Controversy around the effect of cannabis smoking on the adolescent brain has been ongoing. A study following teenagers using drugs over time was first conducted in New Zealand, 2012. The study concluded that there was a significant decline in IQ of heavy cannabis users between the ages of 13 and 38. More recently, scientists studied identical twins over ten years, with one using and one abstaining, and found no link between marijuana use and lower IQ.
A study of identical twins from the same environment using and abstaining shows no link between marijuana use and a lower IQ.
Science mag follows the discussion between scientists on the controversial issue of cannabis lowering teenagers’ IQ. Scientist Valerie Curran praised the study on twins. She said it was very well conducted. She and her colleagues did a similar study on 2000 British adolescents and came to a very similar conclusion.
Nicholas Jackson, author of the twin study and statistician at University of Southern California, says most studies on the negative influence of marijuana on cognitive abilities such as IQ or memory loss focus on single incidences in time. It then becomes very difficult to determine if drug use or poor cognitive performance came first.
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Warning: it doesn’t prove it is safe for teenagers to use marijuana
George Patton, psychiatric epidemiologist from Melbourne University warns this does not prove it is safe for teenagers to use marijuana on a regular basis. He was also co-author of the earlier study done in 2012 in New Zealand. Critics of the study he co-authored claimed there was no way to show other external factors such as family, environment or dropping out of school didn’t cause the lowered IQ.
This is why Jackson decided to study identical twins. They come from the same gene pool and upbringing. He and his team looked at 789 pairs of twins from two different locations, California and Minnesota, between the ages of 9 and 11-years, over a time span of 10 years. The teenagers completed five intelligence tests and responded to surveys about their use of marijuana. Other drugs such as opioids, alcohol and cocaine were also covered.
Twin IQ’s stay twin if they use pot or not
Marijuana users lost four IQ points in the course of the study, but twins abstaining lost the same number of IQ points. Jackson drew the conclusion that the loss of mental sharpness was due to some other factor, such as family life, school, or peer stresses.
There were no differences in IQ changes in teenagers who smoked pot for six months or longer in comparison to those who used cannabis less than 30 times. A Ph.D. student in Curran’s team says this clearly indicates cannabis is not likely to cause IQ decline.
Why would a 13-year old want to get labeled for life?
Patton argues the new study has flaws. Information on how often and what quantity of cannabis was consumed is lacking, and the two groups received different surveys. He argues that the Los Angeles group’s investigation was not thorough enough. Jackson responded by saying it was unlikely for a 13-year-old who has only tried one puff of marijuana to take the chance of replying “yes” to the question “Have you ever tried marijuana?” as he could be labeled for the rest of his life. Patton says the new study doesn’t cut it as a means of debunking the findings he and his colleagues made.
Jackson said that although there is more and more evidence showing cannabis does not lower the IQ of adolescents using it, it does not mean heavy use is problem-free, as other abilities could very well be affected. He says more research is desperately needed to see what effect cannabis has on the brain. The best way to study the effects would be to give it to individuals and then observe how duration, dose and frequency affect cognition. But for now, such studies are ruled out by federal restrictions and ethical concerns.
More importantly why would teenagers seek refuge in drugs?
Jackson says that what is of more concern to him is what can possibly be wrong in the world of a 14-year old that they would seek refuge in drugs. One could speculate on a lot of causes, not least the trauma of puberty with its mood-swings and depression, but once again, the matter has not been investigated sufficiently to know for sure.
Primary source: http://www.sciencemag.org/news/2016/01/twins-study-finds-no-evidence-marijuana-lowers-iq-teens