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 University that 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 declines.
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 connections to IQ declines such as trauma, abuse, and healthy or unhealthy family relationships. In fact, a follow-up study 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 16, 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 studies, 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 cramps. It also helps control blood sugar and weight gain, and sparks creativity in many people. It helps with anxiety and stress and even with PTSD. In cancer patients, marijuana not only alleviates pain, it increases appetite and combats nausea.
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 harmful to a person than marijuana is, and more Americans support widespread legalization than are against it. Medical marijuana 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.