Is it true that marijuana really cause brain damage?

Maybe: The effects, if any, are not nearly so severe as the loss of the fine neuronal structure in chronic heavy drinkers that causes their well-known personality deterioration. I have no use for either -- life's too rich to be goofy or self-absorbed. But studies that show heavy weed-smokers to be less achievement-oriented hardly prove cause & effect, and measures of thinking ability seem mostly intact.