14/02/2008 00:00:00
Weed Risk Arguments
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A rash of new studies of marijuana has hit the mass media, generating
absurd headlines like "Smoking Pot Rots Your Gums."
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 equation:
Flawed science + uncritical reporting = misinformation.
Let’s debunk the myths and bad reporting.
Lung cancer: One 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 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 wrong.
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 marijuana."
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 harmful effects.
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.
This issue was raised with an editor at one news organization, whose
story had been particularly hysterical and lacking in context, and the
editor was asked why the paper 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 instructions.
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 five-day abstinence period may not have been enough to fully
gauge withdrawal effects. For long-time cigarette smokers, tobacco
cravings can continue for years.
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.
From ShoutWire.com
http://www.xtaster.co.uk/public/content_article.aspx?id=2526
Source:
http://www.ukcia.org/news/shownewsarticle.php?articleid=13288
Author:
xtaster via UKCIA
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