Another anti-marijuana "fact" debunked

Study finds marijuana not a cause for lung cancer; Results 'against our expectations,' researchers say. (Chronicle login: semods4@yahoo.com; pw = speakeasy)

>> The largest study of its kind has unexpectedly concluded that smoking marijuana, even regularly and heavily, does not lead to lung cancer.

The new findings "were against our expectations," said Donald Tashkin of the University of California at Los Angeles, a pulmonologist who has studied marijuana for 30 years. "We hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use," he said. "What we found instead was no association at all, and even a suggestion of some protective effect."

Federal health and drug enforcement officials have widely used Tashkin's previous work on marijuana to make the case that the drug is dangerous. Tashkin said that while he still believes marijuana is potentially harmful, its cancer-causing effects appear to be of less concern than previously thought. <<

It's long past time marijuana was put on the same basis as cigarettes and alcohol -- legally restricted to adults, but readily available (and taxable!) in stores. The amount of tax money (and law enforcement person-hours wasted) seeking out pot dealers and users, and the number of lives destroyed by the government's vendetta against weed, surpasses tragic ant enters the realm of the obscene. And, btw, I haven't had a "joint" in well over 20 years now, so this is not a matter of special personal interest.

-- Dave K, Speakeasy Moderator
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http://www.scienceblog.com/cms/study-finds-no-link-between-marijuana-use-and-lung-cancer-10660.html

They limited the study to people under age 60. ''If you were born prior to 1940, you were unlikely to be exposed to marijuana use during your teens and 20s--the time of peak marijuana use,'' Dr. Tashkin said. People who were exposed to marijuana use in their youth are just now getting to the age when cancer typically starts to develop, he added.

About half the cancer cases studied were lung cancer. The average age of people diagnosed with lung cancer is 70 years old.

Also,

The study found that 80% of lung cancer patients and 70% of patients with head and neck cancer had smoked tobacco, while only about half of patients with both types of cancer smoked marijuana.

So for the lung cancer group of ~600, about 480 had some history of cigarette use. Only 300 were marijuana suers leaving 300 that were not. So even if one assumes that all of the 120 non-smokers were among the tokers, that still leaves 180 tokers that HAD to be tobacco smokers too. How do you control for smoking tobacco in this sample? You would have to match non-smoking tokers in your case-control study. They further break down the tokers into degrees of exposure -- FIVE categories (see below). Remember, AT MOST you can have only 120 non-smoking tokers in this group, probably fewer. Please correct me if that logic seems off. I keep hoping I'm missing something here!

This is the best summary of the study I could find

From DK's article
The heaviest marijuana smokers had lit up more than 22,000 times, while moderately heavy usage was defined as smoking 11,000 to 22,000 marijuana cigarettes.

From the above link:
Among them, 46% had never used marijuana, 31% had used for less than one joint year, 12% had used for 1-10 j-yrs, 5% had used 10-30 j-yrs, 2% had used for 30-60 j-yrs, and 3% had used for more than 60 j-yrs.

the 22,000 = 60 j-yrs and the 11-22K group is the 30-60 j-yrs group. These are THREE and TWO percent of the group respectively. Of the ~600 we are talking sample size of 30 moderately heavy & heavy users. Also, since the tokers add up to 54% of the group, and 5% are in the two heaviest use categories, approximately 10% of the tokers are heavy use.

{note 1 j-yr = (1 joints per day x years that number smoked ... This is such a broad category that it probably includes a significant number of people that for all intent and purposes would be considered non-smokers -- e.g. tried it a few times in college, that's <1 but >0 ... but I digress).

Going back to the numbers from before, we can have at MOST 120 TOTAL non-smoking tokers that contracted lung cancer. Assuming that their MJ use is divided as for the whole sample (10% of tokers in highest use categories), only TWELVE of these are in the heaviest toking samples -- split into two groups at that (no round numbers, about 5 moderately heavy and 7 very heavy) . These are further matched with controls for age, gender and neighborhood?? I would love to see the statistics of this analysis.

From my last link, this study and its findings are almost one year old. No journal article citation yet (they usually at least pop up in Google as abstracts even if the articles aren't available online). I'm on summer break so no access to the search for this. DK if you can find journal citations, I would appreciate it.

Wonder what political push for MJ is on the horizon for this to be reported now?!

I'm NOT an empidemiologist, nor do I play one in SE, but I do have a fair amount of education and experience in a related field (as well as an excellent stats background). I can't for the life of me understand why this sort of study is done in the first place instead of randomly sampling two groups -- non-smoking tokers vs. non-smoking non-tokers -- and comparing cancer rates among them. THAT seems far more straightforward. Maybe DK knows someone that can offer the explanation? At present I'm shaking head left to wonder if it's just easier to baffle with statistics with studies of this nature.

Another anti-marijuana "fact" debunked

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