The buck stops here. Photographer: Matthew Staver/Bloomberg
The buck stops here. Photographer: Matthew Staver/Bloomberg

One of Andrew Sullivan's readers has an interesting theory about why marijuana might be a gateway drug:

Since we're on to the topic of "marijuana as a gateway drug", I'd like to bring up an argument I almost never hear, and have no idea why: Isn't it possible that marijuana acts as a gateway drug for some people because they buy those other drugs from the same guy? I'm sure a lot of people have gotten the Amazon-sales pitch from their pot dealer ("If you like marijuana, you might also enjoy ... "). I have never been tempted, but if I wanted to try cocaine or mushrooms, etc., I would probably just ask the guy I buy pot from. My guess is that legalizing marijuana and putting it in pharmacies would limit people's access to harder drugs for this very reason.

I'm not sure how true this is -- most people I know who tried harder drugs got them from the friends they smoked pot with, not the guy who sold it to them. On the other hand, it's at least plausible ... which would mean that although legalization would probably cause marijuana use (and abuse) to rise, the paradoxical result might be a decline in the use of harder drugs.

The only way to find out is to legalize and see what happens. Fortunately for the curious, two states are experimenting right now. We should have our answer in a few years.

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Megan McArdle writes about economics, business and public policy for Bloomberg View. Follow her on Twitter at @asymmetricinfo.

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