Figure 3-23 Effects of various types of ligands on receptor responses. A full agonist produces complete (100%) activation of a receptor at high concentrations, whereas partial agonist binding results in less than 100% activation, even at very high concentrations. A neutral antagonist has no activity of its own. Inverse agonists can be thought of as "superantagonists" because binding of these ligands produces a response below the baseline response measured in the absence of drug. If the physiologic effect of the baseline levels of activated receptor (R*) is small, antagonists and inverse agonists may not be clinically distinguishable.