By the 1950s, Federal Bureau of Narcotics Commissioner Harry Anslinger had backed away from his claim that marijuana turns people into murderers. Instead he began arguing that it turns them into heroin addicts. "Over 50 percent of those young addicts started on marijuana smoking," Anslinger told a congressional committee in 1951. "They started there and graduated to heroin; they took the needle when the thrill of marijuana was gone."
Half a century later, this idea, known as the "gateway" theory, remains a bulwark of marijuana prohibition. Although the claim that smoking pot makes people more likely to use other drugs is politically useful, a new study from the RAND Corporation's Drug Policy Research Center shows that it is scientifically superfluous.
Survey data indicate that heroin and cocaine users generally use marijuana first, and that people who try pot are much more likely than people who don't to try other drugs. Using a mathematical model incorporating data from the National Household Survey on Drug Abuse, the RAND researchers found that a general predisposition to use drugs, combined with a four-year lag between access to marijuana and access to other illegal intoxicants, was enough to account for these patterns.
"The people who are predisposed to use drugs and have the opportunity to use drugs are more likely than others to use both marijuana and other drugs," said Andrew Morral, the lead author of the study, which appeared in the December issue of the journal Addiction. "Marijuana typically comes first because it is more available. Once we incorporated these facts into our mathematical model of adolescent drug use, we could explain all of the drug use associations that have been cited as evidence of marijuana's gateway effect."
A spokesman for the Drug Enforcement Administration, successor to Anslinger's bureau, was unimpressed by the distinction between correlation and causation. "Whether you want to use the gateway argument for the reason why marijuana is illegal or any other argument," he told WebMD Medical News, "the fact is, the majority of cocaine and heroin users first used marijuana before moving on to those other drugs."