Do
you know that marijuana is the most commonly used psychotropic drug in the
United States, right after alcohol? Numbers show that in 2018,
11.8 million young adults in the U.S. reported marijuana use in the past year.
The use of marijuana is more common in men than in women. Even though cannabis
consumption keeps increasing, most people are not aware of all the effects this
plant has on the brain. In this post, we discuss what effects marijuana could
have on brain health with long-term use. Are there any risks? Scroll down to
find out.
Short-term
effects of marijuana
We’re
going to start with a brief rundown of short-term effects on brain and body
associated with marijuana use. They include:
·
Impaired memory
·
Lower anxiety
·
Disrupted motor control
·
Bigger appetite
·
Faster heart rate
·
Sleep pattern changes
·
Decreased pain
How
marijuana affects cognitive functions long-term?
Despite
the ever-growing use of marijuana, the effects of long-term use are still not
thoroughly elucidated. The reason is simple; a vast majority of studies on
cannabis focused on short-term effects and results that people can experience.
However,
some long-term effects of marijuana are short-term carry-over effects.
Why
does that happen?
The
body fat attracts THC, the psychoactive cannabinoid responsible for the “high”
effect. Since the cellular walls in the body are comprised of fat, it’s easy
for cells to absorb THC. What happens next is that THC is re-released gradually
over a certain period of time.
If
you’ve ever wondered how a person can test positive for marijuana even when not
using it for several days now, you know the reason. Traces of THC persist in
the body for up to a month after you stop smoking. This also explains why some
short-term effects of marijuana use may last for a while.
Before
you start thinking this is just a theory, it’s worth noting the scientific
evidence confirms it. For example, a study from the Addictive Behaviors showed that people do
experience some effects of marijuana for a while even after they stop using it.
The main objective of this cross-sectional study was to examine relationships
between recent and past cannabis use on neurocognitive functioning.
For
this purpose, the scientists enrolled 158 subjects into the study. Of these, 68
participants were recent users, 41 were past users, and 49 subjects were
non-users. Past users were those who haven’t used marijuana for more than 28
days or four weeks.
Results
showed that recent marijuana users demonstrated significantly
worse attention and working memory performance than non-users. Their
information processing speed and executive functioning were also worse than in
people who have never used marijuana. Interestingly, there was no
statistically significant difference between recent and
past cannabis users in terms of neurocognitive
performance.
Although
cognitive functions were the worst in recent marijuana users, past
users performed more poorly on measures of executive function than non-users.
This implies that the effects of cannabis on the brain don’t
go away once a person stops using it; they remain for a while.
These
findings dictate that as long as you have THC in the body, marijuana will
continue to affect the brain.
While
it’s evident that marijuana can impair cognitive functions, the effects
on the brain itself and its structure and functions need more
attention and further investigation. This subject is not totally clear, but
several studies have inspected it, and we’re going to discuss their findings
below.
Long-term
effects of marijuana on the brain
As the
rates of marijuana use increase, so do the questions about its influence on the
brain. The research mostly focuses on short-term effects, as mentioned above,
but studies on the long-term impact of cannabis are emerging, and we can expect
even more of them in the future.
A study from the Proceedings of the
National Academy of Sciences (PNAS) found that marijuana use can
change brain structures, but further longitudinal study approaches are necessary
to uncover more on this subject. The research included 110 participants, of
which 62 were non-users, and 48 people were cannabis users. Marijuana users
were enrolled in the study if they currently use marijuana regularly at least
four times a week over the last six months.
The
findings showed that heavy, chronic marijuana users have lower orbitofrontal
cortex (OFC) gray matter volume compared to their counterparts who don’t use
cannabis. The orbitofrontal cortex is the area of a prefrontal cortex that sits
above the eye sockets. It is located at the front of your brain. This part of
the brain has extensive connections with sensory areas and limbic system
structures that are involved in memory and emotion. The OFC also receives
information about the sight of the objects.
The
effects of marijuana use on OFC aren’t as shocking if we bear in mind that OFC
is the main area in the reward network. Moreover, OFC is abundant in
cannabinoid receptor CB1, and it’s significantly implicated in addictive
behaviors. Since CB1 receptors, which are a part of the endocannabinoid system,
are positioned on excitatory terminals of cortical projection neurons, then
downregulation of these receptors negatively affects the plasticity of OFC.
While scientists couldn’t identify all the mechanisms through which marijuana
use decreases OFC gray matter volumes, they theorize it could be down to
changes in cell size, neuronal loss, and reduction in CB1 density.
In
other words, the PNAS study confirms the unfavorable effect of marijuana on OFC
connectivity but also emphasizes the complexity of this problem. You see,
greater functional connectivity of OFC was linked to an earlier age of onset of
regular use, while chronic marijuana use led to slower connectivity. This
relationship only paints a picture of how complicated the effects of marijuana
on the brain really are. Although some evidence shows that CB1 receptor
down-regulation may return to normal values with marijuana abstinence,
scientists concluded that more research is needed to confirm that.
Evidence
also shows that marijuana
use can affect white matter, and the younger a person is when he
starts smoking cannabis, the greater the damage. This study showed that
marijuana use had no impact on cortical volumes.
The
journal PLoS One published a study which found that
morphological brain alterations are observed in adults and adolescents who use
marijuana. These alterations are especially pronounced in the medial temporal
and frontal cortices and cerebellum. The effects are associated with the amount
of exposure to cannabis.
When
we’re talking about brain volume and cannabis use, it’s important to mention
that evidence shows people
with psychosis are more prone to these changes. However, the impact of
marijuana on the brains of people with psychological problems and risks
of psychosis should be further elucidated.
However,
not all studies on this subject agree that marijuana is responsible for brain
changes. For instance, the JAMA Psychiatry published
a study which showed that exposure to marijuana was related to smaller changes
in the left amygdala and right ventral striatum volumes. That being said, these
changes weren’t that significant. They were within normal variations,
scientists explain. This led the scientists to conclude that differences in
amygdala volume in marijuana users could be attributed to common factors
ranging from genetic to environmental origin. The causal influence (of cannabis
use on changes in amygdala volume) has little support.
Just
a reminder, the amygdala is an important part of the brain, and it plays a key
role in emotion and behavior.
Brain
development changes with marijuana
Human
brain changes and develops throughout life, but it is the most malleable in a
period between birth and the 21st birthday. Since many teenagers start smoking
marijuana and continue to do so well into adulthood, it’s impossible not to
wonder how cannabis affects developing brains. A study from the Brain journal
attempted to answer that question.
A
team of researchers compared MRI scans of subjects who have started using
marijuana in adolescence with the scans of participants who have never used
cannabis. In marijuana users, the neural connections between the
right and left brain hemispheres were decreased. This finding means that
internal communication in the brains of marijuana users is lower
than in non-users.
Despite
the importance of the study and its results, you still need to keep in mind a
few things. Like a vast majority of studies on the effects of cannabis, this
one also doesn’t show what happens when a person stops using marijuana for a
certain period of time. In other words, this research doesn’t show whether
internal communication in the brain improves once a long-time marijuana user
decides to stop. Some impairments could have been in the brain before marijuana
use in the first place.
On
that note, another study found
that people who started using cannabis in their adolescent years had lower IQs
in their 30s compared to childhood. The frequent cannabis use is associated with
a loss of six to eight IQ points measured in mid-adulthood.
The
greatest drop in cognitive performance was among people who started using
marijuana the youngest and who smoked most heavily. The weak cognitive
performance was independent of their socioeconomic status and other parameters.
Interestingly, this study showed that abstaining from marijuana doesn’t fully
restore neuropsychological functioning. In other words, those subjects didn’t
restore the lost IQ points after abstaining from marijuana.
Another piece of evidence shows that young marijuana
users experience a significant decline in verbal ability and general
knowledge between the preteen years and late adolescence or early adulthood. That
being said, those who started using cannabis at an older age already had low
scores at the beginning of the study. More precisely, they had low scores on
the brain functions even before they started using cannabis.
Can
long-term marijuana use harm my brain?
The
influence of marijuana use on the brain is a subject of many studies, but many
of them have conflicting results. Several studies have shown that marijuana
can, indeed, affect cognitive performance and induce some structural changes in
the brain.
But,
this doesn’t mean marijuana can destroy the brain entirely.
Long-term
and heavy cannabis usage (e.g., from adolescence to adulthood) can slow down
the brain, but won’t scramble it.
The
negative effects of marijuana on the brain are more pronounced in adolescent
cannabis smokers who continue using it into adulthood.
A
lot more studies are necessary to determine just how much marijuana use can
impair the brain’s functions.
One
of the greatest obstacles that prevent scientists from learning all the short-
and long-term effects of marijuana on the brain is that study
participants often use multiple substances.
Data about the participants’ health and mental functioning before the study is
limited. This also doesn’t allow scientists to take a look at the broader
picture. Changes in brain and cognitive functions can occur due to a wide range
of reasons, including another illicit drug, but without enough data, it’s
difficult for scientists to rule out other potential factors.
How
marijuana affects memory?
As
seen throughout this post, marijuana can have a significant impact on brain
function and cognitive abilities, including memory.
But
have you ever wondered why smoking marijuana could impair your memory and make
you forgetful?
Memory
impairment from cannabis happens because THC changes the way the hippocampus
processes information. Don’t forget that the hippocampus is an area of the
brain responsible for the formation of memory.
As
you age, the number of neurons in the hippocampus decreases. As a result, it
becomes more difficult to learn and store new information. Chronic exposure to
THC could accelerate the age-related loss of neurons in the hippocampus. In
turn, this area of the brain can’t form memory properly.
Conclusion
In
this post, we discussed the long-term effects of marijuana use on the brain.
Evidence on this subject is still conflicting, but scientists agree that early
onset of marijuana use can induce structural changes in the brain and lower IQ
scores. A lot more research is necessary to learn more about this subject.
References
https://www.drugabuse.gov/publications/research-reports/marijuana/what-scope-marijuana-use-in-united-states
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4032061/
https://www.pnas.org/content/111/47/16913.full
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4925620/
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0055821
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3474956/
https://pubmed.ncbi.nlm.nih.gov/26308883/
https://pubmed.ncbi.nlm.nih.gov/22669080/
https://pubmed.ncbi.nlm.nih.gov/22927402/
https://www.pnas.org/content/113/5/E500
https://www.drugabuse.gov/publications/research-reports/marijuana/what-are-marijuanas-long-term-effects-brain
https://www.drugabuse.gov/publications/research-reports/marijuana/what-scope-marijuana-use-in-united-states
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4032061/
https://www.pnas.org/content/111/47/16913.full
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4925620/
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0055821
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3474956/
https://pubmed.ncbi.nlm.nih.gov/26308883/
https://pubmed.ncbi.nlm.nih.gov/22669080/
https://pubmed.ncbi.nlm.nih.gov/22927402/
https://www.pnas.org/content/113/5/E500
https://www.drugabuse.gov/publications/research-reports/marijuana/what-are-marijuanas-long-term-effects-brain
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