Endorphins are a group of peptide substances produced by the brain and spinal cord, belonging to the family of endogenous opioid peptides. This family includes beta-endorphin, alpha-endorphin, and gamma-endorphin, which are derived from the cleavage of the precursor protein proopiomelanocortin (POMC). Endorphins are primarily expressed in the central nervous system and certain peripheral nervous tissues, where they bind to opioid receptors and participate in a variety of physiological functions such as pain modulation, emotion control, and stress response. The specificity of gene expression and its variants can affect an individual's sensitivity to pain and drug reactivity. Abnormal function of the endorphin system is associated with various disease states.