Regular cannabis users who start using the drug before the age of
15 perform worse on brain tests than those who start later,
according
to new research published in the June issue of the
British
Journal of Psychiatry.
Researchers from the Universidade Federal de
Sao Paulo say their study suggests that early cannabis use may have
more harmful effects on people’s cognitive functioning.
The researchers asked 104 chronic cannabis
users to take part in a series of neuropsychological tasks. These
tested their executive functioning, attention, perseverance,
ability to form abstract concepts, visual and motor skills, and
mental flexibility.
Of the 104 chronic cannabis users, 49 started
using the drug before the age of 15 (early-onset users). The
remaining 55 started using it after the age of 15 (late-onset
users). On average, the early-onset group had used cannabis for
10.9 years - equating to an estimated lifetime consumption of 6,790
joints each. The late-onset group had used cannabis for an average
of 8.7 years – equating to 5,160 joints each. Another 44 people who
did not use cannabis also took the tests, and acted as the control
group.
There were no differences in IQ between the
three groups. However, the early-onset group performed
significantly worse than the late-onset group and the control group
on tasks which tested their sustained attention, impulse control
and executive functioning. For example, in a card-sorting test, the
early-onset group made more errors than the control group (10 vs
6.44) and completed fewer categories (2.77 vs 3.5). There were no
significant differences in performance between the late-onset and
control groups.
Lead researcher Dr Maria Fontes said: “We
found that early-onset, but not late-onset, chronic cannabis users
had deficits in their cognitive functioning. We know that
adolescence is a period in which the brain appears to be
particularly vulnerable to the neurotoxic effects of cannabis.
Brain imaging studies have shown that the brain before the age of
15 is still developing and maturing, so exposure to cannabis during
this period may be more harmful and lead to lower mental
flexibility. It is possible people who start to use cannabis at a
later age may use different neural networks, and be able to
compensate for their cognitive deficits more than people who
started using cannabis at an earlier stage of brain
development.”
For further information, please
contact:
Liz Leicester
or Deborah Hart in the Communications
Department.
Telephone: 020 7235 2351 Extensions. 6298 or 6127
References:
Fontes MA, Bolla KI, Cunha PJ, Almeida PP, Jungerman F, Laranjeira RR, Bressan RA and Lacerda ALT. Cannabis use before age 15 and subsequent executive functioning. British Journal of Psychiatry 2011; 198:442-447