Why can methylene blue interact dangerously with antidepressants, and who else should avoid it?

Methylene blue inhibits monoamine oxidase A, an enzyme involved in breaking down serotonin. Combining it with serotonergic medicines, including many antidepressants and some opioids, can cause serotonin syndrome. This can involve agitation, confusion, fever, muscle rigidity or twitching and unstable vital signs, and can be life-threatening. The FDA-approved intravenous product carries a boxed warning. Much of the reported clinical experience involves medical intravenous use; that does not establish a safe, interaction-free threshold for oral wellness products.[1][2]

G6PD deficiency is another major concern because methylene blue can cause severe breakdown of red blood cells; it is a contraindication in the prescribing information. Pregnancy, breastfeeding, kidney impairment and a history of reactions also require specific assessment. Anyone considering it needs a medication review that includes prescriptions, supplements and over-the-counter products. Stopping an antidepressant independently to make room for methylene blue creates its own risks and does not reliably remove an interaction immediately. New fever, confusion or marked muscle symptoms after a potentially interacting combination warrant urgent medical assessment.[1]