Figure 1.

Schematic diagram of types of positive allosteric modulator (PAM) effects on concentration-response curves. Three different types of PAM effect are displayed on concentration-response curves (for illustration purposes only, curves are hand-drawn). A Type I effect is defined as increasing the maximum response without a change in EC₅₀ value. A Type II effect is defined as a left-ward shift in the concentration-response curve (and a reduction in the EC50 value) without affecting efficacy (maximum response). A mixed Type I/II effect is defined as both a left-ward shift in concentration-response curve and an increase in efficacy (maximum response).