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.

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