Pathophysiology
Clinical meaning
Second-generation antipsychotics (SGAs) cause metabolic derangements primarily through antagonism of histamine H1 receptors (increasing appetite and sedation leading to decreased activity), serotonin 5-HT2C receptors (disrupting satiety signaling in the hypothalamus), and muscarinic M3 receptors on pancreatic beta cells (impairing insulin secretion independent of weight gain). Olanzapine and clozapine carry the highest metabolic risk due to their strong H1 and 5-HT2C binding affinity, producing significant weight gain (average 4-10 kg in the first year), insulin resistance, dyslipidemia (elevated triglycerides and LDL, decreased HDL), and increased incidence of metabolic syndrome. The ADA/APA consensus guidelines established a structured monitoring protocol because SGA-treated patients have a 2-3 fold increased risk of developing type 2 diabetes and a 1.5-fold increased risk of cardiovascular mortality compared to the general population. Weight gain risk hierarchy among SGAs follows: clozapine > olanzapine >> quetiapine > risperidone >> aripiprazole = ziprasidone = lurasidone, guiding agent selection in metabolically vulnerable patients.