I would think it probably does cross the blood-brain barrier, since it is a small molecule. Also, for about 3 weeks of my initial Miracle-Mineral-Supplement cleanse, I had a lot of brain fog, which I would think had to do with the Miracle-Mineral-Supplement acting directly on the brain. The brain fog went away while I was still taking Miracle-Mineral-Supplement , so I assume whatever it was got cleaned out.