This just in, guys: being stoned throughout your teenage years might be bad for your brain. Shocking—we know.

A new study published in the journal Proceedings of the National Academy of Sciences looked at 1,037 New Zealand children from birth to age 38, administering an IQ test at 13, before ever smoking, then again at 38. Subjects answered questions about drug use at 18, 21, 26, 32 and 38 and nominated a close friend or family member to answer questions about their perception of the subject’s attention and memory.

Of the participants, about 5% started smoking marijuana as teens, and “those who smoked marijuana at least four times a week and used marijuana throughout their lives saw their IQ drop an average of 8 points,” writes LiveScience. “The drop was not explained by other drug use, years of education, schizophrenia or using marijuana the day before the test.”

Furthermore, “Quitting or reducing cannabis use did not appear to fully restore intellectual functioning among adolescent-onset former persistent cannabis users,” said Professor Terrie Moffitt, of KCL’s Institute of Psychiatry, who participated in the study.

Meaning, if you smoked all through high school but quit as an adult, the damage is done.

What is happening in a high school teen brain is still unclear, but Susan Tapert, a neuropsychologist at the University of California-San Diego, who was not part of the study, told LiveScience it may have something to do with the choices teen stoners make.

“What people tend to do when they’re under the influence is different than they would otherwise,” Tapert said.

For instance, pot users may be less inclined to attend classes or do other activities that give the brain a workout. Getting off track early on can also limit future opportunities and thereby reduce IQ, she said.

That said, people who started smoking as adults were able to bounce back from cognitive decline caused by smoking marijuana. The Telegraph reports:

The cognitive abilities of the 10 per cent of people who started in their 20s – who could loosely be classed as college smokers – also suffered while they were still smoking.

However, if they gave up at least a year before their IQ test at 38, their intelligence recovered, suggesting their brains were more resilient and bounced back.

The impact this type of study will have on legalization remains to be seen, but hopefully the negative impact of marijuana on young people’s lives will be weighed against the negative impact of a criminal record and jail time.

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