Does cannabis cause lower IQ?
For a long time, cannabis was associated with lower IQ and it was generally assumed that people become less intelligent because of it. This issue is incredibly complex, and we still don't know what impact cannabis has on human intelligence. However, studies are beginning to show that the existing correlation between cannabis use and intelligence may not be causal.
What is IQ?
IQ is an abbreviation for "intelligence quotient" and is a quantitative method of testing and evaluating human intelligence. Many consider it a controversial measure, but more on that later.
IQ is measured using a well-known IQ test. There are many different versions of the IQ test, and some are labeled differently. However, they are all quite standardized today. The IQ test can test abstract, logical, and verbal reasoning, as well as general knowledge and much more.
Approximately two-thirds of participants scored between 85 and 115 points, and about 2.5% of participants scored higher than 130 points or lower than 70 points.
What Does IQ Really Tell Us?
IQ is far from a purely intelligence metric, but it is examined through many different factors, of which very few directly speak about the basic functions of the human brain, but rather about various interacting physical and environmental factors. Intelligence itself is an intangible concept that is very difficult to measure.
IQ tests are a legitimate means of measuring a certain type of "academic intelligence", but they tell us little about social intelligence or creativity. Even when we rely on IQ, we can observe our own bias regarding related intelligence and culturally anchored values.
Moreover, the types of cognitive abilities that the IQ test asks about are largely dependent on environmental factors. Although this does not mean that IQ says nothing about intelligence - there is no reason why sociobiological interaction should not be intelligence - this value carries and maintains prejudices. For example, IQ tends to benefit those who created it - white middle-class men.
Studies show that differences in average scores between different ethnic groups are caused more by socioeconomic conditions than genetic factors. The rapid closing of gaps is clear evidence that these results are more due to environmental differences than innate differences. What does this tell us? IQ can be considered an indicator of a person's origin and intelligence.
Why is This Important?
It has long been claimed that especially cannabis use during adolescence reduces IQ over time. Many studies confirm this hypothesis. However, upon closer examination, it turned out that cannabis may not be the cause.
Does Cannabis Reduce IQ?
It has long been claimed that especially cannabis use during adolescence reduces IQ over time. Many studies confirm this hypothesis. However, upon closer examination, it turned out that cannabis may not be the cause.
- Evidence That Cannabis Reduces IQ
Cannabis use in youth and lower IQ seem to be related. In the Meier et al. study, 1,037 participants were tested for IQ at age 13 and again at age 38. Between these years, they were asked about cannabis use at ages 18, 21, 26, 32, and 38.
It was found that users presumed to have a "persistent" cannabis habit experienced a statistically significant IQ decline. Moreover, the decline was particularly noted in people who started using cannabis during adolescence. Most concerning was that stopping cannabis use - even for an extended period - did not reverse this decline. Cannabis was found to potentially have neurotoxic effects on the developing adolescent brain.
A long-term Power et al. study recently found that long-term cannabis use during adolescence is associated with an average IQ drop of two points. This study reviewed 2,875 scientific papers and ultimately conducted a meta-analysis of seven of them. These seven papers contained 808 cases and 5,308 controls. This is probably the most extensive long-term meta-analysis of cannabis's impact on IQ to date.
As in other studies, it was found that cannabis use during adolescence is associated with an IQ decline, most often with a change in verbal IQ.
Although this study showed a clear correlation between cannabis use and IQ decline, it cannot prove that cannabis is the cause of this decline. An important aspect of all scientific research: Correlation is not synonymous with causation.
There are many studies showing that the relationship between cannabis use and IQ decline does not necessarily mean that cannabis is the cause.