In addition to insomnia, the incidence of ADRs greater than 5% included: blood prolactin increased (21.1%), irritability (5.3%) and nausea (7.0%) in the 5 μg nalfurafine group; blood prolactin increased (8.8%) in the 2.5 μg nalfurafine group; blood prolactin increased (7.4%) and thirsty (7.4%) in the placebo group. Here, PRL is linked to insomnia.