A new study showing that marijuana negatively affects the brain over time:

A world-first study has identified how cannabis can damage brain circuits to cause significant long-term damage…

New research reveals marijuana unnecessarily trims the connections that form these circuits [for short-term memory, impacting long-term memory], leading to gaps.

Read more: http://www.dailymail.co.uk/health/article-3786106/Why-cannabis-bad-World-study-identifies-exactly-drug-stunts-brain-development.html