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More stupid science tricks

Will we see another spate of alarmist headlines from this?

Marijuana tied to precancerous lung changes
Smoking marijuana can cause changes in lung tissue that may promote cancer growth, according to a review of decades of research on marijuana smoking and lung cancer.
Still, it is not possible to directly link pot use to lung cancer based on existing evidence.

No evidence of cancer. Never has been. Despite numerous studies and millions of users.
Now check out this stunning train of reasoning.

“We must conclude that no convincing evidence exists for an association between marijuana smoking and lung cancer based on existing data,” Mehra and her team write.
Nevertheless, they add, the precancerous changes seen in studies included in their analysis — as well as the fact that marijuana smokers generally inhale more deeply and hold smoke in their lungs longer than cigarette smokers, and that marijuana is smoked without a filter — do suggest that smoking pot could indeed boost lung cancer risk. It is known, they add, that marijuana smoking deposits more tar in the lungs than cigarette smoking does.
The failure to find a marijuana-lung cancer link may have been due to methodological flaws in existing research, rather than the absence of such a link, the researchers say. Doctors should advise their patients that marijuana does indeed have potential adverse effects, they conclude, including causing precancerous changes in the lungs. [emphasis added]

So, despite the fact that there is no evidence for marijuana causing cancer, the researchers have this gut feeling that it might anyway (plus all the other research might be flawed). Thus, based on the chance that their gut feeling is right and all the other scientific evidence is wrong, they want doctors to warn their patients about something they are supposed to call precancerous changes in the lungs, despite the continued and overwhelming lack of any evidence of a cancer link!
Now there are actual things that doctors could warn their patients about — such as the danger of bronchial conditions from marijuana smoke, without confusing them with this ignorant claptrap.
Update: Here’s the review article.
Further update: From daksya in comments:

The study takes into account only 4 studies which checked on “Marijuana (MJ) Use Exposure and Other Lung Cancer Outcomes” i.e. actual outcome of lung cancer, as opposed to precancerous changes. Of these 4 studies, two didn’t take tobacco use into account, and the low study quality score reflects that. Of the other 2 studies, the familiar Sidney study of nearly 65,000 participants did not find an increased risk of any cancers, and finally a case-control study of 353 male patients in Morocco (Sasco et al.) found a odds ratio of 1.99 (incorrectly reported as 1.93 in this paper) among consumers of hashish/kiff. Now there were 15 hashish/kiff users among cancer cases and 12 among controls, hardly enough to inspire confidence. More importantly, this review claims that tobacco use was controlled for in this study. Incorrect, “smoking status” was accounted for. Now, it turns out that kiff itself is a mixture of 2/3rd dried cannabis powder and 1/3rd tobacco. In other words, all smoke but no fire.

Note: The review was funded in part by NIDA.
Also: Can you believe the title of the review?

The Association Between Marijuana Smoking and Lung Cancer
A Systematic Review

Reena Mehra, MD, MS; Brent A. Moore, PhD; Kristina Crothers, MD; Jeanette Tetrault, MD; and David A. Fiellin, MD should be ashamed.

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