Does Smoking Marijuana Make You Stupid?

It’s a misconception that smoking marijuana makes you stupid or, in
other words, that marijuana causes your IQ to decline. While this
misconception has been around for a long time, studies from prestigious
institutions such as Duke
point out a correlation only serve to further scare off people who could
benefit from marijuana. The reality is that reputable studies show
little likelihood of a connection between smoking marijuana and a
decreased IQ, although they indicate other possible links to IQ

Recent Studies

Flaws in the Duke University study quickly came to light. For example,
the study’s findings were too preliminary to indicate a general truth,
as only 38 of the 1,037 study participants used marijuana to the point
that they were diagnosed as addicted. The study also did not account for
other possible

to IQ declines such as trauma, abuse, and healthy or unhealthy family
relationships. In fact, a follow-up
in 2012 pointed
out that the Duke University study made no attempt whatsoever to look at
the implications of factors such as socioeconomic status, alcohol use
and mental issues on IQ decline.

Two studies published in January 2016 indicate that there’s no
connection between IQ and smoking marijuana. One study examined 2,235
British children, aged 8 to
, while the other study
compared pairs of teenage American identical twins. One twin in each
pair smoked marijuana, while the other did not.

The twins study, which is actually a combination of two twins
, showed that
there was no noticeably different cognitive level between one twin and
the other. This held true no matter how heavy a cannabis smoker one twin
was. In order to qualify as a marijuana user, a twin had to have used
marijuana at least 30 times to date or every day for more than six
months. Both types of siblings, smokers and nonsmokers, lost an average
of four IQ points during the study. These results are powerful because
the DNA and similar upbringings of twins are a control for factors such
as socioeconomic status. Interestingly, the study points toward the
conclusion that middle-school children who are intellectually
under-challenged may be more likely to seek out marijuana. However, it’s
important to keep in mind that the twins self-reported their marijuana
use and IQ scores.

The study of British children controlled for extraneous factors and
showed that marijuana use prior to age 15 had no predictive effect on IQ
or educational performance. In this study, about 25 percent of the
children said they had tried marijuana at least one time, and almost 3.5
percent had used it 50 times or more. Those who used marijuana heavily
demonstrated lower IQ scores and poorer educational performance, but
after researchers controlled for other variables, the marijuana
association went away.

Positive Effects of Marijuana

These study results are good news because marijuana has proven to be
extremely helpful. For instance, it helps people better cope with pain
ranging from chronic pain to menstrual
It also helps control blood sugar and weight gain, and sparks creativity
in many people. It helps with anxiety and

and even with PTSD. In cancer patients, marijuana not only alleviates
pain, it increases

and combats

Negative Effects of Marijuana

As with any substance, marijuana does come with some negative effects.
People who smoke it may have respiratory issues such as wheezing and
chronic bronchitis. Marijuana smoke may also damage the lungs, and for
the above two reasons, many people who use marijuana every day choose
vaporizers or edibles.

Perception of Marijuana and IQ: Then vs. Now

In the United States in the 1980s and 1990s, anti-drug ads pointed to
so-called negative effects of marijuana: laziness, stupidity and lack of
good judgment. Whenever marijuana smokers were shown in movies, they
commonly took the form of incoherent stoners with endless appetites.
Perceptions are now changing, as marijuana gains legal and social
acceptance. For example, nearly 70 percent of Americans believe that
alcohol is more

to a person than marijuana is, and more Americans support widespread
legalization than are against it. Medical

is legal in about half of U.S. states, and marijuana use is legal to a
certain non-medical extent in several states as well. And, of course,
study after study shows that people need not worry about hurting their
IQ if they smoke marijuana.

What Does Lead to IQ Decline?

So, if marijuana doesn’t lead to IQ decline, what does? One answer may
come in the form of a mix of factors, such as socioeconomic status,
mental illness, alcohol, hard drugs and other influences touched on by
marijuana studies. For example, the British study indicated that teenage
marijuana users are more likely to have had problems in childhood and to
be cigarette and alcohol users.

Rather than decrease IQ, marijuana use for many people helps them
stretch their mental and physical muscles. For example, it makes them
happier and less anxious, putting them in a more creative mood. It
decreases their pain levels, enabling them to exercise when they
previously wouldn’t have been able to. In turn, that exercise promotes
blood circulation, and that’s great news for a healthy brain and a
healthy body. So, from one perspective, marijuana actually boosts
intelligence, albeit in an indirect way.


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