There has been a good deal of interest in a question about whether very early adolescent heavy cannabis use may cause ongoing problems even when someone stops cannabis use.  The early teens are a time of rapid brain development involving those parts involved in emotional control.  Studies in rats have suggested large doses of cannabinoids (the active ingredients in cannabis) may alter longer terms patterns of anxiety.  Other studies in humans have raised a question about early cannabis users have reduced intelligence later in adulthood.  We found that in our study of two thousand young Victorians a two-fold higher rate of anxiety problems in the later twenties even where an individual was no longer using cannabis.  We could not account for it by other aspects of an individual’s lifestyle or their earlier history of mental health problems.  It is consistent with a view that heavy (at least weekly) early teen cannabis use does increase the risks for later anxiety problems.

Degenhardt L, Coffey C, Romaniuk H, Swift W, Carlin JB, Hall WD, Patton GC. The persistence of the association between adolescent cannabis use and common mental disorders into young adulthood. Addiction. 2013; 108(1): 124-33.