cp/response curve) is used.