Cannabis can leave teenagers three years behind their classmates, study finds

Regularly smoking cannabis can affect teenagers so severely that they end up three years behind their classmates in terms of brain development, a landmark study has found. The results of the investigation, which involved almost 4,000 secondary school children in Canada, led researchers to conclude cannabis is more toxic for youngsters' brains than alcohol. Persistent use of the drug seriously affected basic reasoning skills – while it also had a disastrous effect on self-control, they found. Meanwhile, a separate study has found hard evidence that the main psychoactive compound in cannabis, tetrahydrocannabinol (THC), causes changes in the brain that trigger schizophrenia. In the high school study, researchers at Montreal University studied pupils from the time they entered the Canadian seventh grade – aged 12 or 13 years – for four years.