Marijuana is not a "gateway" drug that predicts or leads to drug abuse, a 12-year University of Pittsburgh study has found. The study is only the latest -- see here and here -- to undermine the argument that trying marijuana makes young people more susceptible to using other drugs.

That argument, that marijuana is a "gateway" drug, remains a favorite argument of prohibitionists despite its continual refutation. The "gateway theory" is also a perennial favorite of the press, as journalist Ryan Grim noted in his "Gateway to Nowhere?" earlier this year at Slate.com.

The Pittsburgh researchers tracked 214 boys beginning at ages 10-12, all of who eventually used either legal or illegal drugs. They were tracked to age 22, then categorized into three groups: those who used only alcohol or tobacco, those who started with alcohol and tobacco and then used marijuana (gateway sequence) and those who used marijuana prior to alcohol or tobacco (reverse sequence).

The researchers found that 22% of the boys who used both legal and illegal drugs at some point started with marijuana, then moved on to tobacco and alcohol -- the reverse of the gateway sequence. Those youths who began with marijuana were no more likely to develop a substance use disorder than those who followed the traditional succession of alcohol and tobacco before illegal drugs, according to the study.

"The gateway progression may be the most common pattern, but it's certainly not the only order of drug use," said Ralph Tarter, PhD, professor of pharmaceutical sciences at the University of Pittsburgh School of Pharmacy and lead author of the study. "In fact, the reverse pattern is just as accurate for predicting who might be at risk for developing a drug dependence disorder."

The best predictors of future drug use were not the order in which someone began using a set of drugs, but having grown up in a tougher neighborhood, having more exposure to drugs in the neighborhood, and having lesser parental involvement. But most important, the study said, was "a general inclination for deviance from sanctioned behaviors."

Trying to portray marijuana as a "gateway" to harder drug use is an error with serious consequences, said Dr. Tarter. "The emphasis on the drugs themselves, rather than other, more important factors that shape a person's behavior, has been detrimental to drug policy and prevention programs. To become more effective in our efforts to fight drug abuse, we should devote more attention to interventions that address these issues, particularly to parenting skills that shape the child's behavior as well as peer and neighborhood environments."