A woman in her 50s presented to the hospital with a chief complaint of headache and nausea. Graves' disease was diagnosed based on positive blood test results for thyrotoxicosis and TSH receptor antibody and ultrasonographic thyroid gland findings. The patient was hospitalized and started treatment with thiamazole; however, after hospitalization, psychiatric symptoms, such as visual and auditory hallucinations, appeared, and she fulfilled the diagnostic criteria for thyroid crisis. We increased the dose of thiamazole and added potassium iodide. Thyroid function improved; however, the patient experienced reemergence of psychiatric symptoms. Blood tests revealed pseudohyperchloremia, which led to the discovery of abuse of over-the-counter analgesics containing bromwarelyl urea. The psychiatric symptoms were suspected to be due to withdrawal from chronic bromine intoxication. After starting psychotropic drugs, the patient's psychiatric symptoms became mild, her thyroid function continued to improve steadily, and she was discharged from the hospital. Thyroid crisis is a condition that should be suspected and treated at an early stage; however, the diagnostic criteria for thyroid crisis can be false-positive if the thyroid disease is accompanied by other conditions that cause psychiatric symptoms.