Apparently, the answer is yes. (HT: Josh Wood) And worse, if you start young, it appears the brain is less able to regain the IQ points lost while smoking. We could have a discussion about the methodology used, and we should beware that correlation does not imply causation in an observational study such as this. Still, the findings are troubling giving the perception that marijuana is a safer alternative to smoking tobacco. Here is a taste of the article from The Telegraph:
Researchers found persistent users of the drug, who started smoking it at school, had lower IQ scores as adults.
They were also significantly more likely to have attention and memory problems in later life, than their peers who abstained.
Furthermore, those who started as teenagers and used it heavily, but quit as adults, did not regain their full mental powers, found academics at King’s College London and Duke University in the US.
They looked at data from over 1,000 people from Dunedin in New Zealand, who have been followed through their lives since being born in 1972 or 1973.
Participants were asked about cannabis usage when they were 18, 21, 26, 32 and 38. Their IQ was tested at 13 and 38. In addition, each nominated a close friend or family member, who was asked about attention and memory problems.
About one in 20 admitted to starting cannabis use before the age of 18, while a further one in 10 took up the habit in the early or mid 20s.
Professor Terrie Moffitt, of KCL’s Institute of Psychiatry, who contributed to the study, published in the journal Proceedings of the National Academy of Sciences, said “persistent users” who started as teenagers suffered a drop of eight IQ points at the age of 38, compared to when they were 13.
You can read the rest here.