This article reports a case of a patient with Crohn's disease who had 1 to 2 loose stools per day, occasionally with a small amount of bloody stool. Despite treatment with multiple drugs in the past, the disease was still poorly controlled. The patient was switched to upadacitinib extended-release tablets 45 mg once daily for oral administration. The patient's hemoglobin level decreased continuously, with the lowest value of 68 g·L^-1. After evaluation, it was determined that the decrease in hemoglobin was very likely related to upadacitinib extended-release tablets. The upadacitinib was discontinued, and vedolizumab was used for continued treatment. Symptomatic treatment was also given, and the patient's hemoglobin level gradually recovered. This article analyzes the clinical characteristics of upadacitinib-induced hemoglobin reduction in this case and the treatment plan optimization process, to provide a reference for safe clinical medication.

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