DSIP (Delta Sleep-Inducing Peptide) is a naturally occurring nonapeptide composed of nine amino acids (Trp–Ala–Gly–Gly–Asp–Ala–Ser–Gly–Glu). It has been studied in research settings for its role in neuropeptide signaling pathways, including mechanisms related to sleep regulation, stress response, pain modulation, and endocrine processes.