(A) ACh binds to the orthosteric pocket of the M1-mAChR to activate the receptor, resulting in induction of conformational changes within the receptor. This leads to coupling of the receptor to G proteins and β-arrestin with equivalent potencies, and subsequent activation of multiple signalling pathways downstream of G proteins and β-arrestin. (B) Binding of an ‘unbiased’ PAM-agonist to the M1-mAChR allosteric pocket potentiates coupling to G proteins and β-arrestin with equivalent potencies, but results in enhanced activation of multiple signalling pathways downstream of G proteins and β-arrestin. (C) Pilocarpine is biased towards G protein signalling over β-arrestin signalling, hence binding to the orthosteric pocket of the M1-mAChR results in receptor conformations that promote coupling to G proteins with greater potency than to β-arrestin. This results in activation of signalling pathways downstream of G proteins over β-arrestin.