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