“Only dopes use dope.”
This anti-drug slogan from the 1980’s sought to drive home the myth that using marijuana decreases your intelligence. Since that time, this argument remains one of the main reasons that people fear marijuana legalization. Never mind that some of the most intelligent people in history, Carl Sagan, Steve Jobs. Bill Gates, even Barack Obama, used marijuana, the idea that marijuana makes you stupid has been hard to shake.
A recent study published in the journal of Neuroscience makes the claim that casual marijuana use may be linked to changes in brain structure. This study, based on a sample of 20 people, became fodder for the media claims such as: Even Casually Smoking Marijuana Can Change Your Brain, Study Says, and Recreational Pot Use Harmful to Young People's Brains. However, in their rush to confirm the myth around marijuana and stupidity, those reporting the story left out some very important details.
As previously mentioned, the study was conducted on 20 marijuana users, and 20 controls (non-users). Only healthy marijuana users were selected for the study, eliminating those with any physical or mental health problems.
What this means is, different brains or not, these were healthy people by definition. Even the brain structure differences did not result in illness or disability compared to their non-using peers. There are, of course, other issues with the study design, such as the way “casual use” was defined. As pointed out by fellow scientist Lior Pachter, a few of the participants were using 10 joints per week, and one was using 30 per week, above what most would consider “casual use.”
Secondly, brain changes are not the same as cognitive deficits. This study looked at brain imaging only, not at actual problems experienced by the participants, nor did it give the participants any kind of cognitive assessment above and beyond the shape of their brains. Men and women’s brains also differ in structure, but one would never then assume that one gender is somehow disabled by these differences.
Finally, as with much of the research on drug use, there is confusion over correlation and causation. While this study can claim that “casual” marijuana is use associated with varying brain structures, they CANNOT say that these differences were caused by marijuana use.
John Gever, at MedPage Today, provided an excellent analysis of this reporting inaccuracy. As Gever points out:
“Breiter (one of the authors) claims that this study, ‘raises a strong challenge to the idea that casual marijuana use isn't associated with bad consequences.’ Um, no, it doesn't -- not without before-and-after MRI scans showing brain structure changes in users that differ from nonusers and documentation of functional impairments associated with those changes.”
So, what’s the bottom line? As we move towards marijuana regulation, rather than prohibition, research on the impacts of marijuana use and policies on public and individual health are essential.
However, if future policies are to be truly evidence based, we need to be careful about the accuracy and honesty with which we present the findings.
Amanda Reiman is a policy manager for the Drug Policy Alliance.