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Young cannabis smokers run risk of lower IQ, report claims

28 August 2012 Last updated at 19:08 BST

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

The findings come from a study of about 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.

Mark Easton reports.