Latest Anti-Pot Quack Science: 'Marijuana Makes Your
Teeth Fall Out'
By Bruce Mirken, AlterNet
Posted on February 9, 2008, Printed on February 9,
Recent weeks have seen a rash of new studies of
marijuana hitting the mass media, generating scary
headlines like "Smoking Pot Rots Your Gums," "Cannabis
Bigger Cancer Risk Than Cigarettes," and "Pot
Withdrawal Similar to Quitting Cigarettes. Most of
this coverage can be boiled down to a fairly simple
Flawed science + uncritical reporting =
Mercifully, the U.S. mass media were so distracted by
Super Tuesday, Heath Ledger's autopsy and the latest
Britney Spears trauma that reports of these studies
didn't get as much play as they might have. That's
good, because the research had significant gaps, and
the reporting ranged from slapdash to flat wretched.
LUNG CANCER: A JOINT = 20 CIGARETTES?
The lung cancer study was the scariest. Since
cigarettes are a known lung cancer risk, it seems
plausible that marijuana might carry similar risks. In
fact, most of the scientific evidence tends in the
opposite direction -- though one would never know it
from reading either the study or the Reuters wire
story that got the heaviest circulation.
Conducted in New Zealand, this was what is called a
"case-control" study, in which researchers looked at a
group of patients who had lung cancer and compared
them to a group without cancer -- the controls --
matched for age and other demographics. All were asked
about various factors that might increase their lung
cancer risk, including smoking cigarettes or
marijuana. After running the data on 79 cancer cases
and 324 controls through myriad equations and
mathematical analyses, the researchers proclaimed that
one joint packed a cancer risk roughly equal to 20
cigarettes -- an assertion that became Reuters' lead.
What was downplayed in the study, published in the
European Respiratory Journal, and missing entirely
from most media reports was context -- context that
strongly suggests that its alarming conclusion is
For one thing, the new conflicts with other, much
larger studies. In a study published in 1997,
Kaiser-Permanente researchers followed 65,000 patients
for 10 years and saw no sign of marijuana use
increasing the risk of lung cancer or other
smoking-related cancers. And a UCLA study similar in
design to this one, published in 2006, found a trend
toward lower lung cancer rates among marijuana
smokers. Instead of 79 cancer cases, the UCLA team
looked at 1,212. The result was so striking that they
speculated that it "may reflect a protective effect of
That's right: Marijuana might protect from cancer.
Piles of published studies going back to the mid-1970s
document the cancer-fighting properties of marijuana's
active components, THC and other chemicals called
cannabinoids. Anticancer activity has been shown in
many types of malignant cells, including lung cancer
cells. So even though marijuana smoke contains tars
and other potentially carcinogenic compounds, it is
entirely plausible that cannabinoids counter any
But even without such context, a closer look at the
New Zealand data raises questions that should have
been asked by reporters. For example, most marijuana
smokers in the study actually didn't show an increased
risk of cancer. The only group that did was those
whose marijuana use equaled at least 10.5
"joint-years" (one joint-year equals smoking a joint
every day for one year). That group constituted a
whopping 14 people. All those complicated mathematical
models leading to the "20 times the risk" assertion,
and contradicting reams of published research, rest on
exactly 14 people.
DOES MARIJUANA ROT YOUR GUMS?
The gum disease study was even more tenuous, but again
you would never know it from most of the coverage.
Researchers -- also in New Zealand -- followed 903
participants from birth through age 32. At ages 18,
21, 26, and 32, they were asked whether they had used
marijuana in the past year, and how often. The
heaviest marijuana users had a 60 percent increased
risk for gum disease after controlling for several
factors that might affect their risk, including
cigarette use and professional dental care.
The researchers were careful to say they hadn't proved
cause-and-effect, but simply what scientists called an
"association." But that didn't stop one U.S. reporter
from writing that marijuana "could ... destroy gum
tissue," and an Australian headline writer from
declaring that marijuana "makes teeth fall out."
Reading the actual study -- something one suspects
most reporters never did -- raises questions the media
never asked. Why is there no indication that
participants were questioned about use of alcohol or
other illicit drugs, both of which are known risk
factors for dental and gum problems? Why were they not
asked about brushing and flossing habits?
Given the relatively small effect -- the statistical
margin of error meant that the increased risk could be
as low as 16 percent -- confounding by alcohol/drug
use or poor dental hygiene could easily explain the
whole difference. In other words, there is a very good
chance this study found nothing real at all.
I raised this issue with an editor at one news
organization, whose story had been particularly
hysterical and lacking in context, asking why they
hadn't noted these potential doubts. The rather snippy
reply: "As for the rest of your concerns, we are
dealing with a peer-reviewed journal study, and I
don't feel at all comfortable going beyond what they
are publishing. That is not our role."
Memo to editors: Journal peer-reviewers are human.
They sometimes miss stuff. When did it stop being a
reporter's job to ask questions?
MARIJUANA AS ADDICTIVE AS TOBACCO?
If you haven't lost your teeth or died of lung cancer
yet, another set of grim headlines warned that
marijuana is as addictive as tobacco -- again, a
conclusion that went beyond the study's findings and
which was almost certainly wrong.
In this U.S. study, researchers took 12 people who
regularly smoked both marijuana and cigarettes and had
them stop using one, the other, and both, in varying
orders. Physiological tests and responses to
questionnaires were used to assess withdrawal symptoms
such as irritability and difficulty sleeping. The
withdrawal symptoms reported were roughly comparable.
But the limitations of this research are obvious. In
fairness, most were acknowledged in the study,
published in the journal Drug and Alcohol Dependence.
For one, the study looked only at regular users of
both substances, so it tells nothing about marijuana
users who do not use tobacco -- a considerable number,
by most accounts. Second, the researchers did not
publish the results for individual participants. In a
sample of 12, one or two extreme responses can skew
the averages enough to make them meaningless.
The researchers also did not note any changes in
participants' use of caffeine or alcohol, which could
easily have affected their findings. Volunteers were
asked not to change their use of these substances, but
we have no clue whether they followed these
And though the overall withdrawal symptom ratings were
similar, ratings of anger and craving were higher for
tobacco than for marijuana. And even in areas where
the two substances were statistically comparable,
there was often a trend toward the tobacco withdrawals
being stronger. Had this been a larger study, those
trends might have reached statistical significance.
Also, the 5-day abstinence period may not have been
enough to fully gauge withdrawal effects. For longtime
cigarette smokers, tobacco cravings can continue for
Finally, a reality check: It is an established fact
that about 32 percent of those who ever touch a
cigarette become dependent on tobacco. For marijuana,
the figure is nine percent. In the real world, it's
clear that marijuana is nowhere near as addictive as
tobacco -- but again, you'd never know it from the
coverage of this study.
In fact, you wouldn't learn much from the coverage of
any of these studies.
Bruce Mirken is communications director for the
Marijuana Policy Project.
© 2008 Independent Media Institute. All rights
View this story online at: http://www.alternet.org/story/76496/