Mas-related G-protein coupled receptor member X2 is a protein that in humans is encoded by the MRGPRX2 gene. It is most abundant on cutaneous mast cells, sensory neurons, and keratinocytes.

Activation of MRGPRX2 on mast cells leads to IgE-independent type 1 hypersensitivity-like symptoms, also known as pseudoallergic reactions, although more rapid and brief. Medications identified to cause MRGPRX2 activation including neuromuscular blocking agents (NMBA) (except for succinylcholine), antibiotics like DNA gyrase inhibitor fluoroquinolones or cell wall synthesis inhibitor vancomycin (which caused Red Man syndrome), icatibant, leuprolide, and morphine.