Democracy in America | Legalising pot

Is marijuana a gateway drug?

Chris Christie's fears are misplaced

By T.W.

“AS LONG as I am governor of New Jersey, there won’t be legalised marijuana in this state,” vowed Chris Christie, governor of New Jersey, on March 25th. A potential Republican contender in the 2016 presidential race, Mr Christie explained that “every bit of objective data tells us that it’s a gateway drug to other drugs”. Is he right?

The gateway theory seems reasonable enough at first. Most people who take hard drugs start with soft ones. The National Institute on Drug Abuse (NIDA) reports that among people who have tried illicit drugs, about two-thirds began with marijuana. Hardly anyone jumps straight in at the deep end: less than 1% of drug users reported that their first-ever outing was with heroin or cocaine.

But then, it’s also a fact that most heroin addicts had previously tried chocolate. The trouble is that marijuana is so common—about four out of ten Americans, including the president, admit to having tried it—that any abuser of hard drugs is likely to have encountered it along the way. Establishing a causal link is the tricky bit.

Proponents of the “gateway” theory cite two arguments. One is biological: lab rats exposed to THC, the fun bit in marijuana, show greater sensitivity when later exposed to other drugs, such as morphine. Alcohol and nicotine have the same “cross-sensitising” effect. In other words, rats (and perhaps people) that have tried one gently mind-altering substance seem to get more of a kick out of others.

The other argument is social: smoking marijuana, a banned substance, gets youngsters in with the wrong crowd, making them more likely to flout other laws. Breaking one taboo makes it easier to break another. And knowing a marijuana dealer certainly makes it simpler to acquire other substances: drug pushers are notorious for giving free samples of new drugs to their customers.

The first argument is in Mr Christie’s favour. Exposing more people to marijuana, as legalisation probably would, could prime more brains to enjoy other substances. The effect would probably be weak, since those same brains are already exposed to alcohol and tobacco, which have the same sensitising effect. Nonetheless, legalisation would give people another way to mess with their minds. Not everyone would prosper.

But the second argument rather undermines Mr Christie’s position. To the extent that marijuana acts as a social gateway to other drugs, legalisation slams that gateway shut. In Colorado and Washington—and, soon, Alaska and Oregon—marijuana is sold not by drug pushers but by heavily regulated dispensaries, which sell only one drug. The chances of being offered hard drugs under the counter in a Denver pot shop are roughly the same as being offered cocaine along with your beer by a cashier in Walmart.

It will be years before the full effects of legalisation are known—after all, an academic debate continues about the impact of the prohibition on alcohol in the 1920s and 30s. But the bigger picture suggests that there is little reason to panic. In the past few years, the number of monthly marijuana users in America has steadily risen, from 14.4m in 2007 to 18.9m in 2012. If marijuana were a gateway to harder drugs, one might expect those drugs to become more popular too. Yet during the same period, consumption of most other substances actually fell. The number of monthly cocaine users dipped from 2.1m to 1.7m and the number of people using methamphetamine (“crystal meth”) fell from 530,000 to 440,000. Heroin use has been going up, but the gateway drug there seems to be prescription painkillers. Mr Christie’s worries are misplaced.

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