Long-term marijuana use, especially when started during adolescence, has been found to decrease IQ, while also impairing cognitive function.

Since an increasing number of teens believe that regular cannabis use does not affect their health, they are starting to smoke at younger ages, and even smoking on a daily basis, thinking the drug is not addictive.

This common belief, however, was proven false in the current study which indicated that smoking marijuana has long-term effects on the brain.

Recent research, also from September, has demonstrated other negative outcomes result from cannabis, including pregnancy complications, such as preeclampsia, and an increase risk of testicular cancer.

Researchers in the current study gave more than 1,000 13 year olds neropsychological tests before they started using marijuana, and again during mid-adulthood after using, in order to determine whether there was a connection between constant cannabis use and a neurophyscological decline.

After subjects were re-tested at age 38, results showed that long-term use had a negative effect on intellectual functioning, especially if usage started during the teen years.

The more people became dependent on marijuana, the greater decline was seen in their IQ. They also showed to have a significant impairment across 5 different cognitive areas, especially executive function and processing speed.

This research was the first long-term prospective study that tested young teens before they even tried marijuana, and then after more than 20 years of use later, re-tested them.

Certain factors greatly contributed to the results, including:

  • the age a person began to smoke
  • the degree of cannabis use

The findings were also important because they ruled out pre-existing differences in IQ between heavy marijuana users and others.

Those who started smoking as a teenager had a greater reduction in their IQ than those who began in adulthood.

The results are concerning since reports in the last 5 years have shown that marijuana use is increasing among teens, while their perceived risk of harm from use is decreasing.

The results of this study support the idea that cannabis use may actually cause some of the neuropsychological deficits that regular cannabis smokers experience.

The findings will hopefully encourage adolescents to not use cannabis, after realizing that their previous ideas were false and there is a severe risk associated with this addictive drug.

Written by Sarah Glynn