Evidence is mounting that regular marijuana use increases the chance that a teenager will develop psychosis [4], a pattern of unusual thoughts or perceptions, such as believing the television is transmitting secret messages. It also increases the risk of developing schizophrenia [5], a disabling brain disorder that not only causes psychosis, but also problems concentrating and loss of emotional expression.
Links
[1] http://www.health.harvard.edu/blog/teens-who-smoke-pot-at-risk-for-later-schizophrenia-psychosis-201103071676
[2] http://www.rethinkpot.org/tags/teens
[3] http://www.rethinkpot.org/tags/schizophrenia
[4] http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0002520/
[5] http://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0001925/