A new report by the White House Office of National Drug Control Policy will claim that use of marijuana by teens can lead to dependency and mental illness.
Oh brother, he we go again.
In science, there is a thing about causality that is tough, if not impossible to demonstrate, especially when it comes to human behavior. To establish a cause of behavior, one must show: 1) a correlation; 2) temporal order; and 3) a lack of spuriousness.
A correlation is simply an association or relationship. In the case of marijuana use and bad outcomes like dependency and mental illness, showing a correlation is simple; one must only show that as one factor changes so too does the other. For example, see the following slide from the AP news story reported by Yahoo News titled "Feds: Teen use of pot can lead to dependency, mental illness."
The quote above suggests a correlation, or a relationship, between marijuana and depression. This simply means that marijuana use and depression are related.
Yet, to establish a cause and effect relationship between marijuana use and depression, scientists would have to also demonstrate temporal order. This means that if marijuana use causes depression (or any other bad outcome), marijuana use must occur before the bad outcome. If the bad outcome comes before marijuana use, then marijuana use obviously cannot be the cause of the bad outcome (but the bad outcome might be the cause of the marijuana use).
If you just sat down and thought about it, which is more logical? Is it more logical to assert that smoking marijuana may make you depressed? Or is it more logical to expect that feeling depressed might make one feel like smoking marijuana (which could be seen as a form of self-medication for people who feel down)?
The latter is more logical to me. Yet, the Office of National Drug Control Policy (ONDCP) will suggest that it is the other way around.
ONDCP will also assert that marijuana use makes one more likely to commit suicide, as shown in the following slide:
This leads us to the issue of a lack of spuriousness. A spurious relationship is a false relationship. In the social sciences -- even after a correlation and temporal order have been established -- scholars must try to determine if any other factors might account for the relationship between one factor (e.g., marijuana use) and another (e.g., suicidal thoughts). That is, they must be able to rule out other factors that might account for both outcomes.
So, ask yourself one simple question: What other factor could explain marijuana use by teens and suicidal thoughts. What else could account for why a young person might smoke pot and also have thoughts of killing oneself, making it look like marijuana use leads to suicidal thoughts, when in fact it is a third factor?
How about depression? The following slide from the news story implicates it may be depression that is the real issue here, since depressed kids are more likely to smoke pot in order to feel better, and they are apparently more likely to become "dependent" on the drug, as well:
If depression is the issue, a war on pot will do nothing to alleviate the true problem.
And surely, there are other factors involved, too. In fact, science has identified factors unique to individuals, their families, peer groups, neighborhoods, schools, and so forth, that may account for why some kids (a small minority) use marijuana and experience bad outcomes while others (the vast majority) do not. This slide from the news story suggests just that:
So, why doesn't ONDCP just tell the truth? Given what we know about ONDCP, you'd be foolish to expect them to do so.
The truth is that marijuana is a relatively harmless drug. That is, relative to the vast majority of drugs out there (including alcohol, tobacco, and prescription drugs available in most kids' parents' medicine cabinets), marijuana is a very safe drug.
The truth is that only a very small group of young people and adults who use the drug may experience bad outcomes.
The truth is that the vast majority of people who use the drug have literally no bad (lasting) outcomes. Instead, they use the drug in mostly recreational contexts in pro social ways and have positive experiences.
Perhaps the folks at Yahoo News who created the web site about the story about this issue had these truths in mind when they created this slide:
Now, that doesn't look so bad, does it?
When ONDCP issues its report, stand up and be heard. Tell them to report the truth instead of making more (false) scary claims about marijuana.
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Matthew Robinson is Professor of Criminal Justice and Criminology at Appalachian State University. He is the author of nine books, including Lies, Damned Lies, and Drug War Statistics (SUNY Press, 2007).