Maddy and Andrew have discussed the recent comparative study of marijuana- and cigarette-smokers that was published in the journal Radiology.
Andrew, quoting the authors’ summary, notes that “airway inflammation and emphysema were more common in marijuana smokers than in nonsmokers and tobacco-only smokers, although variable interobserver agreement and concomitant cigarette smoking among the marijuana-smoking cohort limits our ability to draw strong conclusions.”
Let’s read as well the study’s penultimate paragraph. In full:
Our study had limitations. First, the small sample size precluded us from drawing strong conclusions. Second, the retrospective nature of the study had its own inherent limitations. Third, there was inconsistent quantification of patient marijuana use, due in part to the previous illegal nature of marijuana possession, which led to a lack of patient reporting. Accurate quantification is further complicated by the fact that users often share joints, use different inhalation techniques, and use marijuana of varying potency. Fourth, given that most marijuana smokers also smoke tobacco, the synergistic effects of these two substances cannot be effectively evaluated. Fifth, only a portion of patients could be age matched, since the tobacco-only cohort was taken from the lung cancer screening study and the patients were aged at least 50 years. Due to the age mismatch in the larger cohort, there are differences in the duration of smoking. Lastly, variable interobserver agreement limits our ability to draw strong conclusions about bronchial wall thickening and bronchiectasis.
The sentence I have italicized is important. As the study notes elsewhere, of the 56 marijuana smokers whose chests were scanned, fully 50 also smoked tobacco. Only six participants, then, provided evidence applicable to the question Maddy posed, viz. whether (smoking) marijuana per se is less (or more) harmful than smoking cigarettes per se. Given this tiny sample size of six, the authors drew no conclusions, not even weak ones, about the relative harms of cigarettes-only vs. marijuana-only. Their limited conclusions suggest, rather, that smoking marijuana causes unique identifiable harms, and that the group of marijuana-and-in-all-but-six-cases-cigarette-smokers had a higher frequency of certain harms than did the cigarette-only-smokers and the nonsmokers.
Remember as well that there are ways of consuming the active chemicals in both tobacco and marijuana that do not involve combustion and on which the study sheds no light.
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If the evidence were vast and unambiguous, we would still have to weigh its practical import according to some standard of judgment or action; it does not come with an instruction manual.
Setting aside the untenable view that cannabis presents no health risks — and also individuals’ unequal risk tolerance and perception of benefits — we could distinguish at least two broad normative approaches to managing the risks.
The first, which in principle would be my own, is to weigh the health and public-health evidence about each kind of drug and try to apply consistent standards rooted in the severities of the harms. If you take this approach — and if, like me, you are not persuaded that cannabis is more harmful than tobacco or alcohol — it’s hard not to perceive hypocrisy in the contrast between our current fixation on weed and our comparative indifference to the life- and family-shattering effects of the two psychoactive drugs that have long been available for recreational purchase everywhere. You probably sometimes suspect, as I do, that the juxtaposition of attitudes has less to do with evidence than with stereotypes: Weed is some damn hippie thing, but wine is what you drank with WFB, and tobacco-smokers are victims of the nanny state, the poor dears.
Taking the second approach should restrain that perception of hypocrisy. It is this: Two legal substances that cause harm is worse than one, three is worse than two, etc. From this perspective, the comparison of cannabis with alcohol or tobacco is not especially relevant; what we should want to do is to prevent or mitigate any harms (provided the mitigatory or preventative measures do not themselves cause even greater damage). It’s correct, then, to worry most about the legalizing or popularizing of a new drug, since this is a worsening of the status quo. And the worry grows when one reflects that we do not have much research on the mass use of cannabis at record potency levels.
The problem with the second approach, however, is that it will tend to give us laws whose design is due more to accidents of timing than to a conclusive and objective judgment of risk. Laws that are likely to be, in a word, arbitrary, and therefore, in a second word, unjust. People notice sooner or later, and then they go overboard correcting it.
So in practice, perhaps it will be good for us to take neither approach in its purity as — what seems most likely — we stumble our way along a zigzagging, locally varying, but perhaps, on a national average, gradualist course toward the rationalizing of our laws and attitudes about drugs.