Does marijuana use make you less smart?

Yes- if you start routinely using the drug before the age of 18. That's the conclusion of a new study published in the journal of the National Academy of Sciences.

The study finds that intelligence, attention and memory are all negatively impacted by dependent drug use for those under 18.

The longitudinal study looked at New Zealanders from age 13 to 38. IQ points dropped in only those study participants who started smoking before age 18.

The average IQ drop recorded was about 8 points. Given the average IQ is 100, an 8-point drop represents means a person goes from being in the 50th percentile for intelligence, to the 29th percentile.

Guest:

Madeline Meier, is a psychologist at Duke University. She's the study's lead researcher.