Did you know that cannabis can do this? “THC blocks an enzyme called acetylcholinesterase, which speeds the formation of amyloid plaque in the brains of people with Alzheimer's disease. The Alzheimer's drugs Aricept and Cognex work by blocking acetylcholinesterase. When tested at double the concentration of THC, Aricept blocked plaque formation only 22% as well as THC, and Cognex blocked plaque formation only 7% as well as THC.” From “Marijuana May Slow Alzheimer's” at WebMD.

But THC doesn't stop with "just" preventing the deposit of amyloid plaque in the brain! THC activates both the "get high" CB1 receptors, but also the healing CB2 receptors. (If you have no idea what I am talking about please read "Introduction to the Endocannnabinoid System" by NORML.)

“The activation of cannabinoid CB2 receptors stimulates in situ and in vitro beta-amyloid removal by human macrophages”, “Activation of the CB(2) receptor system reverses amyloid-induced memory deficiency” - both at PubMed, or the shorter news article, “Cannabinoids remove plaque-forming Alzheimer's proteins from brain cells”  (Medical X Press).    

(FYI- in situ means on the site, in this case in a brain; in vitro means in a test tube;  macrophages are your “clean up crew” cells.)