The parents of teenagers’ friends can have as much effect on teens’ decisions about substance use as their own parents, a new study suggests.

If the parents of a teenager’s friends are not aware of their own child’s alcohol or drug use, or condone it, then it is more likely the teen will drink or smoke, the study found.

“Among friendship groups with ‘good parents’ there’s a synergistic effect — if your parents are consistent and aware of your whereabouts, and your friends’ parents are also consistent and aware of their (children’s) whereabouts, then you are less likely to use substances,” study author Michael Cleveland at Penn State University, said in a news release. “But if you belong to a friendship group whose parents are inconsistent, and your parents are consistent, you’re still more likely to use alcohol.”

The study included 9,000 ninth graders, who were asked about their closest friends, their parents’ discipline, and whether their parents knew who their friends were, HealthDay reports. The researchers broke the teens down into about 900 groups of friends. A year later, the teens were surveyed about their substance use.

The researchers found substance use in tenth grade was significantly related to parenting behavior of friends’ parents. This was true even after taking into account the effects of the teenagers’ own parents’ behaviors, and their friends’ substance use.

“I think that it empowers parents to know that not only can they have an influence on their own children, but they can also have a positive influence on their children’s friends as well,” said Cleveland. “And that by acting together — the notion of ‘it takes a village’ — can actually result in better outcomes for adolescents.”

The study appears in the Journal of Studies on Alcohol and Drugs.