Marijuana Smokers Have IQ Permanently Reduced, Study Asserts

Recently published research from New Zealand asserts that people who begin using cannabis before their eighteenth birthday suffer an average eight-point IQ decline if they continue using the drug into adulthood.

The study followed about 1,000 participants from childhood up until the age of 38 and was based off of a series of interviews conducted with each individual. During each meeting, the participants' mental abilities were tested, allowing for several points of reference.

During adolescence "The brain produces loads of synapses, probably more than it needs, then it starts cutting down, making them more efficient," says University College London researcher Dr. Anne-Lisa Goddings.  

As a result, the brain is still undergoing formative development in the years before they are legally considered adults.

The study states, "Persistent cannabis use over 20 years was associated with neurophysiological decline, and greater decline was evident for more persistent users."

"Collectively, these findings are consistent with speculation that cannabis use in adolescence, when the brain is undergoing critical development, may have neurotoxic effects," the study adds.

Goddings reiterates that the adult brain is relatively fixed, and argues that the adolescent brain is more susceptible to the effects of cannabis.

Professor Terrie Moffitt of King's College London states that "It is of course part of folk-lore among young people that heavy users of cannabis...seem to gradually lose their abilities and end up achieving much less than one would have anticipated. This study provides one explanation as to why this might be the case."

While the study's results are far from definitive, Moffitt expressed that the results may change the way that we think about cannabis from here on out.

Professor Val Curran of the British Association for Psychopharmacology weighs in one what this study means: "What it shows is if you are a really heavy stoner there is going to be consequences, which I think most people would accept...This is not occasional or recreation use."

"You would probably find the same thing in heavy drinking. We should not put cannabis on a pedestal," he concludes.