A new study says that marijuana may hurt the developing brain by decreasing the IQ of teens who use the drug. Researchers looked at the IQ scores of 1,000 people between the ages of 13 and 38, discovering that IQ dropped an average of 8 points among youths who smoked pot from their teen years into adulthood. Marijuana did not seem to affect the IQ of people who started smoking after reaching adulthood. “The brain is undergoing important developmental changes during adolescence,” said lead researcher Madeline Meier of Duke University. “And it seems like marijuana can disrupt these critical changes.” Although this is one of the first studies to track the same marijuana users over a long period of time, its results are consistent with other studies that found marijuana producing negative effects during the teen years. Meier cautions that any attempt to legalize marijuana should still place restrictions on teen use. Two states are currently considering ballot initiatives to legalize marijuana for recreational use after age 21.