Medication interactions are one of the most important safety issues with methylene blue. It can inhibit monoamine oxidase A, which creates a meaningful risk of serotonin toxicity when combined with certain serotonergic medications. A systematic review identified serotonin-syndrome cases involving methylene blue and serotonin-reuptake inhibitors systematic review. Your clinician will therefore review antidepressants, stimulants, migraine medications, and other serotonergic drugs before prescribing it. Other considerations include G6PD deficiency, pregnancy, kidney function, and the fact that methylene blue can discolor urine or stool.