Methylene blue

The verdict

Our read at a glance.

Whether a drug approved to reverse methemoglobinemia improves cognition or mitochondrial function in healthy people.

The signal

The approved use is solid and narrow: methylene blue is the standard antidote for acquired methemoglobinemia, where it accelerates the reduction of methaemoglobin back to functional haemoglobin, and that indication is well described across the clinical literature. It also appears in approved combination products as a urinary antiseptic. The neuro claims rest on a different and much thinner body of work: low-dose methylene blue has been proposed as a metabolic enhancer with animal and mechanistic evidence for memory and neuroprotection, and reviewed as an emerging neuroprotective agent, with continuing preclinical delivery work. Reviews of that area consistently describe it as promising and early rather than established.

The unknown

Whether any cognitive effect exists at the doses people self-administer, and what chronic dosing does. The dose-response is genuinely non-linear in the underlying pharmacology, so the assumption that a small daily dose is simply a gentler version of the antidote dose is not safe.

Our read

A real drug doing real work in a narrow emergency indication, borrowed to support claims it has never been tested for. The interaction with serotonergic antidepressants is the part that matters most: this is a monoamine oxidase inhibitor, a very large number of people take an SSRI, and that combination has killed people. Approved for something is not approved for this.