Membrane glucocorticoid receptors (mGRs) are a group of receptors which bind and are activated by glucocorticoids such as cortisol and corticosterone, as well as certain exogenous glucocorticoids such as dexamethasone. Unlike the classical nuclear glucocorticoid receptor (GR), which mediates its effects via genomic mechanisms, mGRs are cell surface receptors which rapidly alter cell signaling via modulation of intracellular signaling cascades. The identities of the mGRs have yet to be fully elucidated, but are thought to include membrane-associated classical GRs as well as yet-to-be-characterized G protein-coupled receptors (GPCRs). Rapid effects of dexamethasone were found not be reversed by the GR antagonist mifepristone, indicating additional receptors besides just the classical GR.