Why Smoking Marijuana Doesn't Make You a Junkie

Two recent studies should be the final nails in the coffin of the lie that has propelled some of this nation's most misguided policies: the claim that smoking marijuana somehow causes people to use hard drugs, often called the "gateway theory."

Such claims have been a staple of the White House Office of National Drug Control Policy under present drug czar John Walters. Typical is a 2004 New Mexico speech in which, according to the Albuquerque Journal, "Walters emphasized that marijuana is a 'gateway drug' that can lead to other chemical dependencies."

The gateway theory presents drug use as a tidy progression in which users move from legal drugs like alcohol and tobacco to marijuana, and from there to hard drugs like cocaine, heroin and methamphetamine. Thus, zealots like Walters warn, marijuana is bad because it leads to things that are even worse.

It's a neat theory, easy to sell. The problem is, scientists keep poking holes in it -- the two new studies being are just the most recent examples.

In one National Institute on Drug Abuse-funded study, researchers from the University of Pittsburgh tracked the drug use patterns of 224 boys, starting at age 10 to 12 and ending at age 22. Right from the beginning these kids confounded expectations. Some followed the traditional gateway paradigm, starting with tobacco or alcohol and moving on to marijuana, but some reversed the pattern, starting with marijuana first. And some never progressed from one substance to another at all.

When they looked at the detailed data on these kids, the researchers found that the gateway theory simply didn't hold; environmental factors such as neighborhood characteristics played a much larger role than which drug the boys happened to use first. "Abusable drugs," they wrote, "occupy neither a specific place in a hierarchy nor a discrete position in a temporal sequence."

Lead researcher Dr. Ralph E. Tarter told the Pittsburgh Post-Gazette, "It runs counter to about six decades of current drug policy in the country, where we believe that if we can't stop kids from using marijuana, then they're going to go on and become addicts to hard drugs."

Researchers in Brisbane, Australia, and St. Louis reached much the same conclusion in a larger and more complex study published last month. The research involved more than 4,000 Australian twins whose use of marijuana and other drugs was followed in detail from adolescence into adulthood.

Then -- and here's the fascinating part -- they matched the real-world data from the twins to mathematical models based on 13 different explanations of how use of marijuana and other illicit drugs might be related. These models ranged from pure chance -- assuming that any overlap between use of marijuana and other drugs is random -- to models in which underlying genetic or environmental factors lead to both marijuana and other drug use or models in which marijuana use causes use of other drugs or vice versa.

When they crunched the numbers, only one conclusion made sense: "Cannabis and other illicit drug use and misuse co-occur in the population due to common risk factors (correlated vulnerabilities) or a liability that is in part shared." Translated to plain English: the data don't show that marijuana causes use of other drugs, but instead indicate that the same factors that make people likely to try marijuana also make them likely to try other substances.

In the final blow to claims that marijuana must remain illegal to keep us from becoming a nation of hard-drug addicts, the researchers added that any gateway effect that does exist is "more likely to be social than pharmacological," occurring because marijuana "introduces users to a provider (peer or black marketeer) who eventually becomes the source for other illicit drugs." In other words, the gateway isn't marijuana; it's laws that put marijuana into the same criminal underground with speed and heroin.