Marijuana is thought by some to be a gateway drug among young people who eventually go on to try stronger substances. But that may be the exception rather than the rule, a new study finds.

Researchers from the University of New Hampshire looked at data from a random group of 1,286 children, teens and young adults who were in Miami-Dade public schools in the 1990s. Among the study participants, 26% were African American, 44% were Hispanic, and 30% were non-Hispanic white.

They were asked about their substance use and about exposure to major events and traumas that occurred before age 13. Some questions included, “Did you ever fail a grade at school?”, “Did your parents ever divorce/separate?” and “Were you regularly emotionally abused by one of your caretakers?”

Education played a role in use of other substances--those more likely to have used marijuana as teens and other drugs as young adults didn’t graduate from high school or go to college. Employment factored in as well, since those who smoked pot as teens and were out of work after high school were more apt to use other drugs.

Researchers also discovered that if young adults became involved with other substances after using marijuana as teens, that link didn’t hold once the sources of stress, such as not working, went away.

Age was yet another issue. Researchers discovered that after the age of 21, the gateway effect seemed to disappear.

The results could have implications for drug policy, the study authors argue. “Employment in young adulthood can protect people by ‘closing’ the marijuana gateway,” said lead author Karen Van Gundy, in a news release, “so over-criminalizing youth marijuana use might create more serious problems if it interferes with later employment opportunities.”

The study appears in the September issue of the Journal of Health and Social Behavior.

-- Jeannine Stein / Los Angeles Times