What does marijuana do…

What does marijuana do to the growing brain?

By AMIE THOMPSON • Tribune Staff Writer • May
30, 2010

An Allstate Insurance advertisement suggests that
teenagers are missing part of their brain.

And while any parent can probably say that is true,
Great Falls neurological surgeon Paul Gorsuch said
there is scientific evidence that shows that your
brain is not fully developed until you are in your
early 20s, usually around age 23.

“While the overall size of the brain does not change
much during adolescence, relative amounts of d
ifferent components, nerve connections, nerve
growth, and brain chemical transmitters are all
maturing,” Gorsuch said.

The frontal cortex of the brain is where all these
changes are happening. It’s the last brain region to
fully develop. This scientific evidence explains a lot
about teenager’s behaviors, because the frontal
cortex is responsible for executive functions
including logic, decision making, abstract
reasoning, evaluating options, weighing
probabilities and determining risks.

If you change the development of your frontal lobes,
it is likely those abilities you have will be
diminished from what you might have been, but
much has gone unproven, explained Gorsuch.

When a person smokes marijuana, the chemical
binds to special cannabanoid receptors, many of
which are in the frontal cortex of the brain.

When the drug locks to the receptor, it creates a
series of complex reactions.

“Any chemical that has an effect on our brain —
sugar, narcotics, nicotine, the cannabinoids in
marijuana, adrenaline — create that effect by
binding or docking to a receptor,” Gorsuch said. “In
the case of narcotics, one of the ultimate results is
that we may ‘feel’ less pain.”

Cannabanoid receptors are present in the body at
only 14 days gestation, which means they are
crucial for telling nerves where to go, what to make,

what to do and what to connect to, Gorsuch said.

“Basic science says that these are important in how
the brain develops,” he said.

Here is where the debate begins.

Scientists do not understand the role of
cannabanoid receptors in the development of the
frontal cortex connections.

“So what happens when you start stimulating those
cannabanoids (with marijuana) more than usual? In
terms of what it is doing at a molecular level, we
don’t know,” Gorsuch said.

Gorsuch said scientists do not fully understand how
the process is occurring, but “there are likely
‘critical windows’ of development when artificially
stimulating potent chemical receptors in the brain
may result in permanent brain changes.”

“It’s a big black box,” he added.

Many studies have been done, but the evidence is
still not scientific.

“All the evidence is showing a trend, but we don’t
know for sure,” Gorsuch said. “You can say that
there is evidence to not do it.”

Dr. John Stowers, who is an emergency room doctor
in Great Falls, also prescribes medical marijuana to

those patients he thinks the benefits outweigh the
risks. For teens, he said, it would be rare for it to be
worth the risks.

“Chronic, habitual use at a young age delays
maturity both mentally and socially,” Stowers said.

Since the early 1990s, functional MRIs have also
clued scientists in to what happens to a brain on
marijuana. One study compared two different
adolescent groups — one group did not use
marijuana and the other group were chronic
marijuana users who stopped for one month prior
to testing.

“While the marijuana group could complete the tasks
assigned, their overall thinking abilities were worse
and the functional MRI showed that they had to use
more of the parietal and frontal lobes of their brains
to accomplish the same task the non-users did with
less of their brain,” Gorsuch said.

“Or, as the author of the study put it, speaking of the
marijuana users, ‘Their brain is working harder that
is should,’” Gorsuch added.

Gorsuch also believes that addiction is “an
adolescent risk.”

He said teens are probably much more venerable of
becoming addicted than someone who makes it into
their 20s or 30s without becoming addicted to a
substance.

“It’s a much bigger risk,” he said.

Some will argue that only those who are prone to
addiction will become addicted.

“It’s a simplistic view to say that,” he said.

It comes back to nature versus nurture, and
Gorsuch said it’s more complicated than just one or
the other. It’s a mixture of probabilities.

What is known for sure is that for those genetically
predisposed to schizophrenia run a much higher
risk of developing the disease if they smoke
marijuana as an adolescent.

“One study has said that you are more than six times

more likely if you smoke it more than 50 times,”
Gorsuch said.

Other studies suggest that the risk is there even if it
doesn’t run in your family.

“Literature suggests there could be a potential factor
on its own,” Stowers said.

But the nature of the association between long-term
marijuana users and an increase in psychotic
illnesses has yet to be proven, Gorsuch added.

Stowers said he is careful not to prescribe medical
marijuana for anyone with a major psychiatric
history.

He said the mental health community in general do
not like using marijuana as a medicine, because “the
benefits don’t outweigh the risks.”