text: By definition, antagonists display no efficacy to activate the receptors they bind. Antagonists do not maintain the ability to activate a receptor. Once bound, however, antagonists inhibit the function of agonists, inverse agonists, and partial agonists. In functional antagonist assays, a dose-response curve measures the effect of the ability of a range of concentrations of antagonists to reverse the activity of an agonist. The potency of an antagonist is usually defined by its half maximal inhibitory concentration (i.e., IC value). This can be calculated for a given antagonist by determining the concentration of antagonist needed to elicit half inhibition of the maximum biological response of an agonist. Elucidating an IC value is useful for comparing the potency of drugs with similar efficacies, however the dose-response curves produced by both drug antagonists must be similar. The lower the IC the greater the potency of the antagonist, and the lower the concentration of drug that is required to inhibit the maximum biological response. Lower concentrations of drugs may be associated with fewer side-effects.