Everybody Must Get Stoned?

This is a startling result and I have to wonder why it isn't being more widely publicised:

In the present study, we observed smaller brain weights and volumes in male macaque monkeys after 1.5–2.3 years of exposure to marijuana at plasma drug levels comparable to those in treated humans. Exposure to marijuana was associated with a similar reduction in mean fresh brain weight, as well as mean fresh weight and volume of the left cerebrum, compared to matched, placebo-exposed animals. For both drugs, the magnitude of these effects was in the range of 8–11%. The reduction seemed to be global (ie including all brain regions), but was most robust in the frontal and parietal lobes. In addition, both gray and white matter volumes appeared to be reduced to a similar degree.