β-Endorphin (1-27) (human) is an opioid antagonist that binds μ-, δ-, and κ-opioid receptors with Kis of 5.31, 6.17, and 39.82 nM, respectively. β-Endorphin (1-27) (human) inhibits β-Endorphin (HY-P1502)-induced and etorphine-induced analgesia.