http://www.wisegeek.org/what-is-mann...#didyouknowout

http://www.ohsu.edu/xd/research/cent...rs/therapy.cfm

you ever seen chemistry experiments where a semipermiable membrane tube is filled wih a sugar solution and then placed in a beaker of water and it swells up as osmosis occurs. that's the opposite of what mannitol is used for.

if it entered the brain it would be very dangerous, it would increase the pressure.

Mannitol is an osmotic diuretic. As such, it essentially draws water out of cells. It is used as a drug transporter because it can temporarily draw water out the BBB cells, thereby widening the openings and allowing certain chemicals/drugs to pass through. But mannitol itself is not permeable, so it doesn't pass through cell membranes like some other drugs that will pass through the BBB. If used in large amounts for a long period of time, small amounts of it may leak into the brain, but unlikely in dose controlling levels. It must be taken intravenously to be used as a BBB opener and drug transporter. Taken orally, the way Bluesking is using it, probably will have no effect at all on the BBB. It's a sweetener in low doses and a laxative in higher doses. But it always will be a diuretic, which is why I caution against using this on your own without medical advice.

I'm not going to post any more links to mannitol as I believe there have already been more than enough already.