A recent neuroscience study from Harvard Medical School claims to have discovered brain differences between people who smoke marijuana and people who do not. Such well-intentioned and seemingly objective science is actually a new chapter in a politicized and bigoted history of drug science in the United States. Different-looking brains tell us literally nothing about who these people are, what their lives are like, why they do or do not use marijuana, or what effects marijuana has had on them.
Cannabis rots your brain — or does it? Last year, a paper published in Proceedings of the National Academy of Sciences (PNAS) suggested that people who used cannabis heavily as teenagers saw their IQs fall by middle age. But a study published today — also in PNAS — says that factors unrelated to cannabis use are to blame for the effect. Nature explores the competing claims. (See also: New Research Questions Marijuana’s Impact in Lowering IQ)
A 2012 Duke University study made international headlines purporting to find a link between heavy marijuana use and IQ decline among teenagers. Other researchers questioned the findings immediately: Columbia University's Carl Hart noted the very small sample of heavy users (38) in the study. A follow-up study published 6 months later in the same journal found that the Duke paper failed to account for a number of confounding factors. A new study from the University College of London provides even stronger evidence that the Duke findings were flawed.
Heavy marijuana use is associated with cognitive decline in about 5% of teens, according to a new study, which suggests that the heaviest users could lose 8 IQ points, according to a report, published in the Proceedings of the National Academy of Sciences. If the link is real, the effects on cognition could be dramatic. But intelligence and cognition is affected by a plethora of other factors, including genetic, social and environmental influences that may supersede any influence from drug use.
The President of the International Narcotics Control Board (INCB), Raymond Yans, has voiced grave concern about the outcome of recent referenda in the United States of America that would allow the non-medical use of cannabis by adults in the states of Colorado and Washington, and in some cities in the states of Michigan and Vermont. Mr. Yans stated that “these developments are in violation of the international drug control treaties, and pose a great threat to public health and the well-being of society far beyond those states”.