INS and metabolic disease: Previous studies suggested that mechanisms of weight gain, overeating, and metabolic disorders are mediated by antagonists of multiple receptors especially H1 and serotonin 5-HT2C receptors.[20,21] Serotonin is known to play a role in glucose homeostasis, and 5-HT1A antagonism leads to a decrease in insulin secretion secondary to decreased pancreatic β-cell responsiveness to plasma glucose levels.[5] In an experiment with hamsters, insulin-secreting pancreatic β-cell apoptosis induced by olanzapine was observed.[22] However, in our study, no patient needed insulin treatment permanently.