FIGURE 4

Hypothetical dose–response curves for four molecules with different patterns of efficacy. The system is constitutively active (fractional effect=0.4) and then placed under an additional endogenous agonist tone to a level of 0.6 fractional effect. A partial agonist decreases the endogenous tone but imposes its own intrinsic activity on the system, a neutral competitive antagonist abolishes the endogenous tone but does not eliminate constitutive activity, a protean agonist reduces the constitutive activity somewhat but imposes its own intrinsic effect and an inverse agonist abolishes both the endogenous tone and the constitutive activity.