As dozens of states move toward legalizing marijuana—for both medical and recreational purposes—scientists and parents have asked what the impact might be on children. Will more teens use pot? Will doing so cause behavioral problems? Will they develop a substance-use disorder? According to a study published last month in the journal Addiction: yes, probably not and maybe. "Parents ought to be somewhat reassured that cannabis use doesn't lead to the type of mental health problems related to conduct issues," said Dan Romer, a co-author of the study [...]