Teenagers who smoke cannabis and/or electronic cigarettes containing nicotine seem more likely to have poor school marks and engage in risky sexual behaviour, a new study suggests. “We have seen that young people who vape electronic cigarettes, use cannabis or do both are more likely to have poor school grades, report difficulties with concentration and doing their work because of physical, emotional and psychological problems,” said study co-author Dr. Nicholas Chadi, a pediatrician and clinical researcher specializing in adolescent medicine and addiction at Ste-Justine Hospital.