A new study reveals what many parents probably already suspect: A teen's friends play a big role in his or her actions.

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The more sexually active friends a teen has and the more time a teen spends with a boyfriend or girlfriend, the greater the risk that teen will smoke, drink or use drugs, according to the annual report by the National Center on Addiction and Substance Abuse (CASA) at Columbia University.

The study found that compared to teens with no sexually active friends, teens who report half or more of their friends are sexually active are more than 6.5 times likelier to drink; 31 times likelier to get drunk; 22.5 times likelier to have tried marijuana; and more than 5.5 times likelier to smoke.

Teens who spend 25 or more hours a week with a boyfriend or girlfriend are 2.5 times likelier to drink; five times likelier to get drunk; 4.5 times likelier to have tried marijuana; and more than 2.5 times likelier to smoke than teens who spend less than 10 hours a week with a significant other.

Girls with boyfriends two or more years older are more than twice as likely to drink; almost six times likelier to get drunk; six times likelier to have tried marijuana; and 4.5 times likelier to smoke than girls whose boyfriends are less than two years older or who do not have a boyfriend.

"The message for parents from this year's survey is clear: The thunder of teen sexual activity and dating behavior may signal the lightning of substance abuse," said Joseph Califano Jr., CASA's chairman.

In other findings, 44 percent of high school students think that boys at their school often or sometimes "push girls to drink alcohol or take drugs in order to get the girls to have sex or do other sexual things."

Forty-five percent of teens have friends who regularly view and download pornography from the Internet; these teens are at increased risk of smoking, drinking or using illegal drugs, according to the study.

But teens who attend religious services weekly are at less than half the risk of smoking, drinking or using illegal drugs as teens who do not attend such services.

Califino said parents should be alert to their children's friends' activities.

"Parents, make sure you are aware of the dating practices of your child and get to know your child's friends," said Califano.

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