Cannabis, IQ and the law

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Media captionYoung cannabis smokers run risk of lower IQ, report claims

Here's my report on new research that suggests young people who smoke cannabis run the risk of a significant and irreversible reduction in their IQ. The findings come from a study of about 1,000 people in New Zealand.

Although cannabis is widely used in the UK, possession can lead to up to five years in jail. The research has been seized on by both sides of the debate over whether to legalise cannabis.