Marijuana does not lower IQ and can reverse cognitive decline, according to recent studies

Marijuana has been paraded as the drug that makes you dumb. This caricature is rapidly loosing merit in 21st century. Multiple studies attest that cannabis does not lower IQ and can bolster cognitive performance.

In the first study of its kind, scientists investigated the long-term effects of marijuana use in teens, comparing IQ fluctuations in twin siblings who either used or refrained from marijuana for 10 years. After taking various environmental factors into consideration, the scientists found no connection between marijuana use and a lower IQ.

“This is a very well-conducted study… and a welcome addition to the literature,” Valerie Curran, a psychopharmacologist at the University College London, told sources. Her colleagues deduced “broadly the same conclusions” in a separate non-twin study with more than 2,000 British teenagers published this month in the Journal of Psychopharmacology.

Twin studies navigate around hurdles of previous research

Previous studies that associated marijuana with cognitive decline, like memory loss and low IQ, only analyzed a “snapshot” in time, explained statistician Nicholas Jackson of the University of Southern California in Los Angeles, head author of the study. This makes it impossible to determine which came first: the drug use or the cognitive decline.

To navigate around these hurdles, scientists began investigating large groups of teenage drug use over time. The first study found a significant decline in IQ between the ages of 13 and 18 in heavy marijuana users than those who scarcely, if ever, used marijuana before the age of 18. However, the authors of the study acknowledged that they failed to consider other factors that may have lowered IQ, such as a teen’s family environment or whether they dropped out of school.


An effective way to address this problem is with identical twin studies. In the recent study, researchers reviewed 789 pairs of adolescent twins enrolled between the ages of 9 and 11. Over 10 years, the team administered five intelligence tests and confidential surveys about the use of marijuana, opioid painkillers, cocaine and binge drinking.

Although marijuana users lost about four IQ points, so too did their abstinent twin siblings. “Our findings lead us to believe that this ‘something else’ is related to something about the shared environment of the twins, which would include home, school, and peers,” Jackson said.

Furthermore, twins who reported daily marijuana use for six months or more did not show any change in their IQ compared to teens who tried marijuana fewer than 30 times. This is a “clear indication that cannabis is unlikely to be the cause of any IQ decline,” said Claire Mokryz, a Ph.D. student in Curran’s lab.

Marijuana cannabinoids repair and create new brain cells

In fact, other studies suggest that marijuana can actually boost cognitive performance. One of the latest discoveries about cannabinoids, a class of chemical compounds in marijuana, is their ability to act as an antioxidant in the brain.

According to German researchers, cannabinoids are capable of cleansing and repairing damaged brain cells. In addition, they increase the production of new brain cells, which contradicts years of conventional understanding about how the brain ticks. Furthermore, cannabinoids fuel mitochondria in the brain, the powerhouses of energy responsible for proper cell function.

These discoveries suggest that cannabinoids could be used to mitigate brain inflammation, which leads to cognitive decline, neural failure and brain degeneration. By providing these receptor sites with cannabinoids, patients may be able to treat and reverse brain disorders like Alzheimer’s disease, Parkinson’s disease and Huntington’s disease.

The medicinal benefits of marijuana continue to mount. However, the authors of the twin study do not encourage teenagers to smoke pot. “This does not mean that heavy use in adolescence is problem-free,” said Jackson. “We desperately need more research on the effects that marijuana has on the brain.”

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