Teens who smoke marijuana could become less intelligent as an adult with irreversible effects, a new study suggests.
Researchers at Duke University measured the IQs of 13-year-olds before marijuana use. They then measured their IQs at the age of 38, after years of smoking.
They found intelligence levels declined by an average of eight points.
The study also found people who started smoking pot as adults did not suffer any decline in intelligence.
Researchers say the brains of teenagers are not fully developed and are more at risk to the adverse impacts of marijuana.
(CNN Contributed to this report.)