BBC News 28 August 2012 Last updated at 08:35 ET Share this pageEmail Print Share this page

Young cannabis smokers run risk of lower IQ, report claimsComments (842) By Dominic Huges

Health correspondent

Young people who smoke cannabis for years run the risk of a significant and irreversible reduction in their IQ, research suggests.

The findings come from a study of around 1,000 people in New Zealand.

An international team found those who started using cannabis below the age of 18 - while their brains were still developing - suffered a drop in IQ.

A UK expert said the research might explain why people who use the drug often seem to under-achieve.

For more than 20 years researchers have followed the lives of a group of people from Dunedin in New Zealand.

They assessed them as children - before any of them had started using cannabis - and then re-interviewed them repeatedly, up to the age of 38.

Having taken into account other factors such as alcohol or tobacco dependency or other drug use, as well the number of years spent in education, they found that those who persistently used cannabis - smoking it at least four times a week year after year through their teens, 20s and, in some cases, their 30s - suffered a decline in their IQ.The more that people smoked, the greater the loss in IQ.


The effect was most marked in those who started smoking cannabis as adolescents.

For example, researchers found that individuals who started using cannabis in adolescence and then carried on using it for years showed an average eight-point IQ decline.

Stopping or reducing cannabis use failed to fully restore the lost IQ.

Rad more @ http://www.bbc.co.uk/news/health-19372456

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