Blog of Rights

Government Marijuana Scare Stories Deliberately Confuse Correlation with Causation

By Jag Davies, Drug Law Reform Project at 3:05pm

If you've read the news the past two weeks, you may have noticed eye-grabbing headlines with bold proclamations that marijuana use leads to increased risk of heart disease and that teens who use marijuana suffer from greater rates of depression. If you took the time to read these so-called "studies," however, you know that they are fear-mongering government propaganda pieces meant to stand in for science. Unfortunately, with a few exceptions — like David Harsanyi's column in the Denver Post — much of the media has simply parroted the government's press releases.

Let's start with "Teen Marijuana Use Worsens Depression: An Analysis of Recent Data Shows 'Self-Medicating' Could Actually Make Things Worse," a seven-page "report" mostly filled with bar graphs and empty space, prepared by the Office of National Drug Control Policy (ONDCP). It's never a good sign when you've got to use "Could Actually" in the title of a report.

As usual, the government's deceptive claims are based on the deliberate confusion of correlation with causation. As criminology professor Matthew Robinson, Ph.D, explains in his analysis of ONDCP's latest report, credible social science must demonstrate both temporal order and a lack of spuriousness to make a claim of causality. In other words, scientists have to consider the order in which things take place as well as other variables that could be responsible for an outcome prior to concluding that one phenomenon causes another. ONDCP's report ignores temporal order by failing to account for whether marijuana use occurs as a result of depression, or vice versa. Worse, the report doesn't take into account other variables that might account for both outcomes — such as family environment, peer groups, use of other drugs, etc. As Victor Reus, a psychiatrist at the University of California, explained, "Both conditions could be related to something else. Depressed teens are more likely to exercise less, stay indoors and watch TV. Take your pick as to which one is causal."

Media accounts of ONDCP's teen marijuana-depression report omit mention of larger, more credible studies that present evidence to the contrary. For example, in April 2008, a British government advisory panel concluded that there is no conclusive evidence of "a causal relationship between the use of cannabis and the development of any affective disorder." Meanwhile, in November 2007, the American Medical Association's peer-reviewed journal, Archives of Pediatrics & Adolescent Medicine, published a comprehensive study of 5,263 students finding that teens who have used marijuana demonstrate the same rates of psychosocial problems as those who have never used marijuana.

Next, let's take a brief look at the study that prompted the bold Reuters headline, "Marijuana May Up Heart Attack, Stroke Risk." First of all, the study only examines a scientifically insignificant sample of 18 marijuana users, who smoke "78 to 350 marijuana cigarettes per week" — 11 to 50 joints per day. While we don't know precisely what fraction of the roughly 20 million Americans who have used marijuana in the past month smoke at least 11 joints a day, needless to say it is a miniscule fraction.

Even more ludicrous, the study doesn't even evaluate whether any of these extreme marijuana smokers actually have an increased risk of mortality. The study simply found that heavy marijuana users showed increased blood levels of a particular protein called apolipoprotein C-III that is involved in the body's metabolism of triglycerides, but didn't examine whether these users were more likely to develop heart disease.

Again, this study flies in the face of larger, more credible studies. A 2001 study published in the Journal of Public Health Nutrition that examined approximately 11,000 marijuana users and non-users found that marijuana smokers' nutritional health was equal to that of non-smokers. Another 2001 study published in the journal Circulation examining the association between heart attacks and marijuana use in 3,882 heart attack sufferers found negligible risks — about the equivalent of the risk of vigorous exercise for someone of average fitness. A 1999 British Heart Foundation study even found that marijuana-like compounds play a key role in reducing high blood pressure, suggesting that marijuana could be a useful treatment for hypertension. And then of course there's Dr. Donald Tashkin's authoritative 2006 study finding that even heavy marijuana users are not at increased risk for lung cancer, contrary to government claims.

Still, don't expect the government's half-baked attempts to demonize marijuana to end soon — they're the product of the confluence of several institutionalized interests. First, there is the need to justify arresting 830,000 people on marijuana charges each year (89 percent for mere possession). Second, the federal government's National Institute on Drug Abuse (NIDA) offers hundreds of millions of dollars in easy money to researchers willing to make claims about marijuana's harms — surely to increase with NIDA's recent establishment of the nation's first "Center on Marijuana Addiction." (Click here for NIDA's own research comparing the addictive properties of popular drugs, finding that even caffeine use causes stronger symptoms of dependence, withdrawal, and tolerance than marijuana.) The third factor in the proliferation of quack marijuana science is the general willingness of the mainstream media to buy government scare tactics hook, line and sinker. This dates back to the prohibition of marijuana in the 1930s, when journalists dutifully parroted Harry Anslinger's claims that one marijuana cigarette will transform children into murderous psychopaths and similarly senseless propaganda.

The silver lining is that people from all walks of life are beginning to question the government's truthfulness when it comes to its drug policies. The emergence of the Internet as both a source for news and watchdog to the mainstream media has been critical to this process. The House of Representatives' Domestic Policy Subcommittee also recently convened a hearing to examine the effectiveness and accountability of the ONDCP. The chairman of that committee issued a statement squarely condemning the Office for its failure to report any concrete successes, its unwillingness to comply with Congress' standards of accountability, and its lack of "consistent or useful performance measures."

Let's hope that growing numbers of policymakers, media commentators and everyday people are willing to put science over politics and support rational alternatives to the disastrous "war on drugs."

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