With the
legalization of recreational marijuana in Washington and Colorado, questions
about cannabis have vaulted into the public consciousness.
For a couple
minutes, let’s put aside policy concerns and look just at the effects of
cannabis in the brain.
Two studies published in top journals, both in April
2014, look inside human brains at the long-term effects of cannabis use. Is
cannabis addictive? Is it safe? Let’s consider the evidence.
First, an article in the Journal of
Neuroscience used MRI scans to look inside the brains of young,
recreational marijuana users at regions associated with addiction. Previous
studies have shown that other drugs known to be addictive affect the brain’s
reward centers – especially the brain’s amygdala, which controls emotional learning, and a structure called the nucleus accumbens, which controls pleasure (including our
ability to laugh).
We’ve also known that adding cannabis-based chemicals to the
brains of rats creates changes in these structures related to addiction. But
it’s quite a leap from introducing cannabinoids to rat brains and knowing the
effects of smoking pot on humans.
So a team of
Harvard-led researchers recruited 40 young adults – 20 marijuana users and 20
non-users – to see if what is true in the brains of rats is also true in the
brains of college students. Sure enough, human marijuana users had changes in
volume, density and topography in both of the amygdala and nucleus accumbens.
“These data suggest that marijuana exposure, even in young recreational
users, is associated with exposure-dependent alterations of the neural matrix
of core reward structures,” the researchers write.
This study
and the studies that lead up to it show that marijuana use creates physical
changes in the brain associated with addiction. And, the researchers point out,
these results were seen in non-dependent, young adult users. What are the
effects of even heavier pot use on the brain?
That’s the
question of the second study, published in the Nature journal, Neuropsychopharmacology. Again, the
study used MRI imaging to ask if the effects of cannabis-based chemicals seen
in rat brains are also seen in human brains. This time the study compared heavy
marijuana smokers to occasional smokers to see if overall brain changes are
more extreme, the more you smoke. And it looked outside just the structures of
addiction to explore changes in overall brain structures: how does marijuana
use affect the brain?
The study
found reduced grey matter volume in nearly all brain regions that are rich in
the “receptors” that can trap and respond to cannabis-based chemicals. These regions
include a long list of structures, almost all of which are part of a network
that controls motivation, emotion, and emotional learning. Here’s an important
part: the degree to which these brain areas changed was due to one of two things
– either heavy use or starting use during adolescence. Long-term heavy users
had the same reductions in grey matter volumes as lighter users who started in
their teens.
So let’s
revisit our two questions. Is marijuana addictive? Yes, we can see it as a
real, visible change in the brain’s reward system. And is marijuana safe? No,
and the younger you start or the more you use over time, the more dangerous it
is to your brain. Whether or not you believe recreational marijuana should be
legal, it’s time to admit its power as a dangerous, addictive drug.
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Richard
Taite is founder and CEO of Cliffside Malibu, offering evidence-based,
individualized addiction treatment based on the Stages of Change model. He is
also co-author with Constance Scharff of the book Ending
Addiction for Good.
