http://www.theweedblog.com/study-marijuana-use-not-associated-with-changes-in-brain-morphology/ Looks like the original study didn't control for alcohol. Another nail in the coffin for prohibition. Weed is definitely less harmful to your brain than alcohol.
Another example of correlation doesn't necessarily = causation. Measles vaccine=autism... http://forum.grasscity.com/index.php?/topic/1357118-Scotty%27s-first-grow
2 years ago i saw a dr at mental health .He had said marijuana will make my brain shrink.??like ?really thanks for the post's