New study finds pot smoking leads to lower IQ

That’s why they call it dope. A new study suggests teenagers who smoke a lot of pot could be doing permanent damage to their brains.

The decades-long study of 1,000 New Zealanders
seems to show if you smoke marijuana heavily as a teen, your IQ drops by about 8 points and that drop persists into adulthood even after you’ve quit.

“Those who started as teenagers had not by age 38 gone back to the kind of intellectual abilities that they had as primary school pupils,” Professor Terrie Moffitt, a lead researcher in the study tells CBS.

It probably comes as no surprise that heavy pot smokers have problems with memory, concentration and overall brainpower but this study indicates that the negative effects are more lasting if you started as a teenager. People who start smoking marijuana as adults do not experience the same lasting effects. There is no noticeable drop in IQ for them.

Earlier studies found a link between mental ability and pot smoking but did not establish any cause and effect relationship.

More than 1,000 study participants from New Zealand were tested for IQ at age 13 – likely before any significant marijuana use – and again at age 38. All were born in the town of Dunedin during a year-long span ending in 1973.

In addition to IQ tests, participants were given five interviews between ages 18 and 38, including questions related to their marijuana use. At age 18, 52 participants said they had become dependent on marijuana, meaning that they continued to use it despite its causing significant health, social or legal problems. Ninety-two others reported dependence starting at a later age.

The study comes as Washington state voters prepare to vote on a new initiative legalizing and regulating marijuana in the state.

The Associated Press contributed to this report