Cannabis is arguably one of the oldest plants cultivated by humans. It’s been used for thousands of years for its medicinal properties. However, a significant stigma still surrounds the cannabis plant.

One pervasive notion is that cannabis use can lead to poor cognitive functioning in longterm users. Research studies have even pointed to a correlational relationship between cannabis use and reduced IQ scores.

But does cannabis really affect your IQ? Let’s take a look at the most recent research dissecting the link between cannabis and intelligence.

The Link Between Cannabis and Intelligence

The idea that using cannabis makes you dumb goes back a long way—from the many anti-drug PSAs of the 1980s and 90s to cannabis legislation opposition at the state and national levels.

More recently, cannabis opponents have pointed to a 2012 longitudinal study from Duke University. The researchers followed study participants from birth to age 38. In the participants’ teen years, the researchers conducted interviews and tests to assess cannabis use patterns, IQ, and executive functioning.

The major conclusion of the 2012 study was that cannabis use was associated with declines in cognitive functioning and IQ scores. However, a follow-up report in the same journal concluded that the authors of the original study did not control for several important confounding variables like mental illness, alcohol and tobacco use, and socioeconomic standing.

Cannabis is Not Associated with a Decline in Intelligence

Additional studies have since been published that also refute the link between cannabis and declining intelligence. In 2016, a study followed over 2,000 British teenagers and found no evidence that cannabis use predicted either lower IQ scores or educational performance.

Even more recently, a 2019 study compared cannabis use among pairs of identical twins and found little evidence for a causal effect of cannabis on intelligence. Instead, intelligence is much more likely to be affected by a complex combination of factors including your genetics, socioeconomic background, and peer group. Interestingly, these factors may also influence your likelihood to use cannabis.

However, in states like California with recreational cannabis laws, the cannabis market is more highly regulated than ever. This means that more vulnerable populations like teens are likely to have a harder time accessing cannabis.

Additionally, the cannabis that’s available in legal cannabis states is of higher quality. Mandatory cannabis lab testing ensures that all legally sold cannabis products are free from harmful contaminants like heavy metals and pesticides, which, with prolonged exposure, can result in real and significant cognitive and health defects.