Adolescents most at risk of brain damage from long term, heavy cannabis use

9 August 2012

Long term, heavy cannabis use is harmful to the developing brain, according to new research conducted at the Murdoch Childrens Research Institute.

The study, which was published in the leading neurology journal, Brain, found individuals who were heavy cannabis users, who had used for a long period of time, had significant changes in their brains - specifically the areas of brain which connected regions involved in memory function.

Importantly, it also found that the age at which regular cannabis use first began was a key factor in determining the severity of any deterioration in the brain.  This study showed the younger you were when you started, the worse the outcome.  Those who started in early adolescence suffered the greatest abnormalities, and experienced greatest cognitive impairment.  

Researchers studied 59 cannabis users with longstanding histories of heavy use and compared this to 33 non cannabis users.  They used magnetic resonance imaging (MRI) images and sophisticated connectivity techniques to identify what areas of the brain were affected. 

Lead researcher, Doctor Marc Seal, from Murdoch Childrens, said their findings indicate that that there are critical periods of brain development and ages at which the brain is more vulnerable to damage from regular cannabis use. 

"Our results suggest that long-term cannabis use is hazardous to white matter in the developing brain.  This was especially true for those who had started in adolescence, as we know the brain is still developing during this time."

"Given the association between cannabis-related harms and age of onset of regular use, delaying use may minimise such harmful effects."

Researchers say the connectivity disturbances they saw in the study, particularly in the hippocampus and commissural fibres, may underlie the memory impairment and other cognitive deficits that are observed in long-term heavy cannabis users.      

White matter brain alternations have been associated with various functional and clinical outcomes in schizophrenia.

In the study the most common age which people started using cannabis was 16 years old, and most had been smoking for about 15 years.  This is the largest study to comprehensively investigate brain white matter and its changes among individuals with a history of longstanding, heavy cannabis use. 

The study was undertaken in conjunction with the University of Melbourne and University of Wollongong.