Abstract Disclosure: K. Tiwari: None. F. Sajid: None. J.G. Karam: None. Introduction: Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist used for the treatment of type 2 diabetes mellitus and weight management. Common side effects, primarily gastrointestinal (>10%), include nausea, vomiting, diarrhea, and constipation. Here, we present a case of acute sigmoid diverticulitis with an adjacent abscess in a patient who was recently initiated on GLP-1 receptor agonist therapy. Case presentation: A 76-year-old female with a medical history of type 2 diabetes mellitus on metformin and empagliflozin, hypertension, chronic kidney disease stage 3A, obesity (BMI: 43), and no known history of diverticulosis was started on semaglutide for additional glycemic, renal, and weight loss benefits, given suboptimal control of her obstructive sleep apnea, blood pressure, and knee arthritis. She received semaglutide subcutaneously at a dose of 0.25 mg weekly for 4 weeks, followed by an increased dosage of 0.5 mg for one week. However, she experienced a slight worsening of underlying constipation as a side effect. On the sixth week of therapy, she started having progressive lower abdominal pain with nausea, chills, and diarrhea, for which she presented to the Emergency Department. She was found to have leukocytosis, and a Computed Tomography (CT) of the abdomen/pelvis revealed peri-colonic fat stranding in the mid-ascending colon, wall thickening in the distal sigmoid colon, and a low-density fluid collection abutting the sigmoid/descending colonic wall, indicative of diverticulitis with a small abscess. She was admitted to the hospital for six days and was treated conservatively with Intravenous (IV) antibiotics, and her diet was slowly advanced as tolerated. Semaglutide was discontinued, and the patient was discharged home with outpatient endocrinology and gastrointestinal follow-up. A post-discharge colonoscopy showed diffuse diverticulosis. Conclusion: Constipation and old age are common risk factors for diverticulitis. While GLP1-1 receptor analogs have proven significant and multiple benefits, more knowledge about associated gastrointestinal complications resulting from slower food transit in the gastrointestinal tract is emerging. Older patients with underlying constipation and/or diverticulosis should particularly be monitored and treated for worsening constipation to avoid complications such as acute diverticulitis. Vigilance and awareness in recognizing and managing this potential complication are crucial with the wider indications and use of GLP-1 receptor analogs. Presentation: 6/3/2024