DURHAM, N.H. — New research from the University of New Hampshire shows that the “gateway effect” of marijuana — that teenagers who use marijuana are more likely to move on to harder illicit drugs as young adults — is overblown.

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Whether teenagers who smoked pot will use other illicit drugs as young adults has more to do with life factors such as employment status and stress, according to the new research. In fact, the strongest predictor of whether someone will use other illicit drugs is their race/ethnicity, not whether they ever used cannabis.

Conducted by UNH associate professors of sociology Karen Van Gundy and Cesar Rebellon, the research appears in the September 2010, issue of the Journal of Health and Social Behavior in the article, “A Life-course Perspective on the ‘Gateway Hypothesis’.”

“There seems to be this idea that we can prevent later drug problems by making sure kids never smoke pot,” Dr. Van Gundy, told CBS News. “But whether marijuana smokers go on to use other illicit drugs depends more on social factors like being exposed to stress and being unemployed – not so much whether they smoked a joint in the eighth grade.”

“In light of these findings, we urge U.S. drug control policymakers to consider stress and life-course approaches in their pursuit of solutions to the ‘drug problem,’ ” Van Gundy and Rebellon say.

The researchers used survey data from 1,286 young adults who attended Miami-Dade public schools in the 1990s. Within the final sample, 26 percent of the respondents are African American, 44 percent are Hispanic, and 30 percent are non-Hispanic white.

The researchers found that young adults who did not graduate from high school or attend college were more likely to have used marijuana as teenagers and other illicit substances in young adulthood. In addition, those who used marijuana as teenagers and were unemployed following high school were more likely to use other illicit drugs.

However, the association between teenage marijuana use and other illicit drug abuse by young adults fades once stresses, such as unemployment, diminish.

“Employment in young adulthood can protect people by ‘closing’ the cannabis gateway, so over-criminalizing youth marijuana use might create more serious problems if it interferes with later employment opportunities,” Van Gundy says.

In addition, once young adults reach age 21, the gateway effect subsides entirely.

“While marijuana use may serve as a gateway to other illicit drug use in adolescence, our results indicate that the effect may be short-lived, subsiding by age 21. Interestingly, age emerges as a protective status above and beyond the other life statuses and conditions considered here. We find that respondents ‘age out’ of marijuana’s gateway effect regardless of early teen stress exposure or education, work, or family statuses,” the researchers say.

The researchers found that the strongest predictor of other illicit drug use appears to be race-ethnicity, not prior use of marijuana. Non-Hispanic whites show the greatest odds of other illicit substance use, followed by Hispanics, and then by African Americans.

The University of New Hampshire, founded in 1866, is a world-class public research university with the feel of a New England liberal arts college. A land, sea, and space-grant university, UNH is the state’s flagship public institution, enrolling more than 12,200 undergraduate and 2,200 graduate students.