Before you say "Duh"

A new study out suggests that (medical) marijuana may not help to prevent cognitive decline or to lessen the accumulation of amyloid protein deposits in a mouse model for Alzheimer's disease.  Now, before you go crazy laughing and wondering why scientists do studies to find answers that anyone with a little common sense could give you, there is actually a precedent.  Marijuana acts in the brain on cells that express receptors usually attuned to molecules that the brain makes, called endocannabinoids (endogenous cannabis-like molecules).  Now, endocannabinoids have been shown to help keep brain cells alive under "stress" (stress being a catchall term for conditions known to kill nerve cells), and a compound called HU210, which activates cannabinoid receptors much more potently than marijuana had been shown in previous studies using rats to have some efficacy in keeping neurons alive under the types of "stress" the brains of Alzheimer's patients experience.  What I like best about this study is that it shows how science gives you answers even when they're not what you want to hear:

"As scientists, we begin every study hoping to be able to confirm beneficial effects of potential therapies, and we hoped to confirm this for the use of medical marijuana in treating Alzheimer's disease," says Song, a member of the Brain Research Centre at UBC and VCH Research Institute and Director of Townsend Family Laboratories at UBC.

"But we didn't see any benefit at all. Instead, our study pointed to some detrimental effects." 

So, if previous studies showed some benefit, but this one showed no benefit, which ones should we believe?  Well, obviously, more studies should be conducted, preferably on humans... I might just know some people who would volunteer to be studied.