Effects of Cannabis on Teens: Studies Find No Drop in IQ


For the last few decades there have been numerous anti-drug campaigns that have put out the message that weed makes you stupid. Yet, the effects of cannabis have only begun to be researched and understood. For many years the use of marijuana by adolescents and young adults has been associated to a drop in IQ. This argument was backed up by a study of the effects of cannabis on teens and young adults, performed at Duke University in 2012. Since then, that study has received criticism by other researchers because it failed to take many other factors into account, including socioeconomic status, mental illness, and cigarette and alcohol use. This study has now been challenged and it seems that the effects of cannabis on teens does not include a decline in IQ or educational performance.

Two Studies That Challenged Supposed Effects of Cannabis

Many flower children breathe a collective sigh of relief.

Two new reports have surfaced that thoroughly study the effects of cannabis in very specific ways. One study followed a pair of American twins in which one of the twins smoked marijuana while the other did not. The twins were monitored for a period of ten years. Their environment, genetics, and socioeconomic status were the same, allowing the research to be a powerful window into the effects of cannabis. The research showed there was no decline in the IQ of the twin who smoked pot and that twin experienced no more cognitive deficits.

The other study focused on 2,235 teens from the U.K. aged between 16 and 18 years. The study factored in a variety of influencing aspects such as mental health, usage of other substances, and maternal health. The results determined that the use of marijuana at the age of 15 does not lower the IQ or educational performance ultimately concluding that the effects of marijuana on teenagers are not related to cognitive impairment.

Relieving Revelations

Approximately half of Americans smoke marijuana or have smoked it at some point in the past. The most common time for people to smoke marijuana is during teenage years or young adulthood. For the people who smoked during these years, it will be relieving to know that their IQ was not affected and cognitive functions are still intact as supported by these studies.

Other Findings Taken from the British Study

More research is still required to determine the full scope of cannabis’ effects on the brain.

The British study focused on the effects of moderate marijuana use. Other researchers have found that while the IQ does not decline after heavy use, there is a risk of other negative outcomes. It seems that heavy or excessive marijuana use can increase the risk of developing psychosis or even suicidal thoughts. While the IQ is not lowered by smoking cigarettes, the British study linked the relationship of cigarette smoking with poor educational performance. Other researchers have also come to this conclusion.

In general, teens and young adults who smoke marijuana will not decrease their IQ or general intelligence regardless of whether their use is moderate or heavy. The effects of cannabis seem relatively safe for teenagers as long as the use is not too heavy or excessive. Even prolonged use over a number of years did not produce any cognitive deficits. Our understanding of the effects of cannabis can only be increased through further study.


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