On Tuesday, January 29 — three days prior to the publication of a forthcoming study assessing marijuana use and cancer — Reuters News Wire published a story under the headline: “Cannabis Bigger Cancer Risk Than Cigarettes.” Mainstream media outlets across the globe immediately followed suit. “Smoking One Joint is Equivalent to 20 Cigarettes, Study Says,” Fox News declared, while Australia’s ABC broadcast network pronounced, “Experts Warn of Cannabis Cancer ‘Epidemic.‘”
If those headlines weren’t attention-grabbing enough, one only had to scan the stories’ inflammatory copy — much of which was lifted directly from press statements provided by the study’s lead author in advance of its publication.
“While our study covers a relatively small group, it shows clearly that long-term cannabis smoking increases lung-cancer risk,” chief investigator Richard Beasley declared. Beasley went on to speculate that pot “could already be responsible for one in 20 lung cancers diagnosed in New Zealand” before warning: “In the near future we may see an ‘epidemic’ of lung cancers connected with this new carcinogen.”
The mainstream press, always on the look out for a good pot scare story, ran blindly with Beasley’s remarks. Apparently not a scribe among them felt any need to confirm whether Beasley’s study — which remained embargoed at the same time it was making worldwide headlines — actually said what was claimed.
For those who actually bothered to read the study’s full text, which appeared in the European Respiratory Journal days after the global feeding frenzy had ended, they would have learned the following. Among the 79 lung cancer subjects who participated in the trial, 70 of them smoked tobacco. These individuals, not surprisingly, experienced a seven-times greater risk of being diagnosed with lung cancer compared to tobacco-free controls. As for the subjects in the study who reported having used cannabis, they — on average — experienced no statistically significant increased cancer risk compared to non-using controls (Beasely et. al. 2oo8).
So how’d the press get the story so wrong? There are several reasons. First, beat writers based their stories on a press release rather than the study itself. Unfortunately, this is a common practice used by the mainstream media when writing about cannabis-related science. More often than not, media outlets strive to publish their reports prior to a study’s publication — a desire that all but forces reporters to write about data they have never seen. (Likewise, as a marijuana law reform advocate I’m also frequently asked by the press to comment on studies that are not yet public, though I typically choose not to.)
Second, the media chose to selectively highlight data implicating cannabis’s dangers while ignoring data implicating its relative safety. In this case, the study’s authors (and, by default, the worldwide press) chose only to emphasize one small subgroup of marijuana smokers (those who reported smoking at least one joint per day for more than ten years). These subjects did in fact, experience an elevated risk of lung cancer compared to non-using controls. (Although contrary to what the press reported, even the study’s heaviest pot smokers never experienced an elevation comparable to those subjects who reported having “ever used” tobacco.) By contrast, cannabis consumers in the study who reported light or moderate pot use actually experienced a decreased cancer risk compared to non-using controls. (Bottom line, the sample size in all three subgroups is far too small to draw any sound conclusions.)
Finally, the mainstream media failed to employ its own institutional memory. For example, some 18 months earlier The Washington Post and other newspapers around the world reported, “The largest study of its kind has unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer.” That study, conducted by researchers at UCLA, assessed the potential association between marijuana smoking and cancer in over 2,200 subjects (versus only 324 in the New Zealand study), and determined that pot smoking was not positively associated with cancers of the lung or upper aerodigestive tract — even among individuals who reported smoking more than 22,000 joints during their lifetime (Kaufman 2006).
Prior large-scale population studies have reached similar conclusions. For instance, a NIDA (US National Institute on Drug Abuse) sponsored study of 164 oral cancer patients and 526 controls determined, “The balance of the evidence does not favor the idea that marijuana as commonly used in the community is a causal factor for head, neck or lung cancer in adults” and a 1997 Kaiser Permanente retrospective cohort study of 65,171 men and women in California found that cannabis use was not associated with increased risks of developing tobacco-use related cancers — including lung cancer, breast cancer, prostate cancer, colorectal cancer, or melanoma (Sidney et. al. 1997). In fact, even the prestigious National Academy of Sciences, Institute of Medicine says definitively, “There is no conclusive evidence that marijuana causes cancer in humans, including cancers usually related to tobacco use” (Joy et. al. 1999). (Tellingly, when I referred various reporters to these prior studies, I was consistently told that this information was irrelevant because they were assigned to write “only about this study.”)
In short, had the mainstream media even taken the time to consult their own prior marijuana coverage, they would have immediately begun asking the sort of probing questions that the public normally expects them to. Of course, such hard and steadfast rules governing professional journalism seldom apply to the media’ coverage of pot — where political ideology typically trumps accuracy and where slipshod reporting hardly ever even warrants a public retraction. Writing in the Journal of Science nearly 40 years ago, New York state university sociologist Erich Goode aptly observed: “[T]ests and experiments purporting to demonstrate the ravages of marijuana consumption receive enormous attention from the media, and their findings become accepted as fact by the public. But when careful refutations of such research are published, or when latter findings contradict the original pathological findings, they tend to be ignored or dismissed.”
How little has changed.