Abstract Disclosure: A. Mandhan: None. N. Friedman: None. S. Stefan: None. Background: Olanzapine, an atypical antipsychotic, is commonly used to treat a variety of mental health conditions, including schizophrenia, bipolar disorder, and depression. Acute pancreatitis from olanzapine is rare. Drug-induced pancreatitis represents 0.1-2% of all cases of acute pancreatitis. Here we describe a case of olanzapine induced severe pancreatitis and new onset of diabetes. Clinical Case: A 43-year-old male with history of bipolar disorder was admitted with vomiting and altered mental status. Symptoms began a week prior to presentation and included polydipsia and polyuria. He had no known history of hyperlipidemia, diabetes or alcohol use. He was treated with olanzapine for six months prior to presentation, and the dose was increased to 35mg/day one month prior to hospital admission. On exam, he appeared older than his stated age, confused, restless and dehydrated. He was afebrile but tachycardic and hypotensive. Laboratory evaluation was notable for glucose of 1619 mg/dL (70-140 mg/dL) metabolic acidosis with ketonuria, lipase level of 684 U/L (n<60), and triglyceride (TG) level of 1574 mg/dL (<150 mg/dL). CT of the abdomen showed severe acute interstitial pancreatitis with retroperitoneal fluid and possible necrosis, normal-appearing gallbladder, no cholelithiasis. He was made NPO, and started on IV fluids and IV Insulin therapy. His HbA1C was 12.6% with negative GAD and IA2 antibodies, consistent with type 2 diabetes. Within twenty-four hours of presentation his DKA resolved, and TG levels down trended below 1,000 mg/dL. He was transitioned to subcutaneous insulin and combination therapy of fenofibrate. The patient was discharged on basal insulin, metformin, fenofibrate, a low dose statin and omega-3 fatty acids. His TG at discharge was 210 mg/dL and olanzapine was not restarted. Conclusions: Olanzapine induced pancreatitis has been described as a rare cause of pancreatitis in the literature. To date, there is only one additional case report about acute necrotizing pancreatitis from olanzapine. Given the ubiquitous use of olanzapine in treating psychiatric disorders, it is important that physicians are aware of this rare but potentially life-threatening adverse reaction. The exact mechanism by which olanzapine causes pancreatitis is unclear, and case reports suggest hypertriglyceridemia as the most common proposed etiology of olanzapine-induced acute pancreatitis. Patients should have a screening lipid panel before beginning therapy to optimize treatment outcomes. Presentation: Saturday, June 17, 2023