DMSA does not cross the blood brain barrier to any clinical degree. But using it in the wrong manner can allow mercury to go into the brain of its own accord.

mercury has no problems getting into the brain and only needs to be wildly mobilised by a chelating agent used in the wrong way to get there and other sensitive tissue.

The only way unfortunately to get mercury back out is by using something that can get in like alpha lipoic acid, cilantro etc. But again they must be used at the right time in the right manner. Because of their ability to cross over, they must be used much later in the programme after a person has already chelated out much of their blood/tissue mercury.