THURSDAY, Nov. 19 (HealthDay News) -- Parents who take the time to know what their teenage children are up to and have strong anti-drug views can be effective in reducing their children's marijuana use, a new study says.

Among all the illicit drugs, marijuana is the most widely used by teens, with nearly 42 percent of high school seniors having tried it, according to the study authors.

"We've been working on attenuating drug use in kids," said lead researcher William Crano, a professor of psychology at Claremont Graduate University, in Claremont, Calif. "What we have been noticing in our research is that parental monitoring seems to have a strong relationship to lessening of drug use in young adolescents."

To determine if they were on the right track, Crano and his colleague Andrew Lac, a doctoral student at Claremont, decided to see what other research had found on the effect of parental monitoring on teen drug use --particularly marijuana.

So, Crano and Lac reviewed 17 studies, which involved more than 35,000 people. The studies all had adolescent participants, focused on marijuana and monitoring by parents, and the level of parental monitoring was evaluated by the teens themselves.

"We found the effect was there," Crano said, especially for teenage girls. "It was clear that kids who thought their parents were monitoring them used much less marijuana than kids who didn't."

That finding held true for all 17 studies, Crano said. "The interesting thing is this has to do with kids' perception of parental monitoring, not necessarily what their parents are actually doing," he said.

"If your kids think that you know what they are doing, and where they're at, and who they're with and what they are doing when they are not in your sight, that has a big impact on the kind of trouble they are going to get into," he added.

Crano thinks these findings, published in the November issue of Perspectives on Psychological Science, would hold up if researchers looked at other drug use or other bad behaviors. Continued smoking of marijuana can lead to a number of serious health threats, including depression, cognitive impairment, cardiovascular disease, and certain cancers, the researchers said.

There are two ways parents can monitor their children, Crano said. "Either they watch them like a hawk or the kid discloses what he's up to," he said. Both methods work to keep children away from drugs, he said.

"If parents give the impression to their kids that they really care about them, that they are really watching what they are doing, that they are concerned, that has a strong impact on what the children are going to do in terms of antisocial behavior, which includes marijuana use," Crano said.

R. Gil Kerlikowske, director of the White House Office of National Drug Control Policy, agrees that parents have a key role to play in keeping their children from using drugs.

"It's the most significant role," Kerlikowske said. "A lot of the advertisements, a lot of the information out there has made parents much more comfortable in speaking to their children, particularly about drugs," he said.

The White House drug czar said parental monitoring, along with school and community programs, can be effective ways of steering children away from drugs.

"If you have parents involved in prevention work, and if you have some school-based curriculum around drugs, and there can be some support in neighborhoods and community groups and church -- that is a very strong approach to keeping kids healthy," he said.

More information

For more on what parents can do to keep their kids from drugs, visit the Partnership for a Drug-Free America.

SOURCES: William Crano, Ph.D., professor, psychology, School of Behavioral and Organizational Sciences, Claremont Graduate University, Claremont, Calif.; R. Gil Kerlikowske, director, White House Office of National Drug Control Policy, Washington, D.C.; November 2009 Perspectives on Psychological Science

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