"Teenagers who regularly smoke cannabis are putting themselves at risk of permanently damaging their intelligence, according to a landmark study.
Researchers found persistent users of the drug, who started smoking it at school, had lower IQ scores as adults.
They were also significantly more likely to have attention and memory problems in later life, than their peers who abstained.
Furthermore, those who started as teenagers and used it heavily, but quit as adults, did not regain their full mental powers, found academics at King’s College London and Duke University in the US.
They looked at data from over 1,000 people from Dunedin in New Zealand, who have been followed through their lives since being born in 1972 or 1973. "
Based upon this evidence, use of legal pot should be restricted to those over 21 yrs-over 25yrs would be better still.