Giving rats a nightly IV dose of DSIP (or its phosphorylated version) changed when they were most active: they moved less at night (when they normally run around) and more during the day (when they usually sleep). The effect was stronger and happened faster with the phosphorylated form, suggesting DSIP does more than just help you fall asleep – it can actually re‑program your internal clock.

Daily intravenous evening injections of 30 nmol/kg DSIP (Delta Sleep-Inducing Peptide) in rats adapted to a constant 24 hr light:dark cycle produced changes in the circadian locomotor behavior. After 3 days the normally high locomotor activity during the dark phase was reduced while during the light (sleeping) phase the animals became relatively more active. Similar, but more rapid and more marked changes were observed (with the same schedule of injections) after 0.1 nmol/kg DSIP-P (the analogue of DSIP phosphorylated at the serine in position 7). In fact the peptide and its analogue induced a relative reversal or shift of the circadian locomotor activity phases opposite to the persisting light:dark conditions (=Zeitgeber). This suggests that DSIP exerts rather complex "programming" effects on the circadian activities and has more than just a sleep-inducing activity.