Smoking cannabis may be especially harmful among teenagers who are under 18 years of age, but it may be relatively safe for ‘over-18 brains’, according to new research published in the Proceedings of the National Academy of Sciences.
The paper is based on a follow-up of more than 1,000 individuals since their birth to age 38. They were interviewed at certain ages to learn about their substance abuse habits, among other aspects, and two neuropsychological tests were conducted at ages 13 and 38.
The results showed that people that started smoking at an early age experienced a higher neuropsychological decline, with an IQ drop of 8 points on average. Also, giving up the habit at some point of their adult life didn’t seem to bring a significant improvement.
‘Collectively, these findings are consistent with speculation that cannabis use in adolescence, when the brain is undergoing critical development, may have neurotoxic effects,’ write the researchers.
‘This work took an amazing scientific effort,’ adds Prof Terrie Moffitt of King’s College London’s Institute of Psychiatry, and co-author of the study. ‘We followed almost 1,000 participants, we tested their mental abilities as kids before they ever tried cannabis, and we tested them again 25 years later after some participants became chronic users. Participants were frank about their substance abuse habits because they trust our confidentiality guarantee, and 96% of the original participants stuck with the study from 1972 to today.’
Photo: Wikimedia Commons
Madeline H. Meier, Avshalom Caspi, Antony Ambler, HonaLee Harrington, Renate Houts, Richard S. E. Keefe, Kay McDonald, Aimee Ward, Richie Poulton, & Terrie E. Moffitt (2012). Persistent cannabis users show neuropsychological decline from childhood to midlife Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1206820109
Effects of cannabis
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