Aly M, et al. - In this prospective, randomized study, researchers determined the incidence, severity, and relation of morphine-induced pruritus to serum serotonin level among parturients who underwent elective cesarean delivery under spinal anesthesia and received an intrathecal injection of 0.5% (2-3 mL) hyperbaric bupivacaine in addition to 100 μg of morphine (group M100) and 200 μg of morphine (group M200). In the M100 group and M200 group, the reported incidence of pruritus was 55% and 75%, respectively. In addition, postoperative pruritus severity was significantly higher in group M200 than in group M100 at six and eight hours; but not at other times. A significant postoperative increase in serum serotonin level was noted in both groups, suggesting a role of serotonin in the genesis of intrathecal morphine-induced pruritus.