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April 21, 2014 9:03 AM Cannabis Use and Problem Drinking: NORML Tries a Fast One

By Mark Kleiman

Sometimes b.s. science in support of drug policy advocacy reflects the choices of the scientists. Sometimes it reflects the choices of the advocates.

I got a note from a friend about a report that frequent cannabis users consume less alcohol. Of course, it would be fabulous news if cannabis use actually substituted for heavy drinking; to my mind, that would make the case for cannabis legalization a near lay-down, and the case for high taxes and tight restrictions rather dubious.

The note was based on a NORML press release with a very encouraging headine:

Study:
Frequent Cannabis Consumers Less Likely To Engage In Problematic Alcohol Use

And the lead paragraph was consistent with the headline: “Those who report consuming cannabis two or three times per week are less likely to engage in at risk drinking behavior, according to data published online in The American Journal of Addictions.”

So I rushed to read the actual paper. Yes indeed: frequent cannabis users were less likely to engage in problem drinking compared to occasional cannabis users. Ooops!

Here’s the summary by the sciencists, right at the top of their paper:

Cannabis users were more likely to report hazardous alcohol use, use of other illicit drugs, and unauthorized use of prescription drugs than were non-users. Within the group of active cannabis users, frequent cannabis use, compared to occasional use, was associated with the use of other illicit drugs and negatively associated with hazardous alcohol use.

[emphasis added]

In fact, if you compare heavy cannabis users (here defined as 2-3x/week or more with non-users, they’re slightly more likely to engage in problem drinking. It’s just that they’re better off in that regard than occasional users.

So the accurate summary of the paper would be: cannabis smoking in Sweden is associated with problem drinking, but less so among frequent smokers than among occasional smokers.

See how it’s done? Simply by omitting the crucial qualfier, you can convert a finding that’s unhelpful to your cause to a finding that’s extremely helpful. Now kids, these are trained PR professionals; don’t try this at home.

Pot-smoking in Sweden is fairly rare; only 2.7% of the weighted sample reported any use. (The comparable figure in the U.S. would be more like 15%.) Of those, more than 90% were categorized as occasional users: remember, that’s the group with more alcohol abuse. Only 9.7% (weighted) were in the frequent-user group. So the possible protective effect applies to something less than half a percent of the population. At that rate, cannabis isn’t likley to contribute much to alcohol-abuse prevention, even if there’s a real effect, which of course we don’t know. The study is purely correlational, leaving the causal relationships utterly undefined. A response rate of under 30% further complicates interpretation. Nor do we know what happens over time; what’s the effect of heavy cannabis use at time T on problem drinking at T + 1, T + 2, …?

Even so, the negative correlation between cannabis frequency and heavy drinking isn’t what I would have expected; this is a finding the calls for follow-up research.

But the main thing I learned is not to trust NORML press releases.

Several people have noticed that my usually sunny disposition turns a bit more stormy when I participate in drug-policy debates. Is it any wonder? I think I deserve some credit for not having actually strangled anyone.

Update The author of the press release replies:

Yes, you are correct. This is what the paper said. I believed this point was made clear in the press release here:

“Researchers reported that frequent cannabis consumers (defined as having used cannabis two or three times per week) were less likely to engage in hazardous drinking practices compared to infrequent users (those who reported having consumed cannabis fewer than four times per month).”

They concluded: “Among cannabis users, frequent cannabis use is associated with a higher prevalence of other illicit drug use and a lower prevalence of hazardous alcohol use when compared to occasional cannabis use.”

The conclusion that the heavier cannabis users reported less incidences of hazardous drinking compared to ‘infrequent users’/’occasional users’ is made clear in the third and fourth paragraph using those exact terms. Your summary implies I never made this point clear at all and that is simply untrue.

In hindsight I agree that I arguably should have also made this point more clear in the lede, but I did make it explicitly clear the third paragraph and also quoted the paper’s authors in the fourth graph. The summary of the paper itself was only four paragraphs. (The fifth graph refers to a separate paper.) I would hardly call this a ‘fast one.’

It seems to me that failing to mention that both cannabis users over all, and even the heavy users, were more involved with at-risk drinking than non-users was a serious problem. But your mileage may vary.

[Cross-posted at The Reality-Based Community]

Mark Kleiman is a professor of public policy at the University of California Los Angeles.

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