There’s a brand new study out that proves that teenagers who routinely smoke marijuana end up with a long-term drop in their IQ. The study results are based on survey data from more than 1,000 people in New Zealand, everybody born in the town of Dunedin during a year-long span ending in 1973. In addition to IQ tests, the panel was interviewed five times between ages 18 and 38. They were also asked questions related to their marijuana use.

The researchers didn’t find an IQ drop in people who became frequent users after 18. That would imply that smoking marijuana is especially harmful to the developing brain, an idea that fits in with earlier research.

The study looked at how IQ scores changed between ages 13 and 38 in participants from New Zealand. Experts said the findings aren’t definitive, but that the study’s methods get around criticisms aimed at some earlier research.

“Parents should understand that their adolescents are particularly vulnerable,” said lead researcher Madeline Meier of Duke University. Young people “don’t think it’s risky,” said Staci Gruber, a researcher at the Harvard-affiliated MacLean Hospital in Belmont, Mass. Gruber, who didn’t participate in the new work, said the idea that marijuana harms the adolescent brain is “something we believe is very likely, “and the new finding of IQ declines warrants further investigation’.

Pot smoking is a pretty common drug of choice for American teens. In June the government reported that 23 percent of high school students said they’d recently smoked marijuana, making it more popular than cigarettes. Do you think that this recent study will make teens think twice before smoking a blunt or do they really just not care? Tell us your thoughts in the comments below!