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In 2014, the United States Federal Bureau of Investigation (FBI) admitted that their strict employment policy, which prohibited past cannabis use within three years, made it difficult to find competent cybersecurity professionals. Cannabis consumers have long been plagued by a slothful, stupid stereotype, yet recent research suggests that there is no connection between cannabis and low IQ.

Does weed make you stupid?

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To start off, it’s important to note that research on how cannabis impacts the brain is mixed. No studies have been able to say conclusively that cannabis causes any changes in intelligence or IQ. Yet, no studies have been able to say with absolute certainty that it doesn’t affect intelligence, either.

What is certain is that in preclinical trials, cannabis compounds have encouraged the growth of new brain cells, not killed them. In the laboratory, cannabis compounds can promote the processes of neurogenesis, which is the growth of new neurons.

In adults, neurogenesis typically slows down with age. Should these preclinical trials hold true in human studies, cannabis may one day be a novel therapeutic tool in aging and brain care medicines.

However, until more substantial human research is completed, early investigations seek to rule out whether or not the herb can harm the brain. Thus far, results fall on both sides of the fence.

The biggest concern? Chronic cannabis consumption in adolescents, a topic which is discussed in greater detail below.

Regardless of the verdict, there are certainly a lot of highly successful and talented cannabis consumers out there. Folks who certainly would never earn the title of unintelligent. These include Whoopi Goldberg, Morgan Freeman, Carl Sagan, and Hunter S. Thompson.

The cons: research on cannabis and intelligence

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On the side of caution, a 2007 New Zealand study tested 70 adolescents. The participants abstained from cannabis for 12 hours before taking a series of cognitive tests. The those who identified as chronic cannabis consumers (more than once a week) scored worse on cognitive functioning tasks like attention, spatial working memory, and learning.

However, this observational article fails to determine whether or not cannabis is the cause of this change. At best, this shows an association between cannabis environments and cognitive difficulty.

Further, in the words of Dr. Frances Jensen, author of The Teenage Brain, adolescent brains “hold on” to cannabis compounds a lot longer than adult brains. This may mean that teens need more time to fully return to baseline after consuming cannabis.

Another study published in 2012 tested 1,307 individuals from birth to age 38. They found that chronic teen cannabis consumption correlated to an estimated loss of 6 IQ points, after controlling for confounding factors like tobacco, alcohol, and education.

The study pointed out, however, that these IQ changes did not occur in adult-onset cannabis consumers. Rather, the risk group was consistent with other research, chronic consumers who began prior to the age of 18. The study authors mention,

In fact, adult-onset cannabis users did not appear to experience IQ decline as a function of persistent cannabis use.

This is great news since recreational cannabis shops are open to adults 21 and over. In the Netherlands, patrons must be at least 18 to purchase the herb.

The 2012 study also received some criticism after publication. Some argued that this paper did not adequately rule out other reasons for the IQ decline, such as family environment or whether or not the participant had dropped out of school.

The pros: studies find no link

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While the above results may give parents pause about cannabis, not all large-scale studies have had this result. Unfortunately, this is where cannabis research turns into a game of he said, she said. While research shows some sort of association, several high-quality, recent studies have called bluff on some of the early reports.

For example, one major study found that adolescent cannabis use had no impact on the brain. Researchers followed 2,235 British teenagers and gave cognitive tests to those who had consumed cannabis by the age of 15. 24% of the group fessed up to trying the herb at this early age.

Those who consumed the plant less than 50 times did not differ from those who hand never consumed the herb in terms of IQ or educational performance. After adjusting for cigarette use, the researchers found that early tobacco consumption was associated with greater intellectual impairment.

This lead the authors to conclude that older research may have overestimated the cognitive impact of early cannabis use. The study was published in 2016 in the Journal of Psychopharmacology

Does cannabis lower your IQ?

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Recent studies suggest that cannabis does not lower IQ in the long term. However, there are several issues with using IQ as a test of intelligence. Unlike factors like height and weight, IQ and other psychological traits cannot be measured with exact precision.

IQ tests also measure reading comprehension, limits, series, and mathematic skills. However, they do not test other forms of intelligence, like creativity, emotional understanding, social skills, mechanical skills, or skills used while creating art.

Further, levels of education and socioeconomic status may greatly influence IQ. Lower socioeconomic status is associated with a greater variability in levels of intelligence, as measured by IQ.

Those from lower socioeconomic households are also more likely to consume cannabis more frequently. Overall, IQ tests are not adequate indications of a person’s overall ability.

Yet, IQ continues to be a standard measure of intelligence in scientific research. In 2016, scientists took another step forward in the cannabis and intelligence debate. A team lead by statistician Nicholas Jackson of the University of Southern California at Los Angeles tested the long-term effects of cannabis in twins.

Twin studies are a special treat in the science world. Identical twins share the exact same genetic makeup, meaning that scientists can rule out genetic differences and look directly at lifestyle and environment.

Jackson and his team recruited 789 identical twin pairs in two different locations, Los Angeles and in Minnesota. These twins shared upbringing and genetic makeup.

The twin pairs were then tracked over the course of 10 years, beginning in adolescence. Over the years, the researchers polled the teens about cannabis use and other drugs on five separate occasions. Participants also performed IQ tests.

At the 10-year mark, the scientists were able to compare cannabis-consuming twins with their abstinent counterparts. The research found that cannabis consumers did score an average of 4 IQ points lower than average, their non-consuming twins showed the same decline.

This lead the study authors to conclude that the drop in IQ points was not because of the cannabis itself, but rather due to,

[…] factors that underlie both marijuana initiation and low intellectual attainment.

Simply stated, there is something else in the environment of the cannabis-consuming twins that contributes to both cannabis use and intelligence. However, according to these twin studies, cannabis is not the cause of the IQ change. Jackson explains,

Our findings lead us to believe that this ‘something else’ is related to something about the shared environment of the twins, which would include home, school, and peers.

The study also found no difference in cognitive deterioration between teens who used cannabis daily for over six months and those who had just consumed on occasion. This adds to the evidence that cannabis may not cause IQ decline.

Bottom line? Whether or not cannabis causes changes to IQ is unconfirmed. However, as the earlier studies suggest, cutting out tobacco seems to improve the odds of staying healthy with the psychoactive plant.

Cannabis and creative intelligence

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Whole there is some debate over cannabis and its effect on IQ, the psychoactive herb has a reputation for boosting a different type of intelligence: creativity. Cannabis has long been a favorite herb among the artistic types.

Even renowned writer Maya Angelou enjoyed cannabis on occasion. She explains her favorite cannabis past time, Gather Together In My Name,

From a natural stiffness I melted into a grinning tolerance. Walking on the streets became high adventure, eating my mother’s huge dinners an opulent entertainment, and playing with my son was side-cracking hilarity. For the first time, life amused me….

Now, research is starting to show why cannabis and the artistic temperament seem to go hand-in-hand. Cannabis causes an increase of blood flow into the frontal lobe, a brain region responsible for cognitive thought and creativity.

Another study from 2012 found that in low doses, THC, the primary psychoactive in cannabis, may increase divergent thinking.

Divergent thinking is key to the creative process. It enables flexibility, originality, a splurge of new ideas. In high doses, however, THC may decrease divergent thinking below sober levels. Much more research on cannabis and creativity is needed to evaluate interpersonal differences and dosage issues.

Does cannabis ruin your memory?

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If memory is part of your definition of intelligence, then this is where cannabis may cause some issue. The herb does not affect long-term memory, or your ability to remember things that happened prior to consuming. Rather, the plant has acute effects on:

  • Spatial memory (finding your way around, remembering space and locations)
  • Working memory (remembering
  • Verbal memory (remembering words)

These acute effects are most pronounced within three hours of smoking the herb, or six hours after ingesting it. After the “high” wears off, the long half-life of THC can cause people to feel a little groggy or drowsy for a day or so after consuming. In teens, the groggy effects of cannabis may take longer to wear off.

With cannabis, you are likely to temporarily forget things like:

  • Where you put your keys/phone/wallet
  • Where you parked your car
  • The directions to a restaurant
  • What you were just saying
  • What you were just planning to do

In the long-term, however, things become more interesting. 2013 research published in Drug and Alcohol Review suggests that moderate to heavy cannabis consumption does not cause lasting changes to working memory. Yet, other research suggests that the herb may cause lasting changes to verbal memory.

A 2016 study suggests that chronic cannabis consumers may forget more words than their non-consuming counterparts. After following a group of 3,300 individuals for 25 years and gave them verbal and cognitive tests.

The researchers found that on average, half of all cannabis consumers could remember one word less than non-consumers in verbal memory tasks. They determined that the ability to remember one word is lost every five years of consumption.

Are a few words less enough to say that cannabis makes you stupid? That seems an awful lot like a matter of personal opinion.

Cannabis and chronic teen consumption

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Understandably, one of the biggest concerns about cannabis is the effect it has on the teenage brain. Cannabis now is more potent than ever in history, and medical researchers and parents are curious to know what affect the herb will have in the long-term.

When it comes to teens, it is better to wait. While several recent studies show that the herb is not associated with long-term changes in IQ, the herb can still have an impact on memory, which may make it difficult to retain information.

It can also disrupt sleep cycles, shortening time in REM sleep, the stage of the sleep cycle where memories are stored and filed. Larger impacts on the brain have yet to be determined.

There are also some concerns that early, chronic cannabis consumption can lead to impulsivity, attention, and behavioral problems. Though, long-term evidence has yet to prove this theory.

Legalization reduces teen cannabis use

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Keeping teens healthy is a great reason more states should consider the legalization and regulation of cannabis for adults. Surprisingly, cannabis legalization may actually make it more difficult for teenagers to get their hands on the herb.

National Survey on Drug Use and Heath published in 2016 found that after legalization, teen cannabis consumption dropped sharply in Colorado and Washington, the first two states to legalize, tax, and regulate recreational cannabis.

In 2013 to 2014, 20.81% of teens aged 12 to 17 had admitted to consuming cannabis. After recreational cannabis took hold, that number dropped to 18.35%. A similar pattern was found in Washington State, where the numbers dropped from 17.53 to 15.61%.

Other studies on the passage of medical cannabis laws have found no difference between teen usage rates in legal and non-legal cannabis states.

Allowing regulated, legal access to cannabis means fewer people buying the herb off of the streets, and more headed to shops where they have to flash their IDs for entry.

Does cannabis heal the brain?

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Almost all of the above research focused on whether or not cannabis causes harm to the brain. However, research over the past several years suggests that the herb may actually have some neuroprotective effects. Rather than killing brain cells, some preclinical research suggests that the plant may keep them from dying.

Back in 2013, rodent research conducted at the Tel Aviv University showed that administering an extremely small amount of THC within three to seven days after a brain injury can jumpstart biological processes that protect brain cells and improve long-term cognitive function.

The U.S. government is also interested in the healing properties of the cannabis plant. In the 90s, the American government filed a patent for the use of cannabinoids (cannabis compounds) as neuroprotective antioxidants.

The patent cites research that suggests that cannabinoids may limit the neurological damage of:

Where do I find more information on cannabis?

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Cannabis is a complex plant and it only continues to become more perplexing. While the herb may not make you stupid, it does interact with the body in unique and fascinating ways. To learn more about what cannabis does to the brain, check out these articles:

So, what’s the ultimate verdict? It’s too early to say just how exactly cannabis impacts intelligence. But, when used in moderation by adults, there is little evidence of long-term intellectual harm from this enticing plant.

Teens, however, should think twice before making the herb part of their lifestyle. Teens and youngsters with developing brains face the most risk when it comes to cannabis.

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