Unfortunately many articles are behind paywalls.  Here are some that are free to read.  PNAS is a very high quality journal.<p>Proceedings of the National Academy of Sciences (PNAS):<p>Long-term effects of adolescent-onset and persistent use of cannabis
<a href="http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pmc&#x2F;articles&#x2F;PMC3479595&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pmc&#x2F;articles&#x2F;PMC3479595&#x2F;</a><p>Persistent cannabis users show neuropsychological decline from childhood to midlife
<a href="http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;22927402" rel="nofollow">http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;22927402</a><p>Personality may explain the association between cannabis use and neuropsychological impairment
<a href="http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;23460701" rel="nofollow">http:&#x2F;&#x2F;www.ncbi.nlm.nih.gov&#x2F;pubmed&#x2F;23460701</a>