Scientists have found that the area at the front of the brain, known as the orbitofrontal cortex, which controls memory, reward and decision- making, is six per cent smaller in children who go on to smoke cannabis compared with those who do not.

This difference in size may mean the brain is not as effective, so children with a smaller orbitofrontal cortex could be more impulsive and less capable of carefully calculated decision-making…

Previous research has found that adults who are heavy cannabis smokers have much smaller brain volumes in this area, but it had, until now, been assumed the damage was caused by the regular drug use.