Is marijuana bad for your brain? - Anees Bahji

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In 1970, marijuana was classified as a schedule 1 drug in the United States: the strictest designation possible, meaning it was completely illegal and had no recognized medical uses. Today, marijuana's therapeutic benefits are widely acknowledged, but a growing recognition for its medical value doesn't answer the question: is recreational marijuana use bad for your brain? Anees Bahji investigates.

Lesson by Anees Bahji, directed by Anton Bogaty.

In 1970, marijuana was classified as a
schedule 1 drug in the United States:

the strictest designation possible,

meaning it was completely illegal and had
no recognized medical uses.

For decades, this view persisted

and set back research on the
drug's mechanisms and effects.

Today, marijuana’s therapeutic benefits
are widely acknowledged,

and some nations have legalized medical
use or are moving in that direction.

But a growing recognition for marijuana’s
medical value doesn’t answer the question:

is recreational marijuana use
bad for your brain?

Marijuana acts on the body’s
cannabinoid system,

which has receptors all over
the brain and body.

Molecules native to the body,
called endocannabinoids,

also act on these receptors.

We don’t totally understand the
cannabinoid system,

but it has one feature that provides
a big clue to its function.

Most neurotransmitters travel from
one neuron to the next

through a synapse to propagate a message.

But endocannabinoids travel
in the opposite direction.

When a message passes from the
one neuron to the next,

the receiving neuron releases
endocannabinoids.

Those endocannabinoids travel backward
to influence the sending neuron—

essentially giving it feedback from
the receiving neuron.

This leads scientists to believe that
the endocannabinoid system

serves primarily to modulate
other kinds of signals—

amplifying some and diminishing others.

Feedback from endocannabinoids slows
down rates of neural signaling.

That doesn’t necessarily mean it slows
down behavior or perception, though.

For example, slowing down a
signal that inhibits smell

could actually make smells more intense.

Marijuana contains two
main active compounds,

tetrahydrocannabinol or THC,
and cannabidiol, or CBD.

THC is thought to be primarily responsible
for marijuana’s psychoactive effects

on behavior, cognition, and perception,

while CBD is responsible for
the non-psychoactive effects.

Like endocannabinoids,

THC slows down signaling by binding
to cannabinoid receptors.

But it binds to receptors all over
this sprawling, diffuse system at once,

whereas endocannabinoids are
released in a specific place

in response to a specific stimulus.

This widespread activity coupled with
the fact that the cannabinoid system

indirectly affects many other systems

means that each person’s particular
brain chemistry, genetics,

and previous life experience largely
determine how they experience the drug.

That’s true much more so with marijuana
than with other drugs

that produce their effects through one
or a few specific pathways.

So the harmful effects, if any, vary
considerably from person to person.

And while we don’t know how
exactly how marijuana

produces specific harmful effects,

there are clear risk factors that
can increase peoples’ likelihood

of experiencing them.

The clearest risk factor is age.

In people younger than 25, cannabinoid
receptors are more concentrated

in the white matter than
in people over 25.

The white matter is involved in
communication,

learning, memory, and emotions.

Frequent marijuana use can disrupt
the development of white matter tracts,

and also affect the brain’s ability to
grow new connections.

This may damage long-term learning
ability and problem solving.

For now, it’s unclear how severe this
damage can be or whether it’s reversible.

And even among young people, the risk
is higher the younger someone is—

much higher for a 15 year old than a
22 year old, for instance.

Marijuana can also cause hallucinations
or paranoid delusions.

Known as marijuana-induced psychosis,

these symptoms usually subside
when a person stops using marijuana.

But in rare cases, psychosis
doesn’t subside,

instead unmasking a persistent
psychotic disorder.

A family history of psychotic disorders
like schizophrenia is the clearest,

though not the only,
risk factor for this effect.

Marijuana-induced psychosis is also
more common among young adults,

though it’s worth noting that
psychotic disorders

usually surface in this age range anyway.

What’s unclear in these cases
is whether the psychotic disorder

would have appeared without
marijuana use—

whether marijuana use triggers it early,

is a catalyst for a tipping point that
wouldn’t have been crossed otherwise,

or whether the reaction to
marijuana is merely an indication

of an underlying disorder.

In all likelihood, marijuana’s role varies
from person to person.

At any age, as with many other drugs,

the brain and body become less sensitive
to marijuana after repeated uses,

meaning it takes more to
achieve the same effects.

Fortunately, unlike many other drugs,

there’s no risk of fatal overdose
from marijuana,

and even heavy use doesn’t
lead to debilitating

or life-threatening withdrawal
symptoms if use stops.

There are more subtle forms of
marijuana withdrawal, though,

including sleep disturbances,
irritability, and depressed mood,

which pass within a few weeks
of stopping use.

So is marijuana bad for your brain?

It depends who you are.

But while some risk factors are easy to
identify, others aren’t well understood—

which means there’s still some possibility
of experiencing negative effects,

even if you don’t have any of
the known risk factors.