Delta-sleep inducing peptide (DSIP) is found in neurons, peripheral organs, and plasma. DSIP was shown to induce mainly delta-sleep in rabbits, rats, mice, and humans. The peptide has been observed to affect electrophysiological activity, neurotransmitter levels in the brain. DSIP has been used to reduce withdrawal symptoms in alcoholic and opiate addicts and as an analgetic in chronic pain.