It’s a tale as old as time – or at least as old as the global prohibition of cannabis: cannabis makes you stupid. Over the decades, we have all been infiltrated by pop culture images of the goofy, slow-witted stoner. Furthermore, a series of research studies have purported to support the theory that weed appears to lower your IQ. But is this really the case? Is there true causation between cannabis use and lower intelligence, or is it simply an association that could just as easily be linked to other factors? Let’s find out.
Cannabis has been an essential part of medicinal and spiritual traditions for a number of cultures and societies around the world for thousands of years. In some cases, the plant would have been used for its therapeutic properties to treat a range of ailments; in others, its intoxicating powers would aid in spiritual practices. But while there are reports that ancient consumers “used hemp smoke to induce visions and oracular trances”, there is little evidence anywhere in history the drug was associated with stupidity. That is, until the mid-late 20th century.
The creation of a stereotype
While it’s hard to put a finger on the exact moment the stupid stoner stereotype really took off, it can likely be traced back to the 60s and 70s – and perhaps even earlier. By now, most people are familiar with “reefer madness” and other such campaigns that were designed to not only demonise cannabis, but also Black and other minority communities.
This was an effective strategy, kickstarted in the US, where lawmakers were able to cultivate an association between cannabis (or “marihuana”) and the fears of a largely prejudiced population of Black and Mexican citizens. Eventually, this demonisation spread to counter-culture groups such as “hippies” who were painted as lazy and stupid – again largely thanks to their incessant use of cannabis and other drugs. Around the same time (1969) US President Nixon announced the now infamous War on Drugs, categorising cannabis as a Schedule 1 substance with a high potential for abuse and “no medicinal value” – and we all know how well this evaluation has aged…
What does the research say?
Despite the origins of the ‘stupid stoner’ stereotype, a number of studies have appeared to uncover a link between cannabis use and lower levels of intelligence. Furthermore, we are often warned of the negative cognitive effects cannabis can have, particularly on the developing brain. Yet, it remains unclear whether cannabis itself is actually a cause of stupidity or if there could be other explanations for this association. Nevertheless, let’s take a closer look at what some of the most prominent studies could tell us.
In 2007, researchers in New Zealand conducted a study to “investigate the non-acute relationship between cannabis and cognitive function in a sample of adolescents with a continuum of cannabis use.” The study involved 70 participants, which included both cannabis users and non-users, who were asked to complete a number of tests designed to assess cognitive functioning. The researchers found that adolescents who were regular cannabis users (more than once a week) demonstrated significantly poorer performance on four measures of cognitive function reflecting attention, spatial working memory and learning.
The largest and longest-running study in this area, published in 2012, built on these findings. A total of 1,037 participants, who were tested at the age of 13 and 28, were included in the study by researchers at Duke University, North Carolina, US. They concluded that “persistent cannabis use was associated with neuropsychological declines broadly across domains of functioning, even after controlling for years of education.” Furthermore, they noted that cessation of cannabis use did not fully restore neuropsychological functioning among adolescent-onset consumers.
However, a follow-up study published the following year found that Duke’s research failed to account for a number of factors that could also have played a role in changes to cognitive development, including cigarette and alcohol use, mental illness, and socioeconomic status – not to mention the extremely small sample of heavy users (38 of them, to be precise). This acts as a reminder that association should not be mistaken for – or touted as – causation. While an association simply indicates that two phenomena occur together, it does not, like causation, prove that once causes the other to occur.
Nonetheless, even an association between cannabis and lower cognitive and IQ scores is enough to perpetuate the ‘stupid stoner’ stereotype. Luckily, not all the evidence supports this theory. More recently, a number of studies have again aimed to tackle this supposed link and have yielded different conclusions.
One study by University College London in 2014 assessed data from the Avon Longitudinal Study of Parents and Children (ALSPAC, also known as “Children of the 90s”) – a long-term study that follows the health of children born in and around Bristol, UK in 1991 and 1992 – to gain an insight into the effects of cannabis use on educational and intellectual performance.
Data from a total of 2,235 participants were included in the analysis. The participants had their IQ tested at the age of 8, and again at the age of 15 when each participant also completed a survey on cannabis use. The researchers found that, while cannabis use appeared to be associated with decreased intellectual performance, it was also highly correlated with other risky behaviours, including alcohol, tobacco, and other drug use – all of which could also have impacted intellectual performance. Having taken these behaviours into account, the researchers concluded that “they found there was no relationship between cannabis use and lower IQ at 15.”
In a press release that accompanied the initial publication of this study, one of the researchers noted: “this is a potentially important public health message- the belief that cannabis is particularly harmful may detract focus from and awareness of other potentially harmful behaviours.”
However, heavier cannabis use (at least 50 times by the age of 15) did appear to be associated with impaired educational abilities and lower exam results (3% lower) at age 16. Furthermore, the researchers noted some limitations to their research. For example, cannabis use was self-reported, which means that some use may have gone unrecorded. Furthermore, given the age of participants at the time of analysis, these results may not be representative of long-term cannabis use.
Nonetheless, a growing body of evidence is slowly shifting opinion on the assumed stupidity-inducing effects of cannabis: A 2004 study tested general intelligence, executive functioning, attention, memory and motor skills in twins – where one twin had been a cannabis user, and the other was a non-user. The researchers concluded that “the results indicate an absence of marked long-term residual effects of marijuana use on cognitive abilities.”
Let’s summarise: Does weed make you stupid?
As you can see from the research laid out in this article, answering this question isn’t as easy as we might hope. At best, current research indicates simply that there isn’t enough evidence to suggest that cannabis use directly affects our intelligence. Nonetheless, the vast majority of health professionals are united in their recommendation that cannabis – particularly when used recreationally – should be used responsibly and such use – unless medically necessary – should be avoided during adolescence when the brain is still developing.
However, one thing that is becoming increasingly clear is that cannabis users can no longer be convincingly defined by such lazy stereotypes. If the slow trend toward legalisation and acceptance of cannabis use has taught us anything, it’s that cannabis users come in all shapes and sizes. Sure, some of those shapes may be a little dim, but that can’t be an excuse for ignoring all of the intelligent, creative, and brilliant individuals who use cannabis for a wide range of reasons.