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The number of teenagers smoking marijuana has increased dramatically compared to the number of teenagers smoking cigarettes, as per a recent survey done in the US. But smoking weed as a teenager can damage the IQ and cause memory and attention problems.

Recent reports have shown that adolescents are starting using pot at younger ages and many of them smoke it on a regular basis. Teenagers believe that smoking marijuana is less harmful than smoking cigarettes and hence, more and more of them are making the switch from cigarettes to weed.

A scientific proof on the long term impact of smoking weed

A new study, published in the August issue of the journal Proceedings of the National Academy of Sciences, was taken up in order to find the long term impact of smoking weed on the neuropsychological health of the concerned individuals.

In the largest study of its kind, more than 1000 individuals born in the New Zealand city of Dunedin, in 1973, were followed up till the age of 38. All the participants of the study underwent an IQ test at the age of 13 and again at the age of 38. They were subjected to different psychological tests to assess their memory, power of reasoning, ability to visually process a piece of information, and the processing speed, when they reached the age of 38.

The participants were also questioned five times regarding marijuana usage between the ages of 18 and 38. The relatives of the participants and other people knowing them were also quizzed about the marijuana dependency of the participants and any noticeable memory and attention problems in them.

The researchers found that by the time the participants reached the age of 18, 52 had already become dependent upon marijuana. 92 other participants became dependent upon marijuana at a later stage of the study. In what can be termed as a significant finding, the researchers noticed a fall in the IQ levels of participants who had started smoking weed before the age of 18. Those participants who were found marijuana dependent in three or more surveys had a drop of almost 8 points compared to their IQ in the initial survey done at the age of 13. In other words, their IQ levels had dropped from being in the 50th percentile to being in the 29th percentile.

This drop in the IQ was permanent, i.e. it didn’t improved even if the participant had given up on weed by the time he reached the age of 38.

This decline in IQ was not observed in the participants who did not smoke weed until they were adults with fully developed brains.

The participants who smoked marijuana at least once a week for a minimum of one year, also showed a similar decline in their IQ levels. This damage to IQ was not found to be associated with the amount of weed consumed at one go or its potency.

The fall in IQ level cannot be underestimated as it affects various aspects of a person’s life, starting from his education to his income and overall quality of life.

Continue reading after recommendations

  • “Persistent cannabis users show neuropsychological decline from childhood to midlife”, by Madeline H. Meier, et al, Published in the August 27, 2012 issue of the Journal PNAS, accessed on September 20, 2012.
  • “Teens who smoke pot can damage memory, intelligence”, by Kate Kelland, published in the August 27, 2012 issue of Reuters Health, accessed on September 20, 2012.
  • “National Study: Teen “Heavy” Marijuana Use Up 80 Percent Since 2008, One in Ten Teens Reports Using Marijuana at Least 20 Times a Month”, by Cassie Goldberg, published on May 1, 2012 at The Partnership at, accessed on September 20, 2012.
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