VU0152099 (30 µM) induces a dose-dependent leftward shift of the acetylcholine (ACh) concentration response curve (CRC) with maximal shifts of 30-fold observed with 30 µM. VU0152099 dose-dependently potentiates the response to an EC20 concentration of ACh with EC50 values of 1.2 µM, and increases the maximal response to ACh to approximately 130%. VU0152099 is a potent positive allosteric modulator that enhance the response of the M4 receptor to the endogenous agonist ACh.