Any of a class of three endogenous opioids—α‎‐, β‎‐ and γ‎‐endorphins—found naturally in brain and other tissues that have pain-relieving effects similar to those of morphine. They are released during physical or emotional stress, such as childbirth or strenuous exercise, and can produce feelings of euphoria. All are peptides or polypeptides derived from the precursor pro-opiomelanocortin; for example, β‎‐endorphin is a 31-amino-acid peptide. The endorphins mediate their analgesic effects by binding to opioid receptors. See also dynorphin; enkephalin.