March 15, 2008
Headlines suggested a study proved pot is a greater cancer risk than
tobacco -- but the media didn't even wait for the report to be released.
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 Tobacco." 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
"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.
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 elevated 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, performed 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.
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. 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." (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 Science
nearly 40 years ago, New York state university sociologist Erich Goode
aptly observed: "Tests 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.