Methylene blue

In people, the trials are small and short. One low oral dose raised brain activity on MRI during attention and memory tasks and produced 7% more correct memory answers in 26 healthy adults [1]. In adults with claustrophobia, it helped fear extinction stick after a successful exposure session but seemed to make things worse after an unsuccessful one [2]. Added to standard treatment in 37 people with bipolar disorder, a higher dose eased leftover depression and anxiety but did not improve thinking [3].

The largest trial was negative. In 891 people with mild to moderate Alzheimer's disease, a related compound, LMTM, did not slow decline at either tested dose [4].

The aging case rests on cells and mice. Methylene blue delayed aging changes in human skin cells and lab-grown skin [5], but in the Interventions Testing Program it did not change median lifespan in mice of either sex, with only a small rise in maximum lifespan in females [6]. No study has tested whether it slows aging in people.

• Methylene blue is an FDA-approved prescription drug only for acquired methemoglobinemia, given by vein. Drops sold as supplements are not approved for any use, and their strength and purity vary.
• It strongly blocks the enzyme MAO A, so combined with SSRIs, SNRIs and other serotonergic drugs it can cause serotonin syndrome, which has been fatal.
• It can break down red blood cells in people with G6PD deficiency and is not for anyone who is pregnant or breastfeeding.
• It turns urine blue or green and can stain the mouth and skin. High doses can themselves cause methemoglobinemia.
• Long-term effects of daily low doses in healthy people have not been studied, so any use belongs with a physician who knows your medicines.