Unfortunately many articles are behind paywalls. Here are some that are free to read. PNAS is a very high quality journal. Proceedings of the National Academ

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