The article presents a case study of a 69-year-old woman who had auditory hallucination, self-talked, declined cognitive function, and who had been previously diagnosed with schizophrenia. She developed delirium caused by the use of fluconazole and due to cholinergic deficiency. Also noted are the needs to monitor a patient's mental status after fluconazole administration, and to identify and manage adverse drug reaction (ADR) promptly to maintain patient health.