It was really great for brain-fog. It's like the brain fog just disappeared after starting to take this stuff. I have/had other cognitive issues, those have also been helped somewhat by this stuff. One potential downside is that you may get a headache or brainfog if you stop taking this stuff for a couple of days. You will also get negative effects if you take too large a dose for you.
It's a dye to stain tissue and it's an old anti-malarial drug. Mostly it's available as a liquid and you dilute it down to the appropriate concentration and then take it.
There's a lot of discussion on this thread and other threads on the same forum:
http://www.longecity.org/forum/topic/23947-methylene-blue/
It delays cellular senescence and is mito-protective against oxidative stress and cadmium. At higher doses it's a MAO-I and at even higher doses it's an anti-malarial.
So you would want to keep the dose lowish in the "nootropic" range.
It seems the sicker someone is, the lower the dose they tolerate. So maybe start with 1mcg per dose and work your way up to a dose which helps. If you go too high it will cause a bit of brain fog, so you will know what a good dose is. The reason is that MB actually reduces efficiency of mitochondria, so if you have few working mitochondria, then a larger dose may worsen things.
The half-life is something like 5 hrs, so you have to dose multiple times a day. I use 750mcg x5/day, but i've been taking it for a while.