New research finds little support for the hypothesis that marijuana is a "gateway" drug leading to the use of harder drugs in adulthood.
Teens in the study who smoked marijuana were more likely to go on to use harder illicit drugs, but the gateway effect was lessened by the age of 21, investigators say.
Harder drugs in the study referred to illicit drugs that include analgesics, cocaine, hallucinogens, heroin, inhalants, sedatives, stimulants, and tranquilizers.
The study is published in the September issue of the Journal of Health and Social Behavior.
Failure to graduate from high school or find a job were all bigger predictors of drug use in young adulthood than marijuana use during adolescence, says study researcher Karen Van Gundy, who is a sociologist at the University of New Hampshire.
Van Gundy says she did not set out to disprove the idea that marijuana is a gateway drug when she and co-researcher Cesar J. Rebellon examined survey data from 1,300 mostly male Hispanic, white, and African-American young adults who attended south Florida public schools in the 1990s. The participants were followed from enrollment in the sixth or seventh grade until they reached their late teens or early 20s.
"Most of the previous research has examined early drug use among people with serious drug problems," she says. "These people do tend to progress from alcohol and marijuana use to other drugs."
When the teens in the study were followed forward into young adulthood, however, a different picture emerged.
"We were somewhat surprised to find the gateway effect wasn't that strong during the transition to adulthood," Van Gundy says. "It really didn't matter if someone used marijuana or not as a teen."
Specifically, the study found illicit drug abuse in young adulthood to be much more closely linked to stress during the teen years and whether or not the young adults were employed.
But Columbia University sociologist Denise B. Kandel, PhD, whose research early in the decade found marijuana to be a gateway drug, calls the new research highly flawed and the conclusions "ill founded."