Marijuana: Not So Bad After All?

Researchers have shown again and again that abusers of the happy smoke drop out of school at higher rates than their peers.

What's been harder to show, however, is why this happens. The prevailing theory is that marijuana impairs memory and/or motivation, which lowers the desire and/or ability to stay in school.

But what if that's not how it works? That's what Daniel F. McCaffrey, Rosalie Liccardo Pacula, Bing Han, and Phyllis Ellickson of the Rand Corporation propose.

Obtaining data on some 4,500 South Dakotan seventh graders who were tracked through their expected graduation dates, the researchers attempted to piece apart other possible explanations for the link between marijuana use and higher dropout rates. These include a person's "predisposition toward problem behavior, use of substances other than marijuana, peer and family social influences, attachment to conventional institutions such as family, school and religion, emotional distress," and innate preference for enjoying life now as opposed to later. (The students were asked about these things in annual surveys.)

While the researchers first confirm that students who used weed three or more times in a month had a 600 percent higher chance of dropping out, that percentage is cut in half when the above alternative explanations are taken into account.

More surprisingly, when researchers also factored in the frequency of cigarette use, the chance of dropping out from smoking marijuana was no longer statistically significant. (On the other hand, looking at the frequency of alcohol use instead didn't change the probability of dropping out.)

What's going on here? There is little to no evidence that cigarette use by itself should hurt brain power or motivation, so controlling for it shouldn't have changed the chance of dropping out. The likely culprit is that there are some characteristics of marijuana smokers that exist before users start toking up frequently, and that these characteristics weren't properly accounted for. In economic parlance, there was an omitted variable bias. So what's been omitted? The researchers believe that peer or family influences are more likely to be the main drivers of higher dropout rates among marijuana smokers.

There are some caveats though. The study only covers South Dakota, which is quite rural, so other locales might not have the same results. Second, the findings are based on survey data which can be riddled with lies. (But it would be odd for students to tell the truth about smoking marijuana while lying about other seemingly more inane topics.) And lastly, as compelling pieces of evidence as Snoop Dogg and Willie Nelson might be, the findings don't prove that marijuana doesn't hurt brain functioning.