Early-Onset, Regular Cannabis Use Is Linked to IQ Decline

A NIDA-supported 25-year study of 1,000 individuals suggests regular cannabis use that starts in adolescence strips away IQ.  Study participants who initiated weekly cannabis use before age 18 dropped IQ points in proportion to how long they persisted in using the drug, while nonusers gained a fraction of a point. “This study is important because we have precious little evidence on whether or not drug use leads to enduring changes in cognition,” says Dr. Steven Grant, chief of the Clinical Neurosciences Branch within NIDA’s Division of Clinical Neuroscience and Behavioral Research.  “The issue is critical, because at stake are the…