PRL and insomnia measurement: Another study with chronic migraine (CM) patients (compared to healthy controls) showed an abnormal pattern of hormones secreted in hypothalamus during the night: a phase-delay in melatonin peak and lower melatonin levels among CM patients with insomnia, suggesting a possible chronobiological dysfunction; a decreased prolactin peak, contributing to a possible hyperdopaminergic state; a higher cortisol concentration; but no difference in growth hormone secretion [21].