Research conducted in the United States, Australia, and New Zealand has provided evidence of a connection between marijuana use and depression.
• One 16-year study showed that individuals who were not depressed and then used
marijuana were four times more likely to be depressed at follow up.
• Another study investigated changes over a 14-year period and found that marijuana
use was a predictor of later major depressive disorder.
• Yet another study over a 21-year period found that marijuana use was associated
with depression, suicidal thoughts, and suicide attempts.
• A 2007 study of 3,239 Australian young adults from birth to age 21 found a
relationship between early initiation, and frequent use of cannabis and symptoms
of anxiety and depression, regardless of a personal or family history of mental illness.
