Teens who routinely smoke marijuana risk a long-term drop in their IQ, says a study reported by the Associated Press. Researchers didn’t find the same IQ dip for people who became frequent users of pot after 18. The findings are not definitive, but they fit with earlier signs that the drug is especially harmful to the developing brain. “Parents should understand that their adolescents are particularly vulnerable,'” said lead researcher Madeline Meier of Duke University.
Study participants from New Zealand were tested for IQ at age 13, likely before any significant marijuana use, and again at age 38. A mental decline between the two ages was seen only in those who started regularly smoking pot before age 18. Richie Poulton of the University of Otago in New Zealand, a study co-author, said the research suggests staying away from marijuana until adulthood if possible. “For some it’s a legal issue,” he said, “but for me it’s a health issue.” Pot is the world’s most popular illegal drug, with up to 224 million users between 15 and 64 as of 2010, according to the United Nations. In the U.S., 23 percent of high school students said they’d recently smoked pot, making it more popular than cigarettes.